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嶋川 銀河大学院農学研究科 生命機能科学専攻助教
研究活動情報
■ 受賞- 2024年05月 マリンバイオテクノロジー学会, 論文賞, Different Responses of Photosynthesis to Nitrogen Starvation Between Highly Oil-Accumulative Diatoms, Fistulifera solaris and Mayamaea sp. JPCC CTDA0820
- 2018年10月 Signalisation rétrograde des organites endosymbiotiques, SEB Travel Grant Award, The mechanism in chloroplasts triggering senescence of barley leaves
- 2015年10月 International Meeting Photosynthesis Research for Sustainability – 2015, Young Talents Award, Flavodiiron 2 and 4 proteins mediate an O2-dependent alternative electron flow in Synechocystis sp. PCC 6803 under CO2-limited conditions
- 2015年03月 神戸大学大学院農学研究科, 六篠賞
- 2014年05月 第5回 日本光合成学会年会, ポスター賞, ランソウFlavodiiron proteinによるAlternative electron flowの機能解明とその活性評価
- 2024年11月, Biochimica et Biophysica Acta (BBA) - Bioenergetics研究論文（学術雑誌）
- 2024年03月, Journal of Biosciences研究論文（学術雑誌）
- Abstract Anion transporters sustain a variety of physiological states in cells. Bestrophins belong to a Cl− and/or HCO3− transporter family conserved in bacteria, animals, algae, and plants. Recently, putative bestrophins were found in the green alga Chlamydomonas reinhardtii, where they are up-regulated under low CO2 conditions and play an essential role in the CO2-concentrating mechanism (CCM). The putative bestrophin orthologs are also conserved in diatoms, secondary endosymbiotic algae harboring red-type plastids, but their physiological functions are unknown. Here, we characterized the subcellular localization and expression profile of bestrophins (BSTs) in the marine diatoms Phaeodactylum tricornutum (PtBST1−4) and Thalassiosira pseudonana (TpBST1 and 2). PtBST1, PtBST2, and PtBST4 localized at the stroma thylakoid membrane outside of the pyrenoid, and PtBST3 localized in the pyrenoid. Contrarily, TpBST1 and TpBST2 both localized in the pyrenoid. These bestrophin proteins accumulated in cells grown in atmospheric CO2 (LC) but not in 1% CO2 (HC)-grown cells. To assess the physiological functions, we generated knock-out mutants for the PtBST1gene by genome editing. The lack of PtBST1 decreased photosynthetic affinity for dissolved inorganic carbon to the level comparable to the HC-grown wild type. Furthermore, non-photochemical quenching in LC-grown cells was 1.5–2.0 times higher in the mutants than in the wild type. These data suggest that HCO3− transport at the stroma thylakoid membranes by PtBST1 is a critical part of the CO2-evolving machinery of the pyrenoid in the fully induced CCM and that PtBST1 may modulate photoprotection under CO2-limited environments in P. tricornutum.Oxford University Press (OUP), 2024年03月, Plant Physiology研究論文（学術雑誌）
- Abstract A circadian clock is an essential system that drives the 24-h expression rhythms for adaptation to day–night cycles. The molecular mechanism of the circadian clock has been extensively studied in cyanobacteria harboring the KaiC-based timing system. Nevertheless, our understanding of the physiological significance of the cyanobacterial circadian clock is still limited. In this study, we cultured wild-type Synechococcus elongatus PCC 7942 and circadian clock mutants in day–night cycles at different light qualities and found that the growth of the circadian clock mutants was specifically impaired during 12-h blue light/12-h dark (BD) cycles for the first time. The arrhythmic mutant kaiCAA was further analyzed by photosynthetic measurements. Compared with the wild type, the mutant exhibited decreases in the chlorophyll content, the ratio of photosystem I to II, net O2 evolution rate and efficiency of photosystem II photochemistry during BD cycles. These results indicate that the circadian clock is necessary for the growth and the maintenance of the optimum function of the photosynthetic apparatus in cyanobacteria under blue photoperiodic conditions.Oxford University Press (OUP), 2024年03月, Plant And Cell Physiology, 65(5) (5), 798 - 808研究論文（学術雑誌）
- 2024年01月, Photosynthesis Research研究論文（学術雑誌）
- Marine diatoms are responsible for up to 20% of the annual global primary production by performing photosynthesis in seawater where CO2 availability is limited while HCO3- is abundant. Our previous studies have demonstrated that solute carrier 4 proteins at the plasma membrane of the diatom Phaeodactylum tricornutum facilitate the use of the abundant seawater HCO3-. There has been an unconcluded debate as to whether such HCO3- use capacity may itself supply enough dissolved inorganic carbon (DIC) to saturate the enzyme Rubisco. Here, we show that the θ-type carbonic anhydrase, Ptθ-CA1, a luminal factor of the pyrenoid-penetrating thylakoid membranes, plays an essential role in saturating photosynthesis of P. tricornutum. We isolated and analyzed genome-edited mutants of P. tricornutum defective in Ptθ-CA1. The mutants showed impaired growth in seawater aerated with a broad range of CO2 levels, from atmospheric to 1%. Independently of growth CO2 conditions, the photosynthetic affinity measured as K0.5 for DIC in mutants reached around 2 mm, which is about 10 times higher than K0.5[DIC] of high-CO2-grown wild-type cells that have repressed CO2-concentrating mechanism levels. The results clearly indicate that diatom photosynthesis is not saturated with either seawater-level DIC or even under a highly elevated CO2 environment unless the CO2-evolving machinery is at the core of the pyrenoid.2023年11月, Plant physiology, 193(4) (4), 2298 - 2305, 英語, 国際誌研究論文（学術雑誌）
- SUMMARY The plastid terminal oxidase PTOX controls the oxidation level of the plastoquinone pool in the thylakoid membrane and acts as a safety valve upon abiotic stress, but detailed characterization of its role in protecting the photosynthetic apparatus is limited. Here we used PTOX mutants in two model plants Arabidopsis thaliana and Marchantia polymorpha. In Arabidopsis, lack of PTOX leads to a severe defect in pigmentation, a so‐called variegated phenotype, when plants are grown at standard light intensities. We created a green Arabidopsis PTOX mutant expressing the bacterial carotenoid desaturase CRTI and a double mutant in Marchantia lacking both PTOX isoforms, the plant‐type and the alga‐type PTOX. In both species, lack of PTOX affected the redox state of the plastoquinone pool. Exposure of plants to high light intensity showed in the absence of PTOX higher susceptibility of photosystem I to light‐induced damage while photosystem II was more stable compared with the wild type demonstrating that PTOX plays both, a pro‐oxidant and an anti‐oxidant role in vivo. Our results shed new light on the function of PTOX in the protection of photosystem I and II.Wiley, 2023年11月, The Plant Journal, 117(3) (3), 669 - 678研究論文（学術雑誌）
- 2023年11月, Physiologia Plantarum研究論文（学術雑誌）
- 2023年09月, Plant Physiology
- 2023年06月, Journal of Experimental Botany研究論文（学術雑誌）
- 2023年04月, Marine Biotechnology研究論文（学術雑誌）
- Proteins immobilized on biosilica which have superior reactivity and specificity and are innocuous to natural environments could be useful biological materials in industrial processes. One recently developed technique, living diatom silica immobilization (LiDSI), has made it possible to immobilize proteins, including multimeric and redox enzymes, via a cellular excretion system onto the silica frustule of the marine diatom Thalassiosira pseudonana. However, the number of application examples so far is limited, and the type of proteins appropriate for the technique is still enigmatic. Here, we applied LiDSI to six industrially relevant polypeptides, including protamine, metallothionein, phosphotriesterase, choline oxidase, laccase, and polyamine synthase. Protamine and metallothionein were successfully immobilized on the frustule as protein fusions with green fluorescent protein (GFP) at the N terminus, indicating that LiDSI can be used for polypeptides which are rich in arginine and cysteine. In contrast, we obtained mutants for the latter four enzymes in forms without green fluorescent protein. Immobilized phosphotriesterase, choline oxidase, and laccase showed enzyme activities even after the purification of frustule in the presence of 1% (wt/vol) octylphenoxy poly(ethyleneoxy)ethanol. An immobilized branched-chain polyamine synthase changed the intracellular polyamine composition and silica nanomorphology. These results illustrate the possibility of LiDSI for industrial applications. IMPORTANCE Proteins immobilized on biosilica which have superior reactivity and specificity and are innocuous to natural environments could be useful biological materials in industrial processes. Living diatom silica immobilization (LiDSI) is a recently developed technique for in vivo protein immobilization on the diatom frustule. We aimed to explore the possibility of using LiDSI for industrial applications by successfully immobilizing six polypeptides: (i) protamine (Oncorhynchus keta), a stable antibacterial agent; (ii) metallothionein (Saccharomyces cerevisiae), a metal adsorption molecule useful for bioremediation; (iii) phosphotriesterase (Sulfolobus solfataricus), a scavenger for toxic organic phosphates; (iv) choline oxidase (Arthrobacter globiformis), an enhancer for photosynthetic activity and yield of plants; (v) laccase (Bacillus subtilis), a phenol oxidase utilized for delignification of lignocellulosic materials; and (vi) branched-chain polyamine synthase (Thermococcus kodakarensis), which produces branched-chain polyamines important for DNA and RNA stabilization at high temperatures. This study provides new insights into the field of applied biological materials.2022年10月, Applied and Environmental Microbiology, e0115322, 英語, 国際誌研究論文（学術雑誌）
- Senescence in plants enables resource recycling from senescent leaves to sink organs. Under stress, increased production of reactive oxygen species (ROS) and associated signalling activates senescence. However, senescence is not always associated with stress since it has a prominent role in plant development, in which the role of ROS signalling is less clear. To address this, we investigated lipid metabolism and patterns of lipid peroxidation related to signalling during sequential senescence in first-emerging barley leaves grown under natural light conditions. Leaf fatty acid compositions were dominated by linolenic acid (75 % of total), the major poly-unsaturated fatty acid (PUFA) in galactolipids of thylakoid membranes, known to be highly sensitive to peroxidation. Lipid catabolism during senescence, including increased lipoxygenase activity, led to decreased levels of PUFA and increased levels of short-chain saturated fatty acids. When normalized to leaf area, only concentrations of hexanal, a product from the 13-lipoxygenase pathway, increased early upon senescence, whereas reactive electrophile species (RES) from ROS-associated lipid peroxidation, such as 4-hydroxynonenal, 4-hydroxyhexenal and acrolein, as well as β-cyclocitral derived from oxidation of β-carotene, decreased. However, relative to total chlorophyll, amounts of most RES increased at late-senescence stages, alongside increased levels of α-tocopherol, zeaxanthin and non-photochemical quenching, an energy dissipative pathway that prevents ROS production. Overall, our results indicate that lipid peroxidation derived from enzymatic oxidation occurs early during senescence in first barley leaves, while ROS-derived lipid peroxidation associates weaker with senescence. This article is protected by copyright. All rights reserved.2022年09月, Physiologia Plantarum, e13769, 英語, 国際誌研究論文（学術雑誌）
- Live cyanobacteria and algae integrated onto an extracellular electrode can generate a light-induced current (i.e., a photocurrent). Although the photocurrent is expected to be correlated with the redox environment of the photosynthetic cells, the relationship between the photocurrent and the cellular redox state is poorly understood. Here, we investigated the effect of the reduced nicotinamide adenine dinucleotide phosphate [NADP(H)] redox level of cyanobacterial cells (before light exposure) on the photocurrent using several mutants (Δzwf, Δgnd, and ΔglgP) deficient in the oxidative pentose phosphate (OPP) pathway, which is the metabolic pathway that produces NADPH in darkness. The NAD(P)H redox level and photocurrent in the cyanobacterium Synechocystis sp. PCC 6803 were measured noninvasively. Dysfunction of the OPP pathway led to oxidation of the photosynthetic NADPH pool in darkness. In addition, photocurrent induction was retarded and the current density was lower in Δzwf, Δgnd, and ΔglgP than in wild-type cells. Exogenously added glucose compensated the phenotype of ΔglgP and drove the OPP pathway in the mutant, resulting in an increase in the photocurrent. The results indicated that NADPH accumulated by the OPP pathway before illumination is a key factor for the generation of a photocurrent. In addition, measuring the photocurrent can be a non-invasive approach to estimate the cellular redox level related to NADP(H) pool in cyanobacteria.2022年08月, Photosynthesis Research, 153(1-2) (1-2), 113 - 120, 英語, 国際誌研究論文（学術雑誌）
- Cyclic electron transport (CET) is an attractive hypothesis for regulating photosynthetic electron transport and producing the additional ATP in oxygenic phototrophs. The concept of CET has been established in the last decades, and it is proposed to function in the progenitor of oxygenic photosynthesis, cyanobacteria. The in vivo activity of CET is frequently evaluated either from the redox state of the reaction center chlorophyll in photosystem (PS) I, P700, in the absence of PSII activity or by comparing PSI and PSII activities through the P700 redox state and chlorophyll fluorescence, respectively. The evaluation of CET activity, however, is complicated especially in cyanobacteria, where CET shares the intersystem chain, including plastoquinone, cytochrome b6/f complex, plastocyanin, and cytochrome c6, with photosynthetic linear electron transport (LET) and respiratory electron transport (RET). Here we sought to distinguish the in vivo electron transport rates in RET and CET in the cyanobacterium Synechocystis sp. PCC 6803. The reduction rate of oxidized P700 (P700+) decreased to less than 10% when PSII was inhibited, indicating that PSII is the dominant electron source to PSI but P700+ is also reduced by electrons derived from other sources. The oxidative pentose phosphate (OPP) pathway functions as the dominant electron source for RET, which was found to be inhibited by glycolaldehyde (GA). In the condition where the OPP pathway and respiratory terminal oxidases were inhibited by GA and KCN, the P700+ reduction rate was less than 1% of that without any inhibitors. This study indicate that the electron transport to PSI when PSII is inhibited is dominantly derived from the OPP pathway in Synechocystis sp. PCC 6803.2022年07月, Journal of Plant Research, 135(4) (4), 555 - 564, 英語, 国内誌研究論文（学術雑誌）
- Biophotovoltaics (BPV) generates electricity from reducing equivalent(s) produced by photosynthetic organisms by exploiting a phenomenon called extracellular electron transfer (EET), where reducing equivalent(s) is transferred to external electron acceptors. Although cyanobacteria have been extensively studied for BPV because of their high photosynthetic activity and ease of handling, their low EET activity poses a limitation. Here, we show an order-of-magnitude enhancement in photocurrent generation of the cyanobacterium Synechocystis sp. PCC 6803 by deprivation of the outer membrane, where electrons are suggested to stem from pathway(s) downstream of photosystem I. A marked enhancement of EET activity itself is verified by rapid reduction of exogenous electron acceptor, ferricyanide. The extracellular organic substances, including reducing equivalent(s), produced by this cyanobacterium serve as respiratory substrates for other heterotrophic bacteria. These findings demonstrate that the outer membrane is a barrier that limits EET. Therefore, depriving this membrane is an effective approach to exploit the cyanobacterial reducing equivalent(s).2022年06月, Nature communications, 13(1) (1), 3067 - 3067, 英語, 国際誌研究論文（学術雑誌）
- Light capture by chlorophylls and photosynthetic electron transport bury the risk of the generation of reactive oxygen species (ROS) including singlet oxygen, superoxide anion radicals and hydrogen peroxide. Rapid changes in light intensity, electron fluxes and accumulation of strong oxidants and reductants increase ROS production. Superoxide is mainly generated at the level of photosystem I while photosystem II is the main source of singlet oxygen. ROS can induce oxidative damage of the photosynthetic apparatus, however, ROS are also important to tune processes inside the chloroplast and participate in retrograde signalling regulating the expression of genes involved in acclimation responses. Under most physiological conditions light harvesting and photosynthetic electron transport are regulated to keep the level of ROS at a non-destructive level. Photosystem II is most prone to photoinhibition but can be quickly repaired while photosystem I is protected in most cases. The size of the transmembrane proton gradient is central for the onset of mechanisms that protect against photoinhibition. The proton gradient allows dissipation of excess energy as heat in the antenna systems and it regulates electron transport. pH-dependent slowing down of electron donation to photosystem I protects it against ROS generation and damage. Cyclic electron transfer and photoreduction of oxygen contribute to the size of the proton gradient. The yield of singlet oxygen production in photosystem II is regulated by changes in the midpoint potential of its primary quinone acceptor. In addition, numerous antioxidants inside the photosystems, the antenna and the thylakoid membrane quench or scavenge ROS.2022年04月, Biochemical Society transactions, 50(2) (2), 1025 - 1034, 英語, 国際誌研究論文（学術雑誌）
- Photosynthesis in cyanobacteria, green algae, and basal land plants is protected against excess reducing pressure on the photosynthetic chain by flavodiiron proteins (FLV) that dissipate photosynthetic electrons by reducing O2. In these organisms, the genes encoding FLV are always conserved in the form of a pair of two-type isozymes (FLVA and FLVB) that are believed to function in O2 photo-reduction as a heterodimer. While coral symbionts (dinoflagellates of the family Symbiodiniaceae) are the only algae to harbor FLV in photosynthetic red plastid lineage, only one gene is found in transcriptomes and its role and activity remain unknown. Here, we characterized the FLV genes in Symbiodiniaceae and found that its coding region is composed of tandemly repeated FLV sequences. By measuring the O2-dependent electron flow and P700 oxidation, we suggest that this atypical FLV is active in vivo. Based on the amino-acid sequence alignment and the phylogenetic analysis, we conclude that in coral symbionts, the gene pair for FLVA and FLVB have been fused to construct one coding region for a hybrid enzyme, which presumably occurred when or after both genes were inherited from basal green algae to the dinoflagellate. Immunodetection suggested the FLV polypeptide to be cleaved by a post-translational mechanism, adding it to the rare cases of polycistronic genes in eukaryotes. Our results demonstrate that FLV are active in coral symbionts with genomic arrangement that is unique to these species. The implication of these unique features on their symbiotic living environment is discussed.Springer Science and Business Media {LLC}, 2022年01月, Photosynthesis Research, 151(1) (1), 113 - 124, 英語, 国際誌研究論文（学術雑誌）
- Photosynthesis has to work efficiently in contrasting environments such as in shade and full sun. Rapid changes in light intensity and over-reduction of the photosynthetic electron transport chain cause production of reactive oxygen species, which can potentially damage the photosynthetic apparatus. Thus, to avoid such damage, photosynthetic electron transport is regulated on many levels, including light absorption in antenna, electron transfer reactions in the reaction centers, and consumption of ATP and NADPH in different metabolic pathways. Many regulatory mechanisms involve the movement of protein-pigment complexes within the thylakoid membrane. Furthermore, a certain number of chloroplast proteins exist in different oligomerization states, which temporally associate to the thylakoid membrane and modulate their activity. This review starts by giving a short overview of the lipid composition of the chloroplast membranes, followed by describing supercomplex formation in cyclic electron flow. Protein movements involved in the various mechanisms of non-photochemical quenching, including thermal dissipation, state transitions and the photosystem II damage-repair cycle are detailed. We highlight the importance of changes in the oligomerization state of VIPP and of the plastid terminal oxidase PTOX and discuss the factors that may be responsible for these changes. Photosynthesis-related protein movements and organization states of certain proteins all play a role in acclimation of the photosynthetic organism to the environment.2021年05月, Cells, 10(5) (5), 英語, 国際誌研究論文（学術雑誌）
- Photosynthetic organisms commonly develop the strategy to keep the reaction center chlorophyll of photosystem I, P700, oxidized for preventing the generation of reactive oxygen species in excess light conditions. In photosynthesis of C4 plants, CO2 concentration is kept at higher levels around ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) by the cooperation of the mesophyll and bundle sheath cells, which enables them to assimilate CO2 at higher rates to survive under drought stress. However, the regulatory mechanism of photosynthetic electron transport for P700 oxidation is still poorly understood in C4 plants. Here, we assessed gas exchange, chlorophyll fluorescence, electrochromic shift, and near infrared absorbance in intact leaves of maize (a NADP-malic enzyme C4 subtype species) in comparison with mustard, a C3 plant. Instead of the alternative electron sink due to photorespiration in the C3 plant, photosynthetic linear electron flow was strongly suppressed between photosystems I and II, dependent on the difference of proton concentration across the thylakoid membrane (ΔpH) in response to the suppression of CO2 assimilation in maize. Linear relationships among CO2 assimilation rate, linear electron flow, P700 oxidation, ΔpH, and the oxidation rate of ferredoxin suggested that the increase of ΔpH for P700 oxidation was caused by the regulation of proton conductance of chloroplast ATP synthase but not by promoting cyclic electron flow. At the scale of intact leaves, the ratio of PSI to PSII was estimated almost 1:1 in both C3 and C4 plants. Overall, the photosynthetic electron transport was regulated for P700 oxidation in maize through the same strategies as in C3 plants only except for the capacity of photorespiration despite the structural and metabolic differences in photosynthesis between C3 and C4 plants.2021年05月, International Journal of Molecular Sciences, 22(9) (9), 英語, 国際誌研究論文（学術雑誌）
- In photosynthetic organisms, it is recognized that the intracellular redox ratio of NADPH is regulated within an appropriate range for the cooperative function of a wide variety of physiological processes. However, despite its importance, there is large variability in the values of the NADPH fraction [NADPH/(NADPH + NADP+)] quantitatively estimated to date. In the present study, the light response of the NADPH fraction was investigated by applying a novel NADP(H) extraction method using phenol / chloroform / isoamyl alcohol (PCI) in the cyanobacterium Synechocystis sp. PCC 6803. The light response of NADP(H) observed using PCI extraction was qualitatively consistent with the NAD(P)H fluorescence time course measured in vivo. Moreover, the results obtained by PCI extraction and the fluorescence-based methods were also consistent in a mutant lacking the ability to oxidize NAD(P)H in the respiratory chain, and exhibiting a unique NADPH light response. These observations indicate that the PCI extraction method allowed quantitative determination of NADP(H) redox. Notably, the PCI extraction method showed that not all NADP(H) was oxidized or reduced by light-dark transition. Specifically, the fraction of NADPH was 42% in the dark-adapted cell, and saturated at 68% in light conditions.2021年05月, Photosynthesis research, 148(1-2) (1-2), 57 - 66, 英語, 国際誌研究論文（学術雑誌）
- The liverwort Marchantia polymorpha contains two isoforms of the plastid terminal oxidase (PTOX), an enzyme that catalyzes the reduction of oxygen to water using plastoquinol as substrate. Phylogenetic analyses showed that one isoform, here called MpPTOXa, is closely related to isoforms occurring in plants and some algae, while the other isoform, here called MpPTOXb, is closely related to the two isoforms occurring in Chlamydomonas reinhardtii. Mutants of each isoform were created in Marchantia polymorpha using CRISPR/Cas9 technology. While no obvious phenotype was found for these mutants, chlorophyll fluorescence analyses demonstrated that the plastoquinone pool was in a higher reduction state in both mutants. This was visible at the level of fluorescence measured in dark-adapted material and by post illumination fluorescence rise. These results suggest that both isoforms have a redundant function. However, when P700 oxidation and re-reduction was studied, differences between these two isoforms were observed. Furthermore, the mutant affected in MpPTOXb showed a slight alteration in the pigment composition, a higher non-photochemical quenching and a slightly lower electron transport rate through photosystem II. These differences may be explained either by differences in the enzymatic activities or by different activities attributed to preferential involvement of the two PTOX isoforms to either linear or cyclic electron flow.2021年01月, Biochimica et biophysica acta. Bioenergetics, 1862(1) (1), 148309 - 148309, 英語, 国際誌研究論文（学術雑誌）
- Microbial extracellular electron transfer (EET) to solid-state electron acceptors such as anodes and metal oxides, which was originally identified in dissimilatory metal-reducing bacteria, is a key process in microbial electricity generation and the biogeochemical cycling of metals. Although it is now known that photosynthetic microorganisms can also generate (photo)currents via EET, which has attracted much interest in the field of biophotovoltaics, little is known about the reduction of metal (hydr)oxides via photosynthetic microbial EET. The present work quantitatively assessed the reduction of ferrihydrite in conjunction with the EET of the photosynthetic microbe Synechocystis sp. PCC 6803. Microbial reduction of ferrihydrite was found to be initiated in response to light but proceeded at higher rates when exogenous glucose was added, even under dark conditions. These results indicate that current generation from Synechocystis cells does not always need light irradiation. The qualitative trends exhibited by the ferrihydrite reduction rates under various conditions showed significant correlation with those of the microbial currents. Notably, the maximum concentration of Fe(II) generated by the cyanobacterial cells under dark conditions in the presence of glucose was comparable to the levels observed in the photic layers of Fe-rich microbial mats.2021年, Frontiers in microbiology, 12, 650832 - 650832, 英語, 国際誌研究論文（学術雑誌）
- Against the potential risk in oxygenic photosynthesis, that is, the generation of reactive oxygen species, photosynthetic electron transport needs to be regulated in response to environmental fluctuations. One of the most important regulations is keeping the reaction center chlorophyll (P700) of photosystem I in its oxidized form in excess light conditions. The oxidation of P700 is supported by dissipating excess electrons safely to O2, and we previously found that the molecular mechanism of the alternative electron sink is changed from flavodiiron proteins (FLV) to photorespiration in the evolutionary history from cyanobacteria to plants. However, the overall picture of the regulation of photosynthetic electron transport is still not clear in bryophytes, the evolutionary intermediates. Here, we investigated the physiological roles of FLV and photorespiration for P700 oxidation in the liverwort Marchantia polymorpha by using the mutants deficient in FLV (flv1) at different O2 partial pressures. The effective quantum yield of photosystem II significantly decreased at 2kPa O2 in flv1, indicating that photorespiration functions as the electron sink. Nevertheless, it was clear from the phenotype of flv1 that FLV was dominant for P700 oxidation in M. polymorpha. These data suggested that photorespiration has yet not replaced FLV in functioning for P700 oxidation in the basal land plant probably because of the lower contribution to lumen acidification, compared with FLV, as reflected in the results of electrochromic shift analysis.2021年, Frontiers in plant science, 12, 668805 - 668805, 英語, 国際誌研究論文（学術雑誌）
- In eukaryotic algae, respiratory O2 uptake is enhanced after illumination, which is called light-enhanced respiration (LER). It is likely stimulated by an increase in respiratory substrates produced during photosynthetic CO2 assimilation and function in keeping the metabolic and redox homeostasis in the light in eukaryotic cells, based on the interactions among the cytosol, chloroplasts, and mitochondria. Here, we first characterize LER in photosynthetic prokaryote cyanobacteria, in which respiration and photosynthesis share their metabolisms and electron transport chains in one cell. From the physiological analysis, the cyanobacterium Synechocystis sp. PCC 6803 performs LER, similar to eukaryotic algae, which shows a capacity comparable to the net photosynthetic O2 evolution rate. Although the respiratory and photosynthetic electron transports share the interchain, LER was uncoupled from photosynthetic electron transport. Mutant analyses demonstrated that LER is motivated by the substrates directly provided by photosynthetic CO2 assimilation, but not by glycogen. Further, the light-dependent activation of LER was observed even with exogenously added glucose, implying a regulatory mechanism for LER in addition to the substrate amounts. Finally, we discuss the physiological significance of the large capacity of LER in cyanobacteria and eukaryotic algae compared to those in plants that normally show less LER.2020年12月, International Journal of Molecular Sciences, 22(1) (1), 英語, 国際誌研究論文（学術雑誌）
- Leaf senescence is an important process for plants to remobilize a variety of metabolites and nutrients to sink tissues, such as developing leaves, fruits and seeds. It has been suggested that reactive oxygen species (ROS) play an important role in the initiation of leaf senescence. Flag leaves of two different barley varieties, cv. Lomerit and cv. Carina, showed differences in the loss of photosystems and in the production of ROS at a late stage of senescence after significant loss of chlorophyll (Krieger-Liszkay et al. 2015). Here, we investigated photosynthetic electron transport and ROS production in primary leaves of these two varieties at earlier stages of senescence. Comparisons were made between plants grown outside in natural light and temperatures and plants grown in temperature-controlled growth chambers under low light intensity. Alterations in the content of photoactive P700, ferredoxin and plastocyanin (PC) photosynthetic electron transport were analyzed using in vivo near-infrared absorbance changes and chlorophyll fluorescence, while ROS were measured with spin-trapping electron paramagnetic resonance spectroscopy. Differences in ROS production between the two varieties were only observed in outdoor plants, whereas a loss of PC was common in both barley varieties regardless of growth conditions. We conclude that the loss of PC is the earliest detectable photosynthetic parameter of leaf senescence while differences in the production of individual ROS species occur later and depend on environmental factors.2020年12月, Plant & cell physiology, 61(11) (11), 1986 - 1994, 英語, 国内誌研究論文（学術雑誌）
- Upon exposure to environmental stress, the primary electron donor in photosystem I (PSI), P700, is oxidized to suppress the production of reactive oxygen species that could oxidatively inactivate the function of PSI. The illumination of rice leaves with actinic light induces intrinsic fluctuations in the opening and closing of stomata, causing the net CO2 assimilation rate to fluctuate. We examined the effects of these intrinsic fluctuations on electron transport reactions. Under atmospheric O2 conditions (21 kPa), the effective quantum yield of photosystem II (PSII) (Y(II)) remained relatively high while the net CO2 assimilation rate fluctuated, which indicates the function of alternative electron flow. By contrast, under low O2 conditions (2 kPa), Y(II) fluctuated. These results suggest that photorespiration primarily drove the alternative electron flow. Photorespiration maintained the oxidation level of ferredoxin (Fd) throughout the fluctuation of the net CO2 assimilation rate. Moreover, the relative activity of photorespiration was correlated with both the oxidation level of P700 and the magnitude of the proton gradient across the thylakoid membrane in 21 kPa O2 conditions. These results show that photorespiration oxidized P700 by stimulating the proton gradient formation when CO2 assimilation was suppressed by stomatal closure.{MDPI} {AG}, 2020年12月, Plants, 9(12) (12), 1761 - 1761, 英語, 国際誌研究論文（学術雑誌）
- As an adaptation to periodic fluctuations of environmental light, photosynthetic organisms have evolved a circadian clock. Control by the circadian clock of many cellular physiological functions, including antioxidant enzymes, metabolism and the cell cycle, has attracted attention in the context of oxidative stress tolerance. However, since each physiological function works in an integrated manner to deal with oxidative stress, whether or not cell responses to oxidative stress are under circadian control remains an open question. In fact, circadian rhythms of oxidative stress tolerance have not yet been experimentally demonstrated. In the present work, we applied an assay using methyl viologen (MV), which generates reactive oxygen species (ROS) under light irradiation, and experimentally verified the circadian rhythms of oxidative stress tolerance in photosynthetic cells of the cyanobacterium Synechococcus elongatus PCC 7942, a standard model species for investigation of the circadian clock. Here, we report that ROS generated by MV treatment causes damage to stroma components and not to the photosynthetic electron transportation chain, leading to reduced cell viability. The degree of decrease in cell viability was dependent on the subjective time at which oxidative stress was applied. Thus, oxidative stress tolerance was shown to exhibit circadian rhythms. In addition, the rhythmic pattern of oxidative stress tolerance disappeared in mutant cells lacking the essential clock genes. Notably, ROS levels changed periodically, independent of the MV treatment. Thus, we demonstrate for the first time that in cyanobacterial cells, oxidative stress tolerance shows circadian oscillation.2020年11月, Scientific reports, 10(1) (1), 20029 - 20029, 英語, 国際誌研究論文（学術雑誌）
- Flavodiiron proteins (FDPs) of photosynthetic organisms play a photoprotective role by reducing oxygen to water and thus avoiding the accumulation of excess electrons on the photosystem I (PSI) acceptor side under stress conditions. In Synechocystis sp. PCC 6803 grown under high CO2, both FDPs Flv1 and Flv3 are indispensable for oxygen reduction. We performed a detailed in vivo kinetic study of wild-type (WT) and Δflv1/3 strains of Synechocystis using light-induced NADPH fluorescence and near-infrared absorption of iron-sulfur clusters from ferredoxin and the PSI acceptors (FAFB), collectively named FeS. These measurements were performed under conditions where the Calvin-Benson cycle is inactive or poorly activated. Under such conditions, the NADPH decay following a short illumination decays in parallel in both strains and exhibits a time lag which is correlated to the presence of reduced FeS. On the contrary, reduced FeS decays much faster in WT than in Δflv1/3 (13 vs 2 s-1). These data unambiguously show that reduced ferredoxin, or possibly reduced FAFB, is the direct electron donor to the Flv1/Flv3 heterodimer. Evidences for large reduction of (FAFB) and recombination reactions within PSI were also provided by near-infrared absorption. Mutants lacking either the NDH1-L complex, the homolog of complex I of respiration, or the Pgr5 protein show no difference with WT in the oxidation of reduced FeS following a short illumination. These observations question the participation of a significant cyclic electron flow in cyanobacteria during the first seconds of the induction phase of photosynthesis.2020年10月, Biochimica et biophysica acta. Bioenergetics, 1861(10) (10), 148256 - 148256, 英語, 国際誌研究論文（学術雑誌）
- Pgr5 proteins play a major direct role in cyclic electron flow paths in plants and eukaryotic phytoplankton. The genomes of many cyanobacterial species code for Pgr5-like proteins but their function is still uncertain. Here, we present evidence that supports a link between the Synechocystis sp. PCC6803 Pgr5-like protein and the regulation of intracellular redox balance. The knockout strain, pgr5KO, did not display substantial phenotypic response under our experimental conditions, confirming results obtained in earlier studies. However, the overexpression strain, pgr5OE, accumulated 2.5-fold more chlorophyll than the wild type and displayed increased content of photosystems matching the chlorophyll increase. As a result, electron transfer rates through the photosynthetic apparatus of pgr5OE increased, as did the amount of energy stored as glycogen. While, under photoautotrophic conditions, this metabolic difference had only minor effects, under mixotrophic conditions, pgr5OE cultures collapsed. Interestingly, this specific phenotype of pgr5OE mutants displayed a tendency for reverting, and cultures which previously collapsed in the presence of glucose were now able to survive. DNA sequencing of a pgr5OE strain revealed a second site suppression mutation in slr1916, a putative esterase associated with redox regulation. The phenotype of the slr1916 knockout is very similar to that of the strain reported here and to that of the pmgA regulator knockout. These data demonstrate that, in Synechocystis 6803, there is strong selection against overexpression of the Pgr5-like protein. The pseudoreversion event in a gene involved in redox regulation suggests a connection of the Pgr5-like protein to this network.{MDPI} {AG}, 2020年09月, Life, 10(9) (9), 174 - 174, 英語, 国際誌研究論文（学術雑誌）
- Oxygenic photosynthesis converts light energy into chemical energy via electron transport and assimilates CO2 in the Calvin-Benson cycle with the chemical energy. Thus, high light and low CO2 conditions induce the accumulation of electrons in the photosynthetic electron transport system, resulting in the formation of reactive oxygen species. To prevent the accumulation of electrons, oxygenic photosynthetic organisms have developed photoprotection mechanisms, including non-photochemical quenching (NPQ) and alternative electron flow (AEF). There are diverse molecular mechanisms underlying NPQ and AEF, and the corresponding molecular actors have been identified and characterized using a model green alga Chlamydomonas reinhardtii. In contrast, detailed information about the photoprotection mechanisms is lacking for other green algal species. In the current study, we examined the photoprotection mechanisms responsive to CO2 in the green alga Chlorella variabilis by combining the analyses of pulse-amplitude-modulated fluorescence, O2 evolution, and the steady-state and time-resolved fluorescence spectra. Under the CO2-limited condition, ΔpH-dependent NPQ occurred in photosystems I and II. Moreover, O2-dependent AEF was also induced. Under the CO2-limited condition with carbon supplementation, NPQ was relaxed and light-harvesting chlorophyll-protein complex II was isolated from both photosystems. In C. variabilis, the O2-dependent AEF and the mechanisms that instantly convert the light-harvesting functions of both photosystems may be important for maintaining efficient photosynthetic activities under various CO2 conditions.2020年06月, Photosynthesis research, 144(3) (3), 397 - 407, 英語, 国際誌研究論文（学術雑誌）
- In photosynthesis research, non-invasive in vivo spectroscopic analyses have been used as a practical tool for studying photosynthetic electron transport. Klas-NIR spectrophotometer has been recently developed by Klughammer and Schreiber (Photosynth Res 128:195-214, 2016) for in vivo measurements of redox changes of P700, plastocyanin (Pcy) and ferredoxin (Fd). Here we show examples using the Klas-NIR spectrophotometer for the evaluation of the redox states and quantities of these components in plant leaves and cyanobacterial suspensions. The redox poise under light of the electron transport components is different in leaves from higher plants compared with cyanobacteria. During a short illumination with an actinic light, P700, Pcy, and Fd are kept reduced in barley leaves but are oxidized in cyanobacteria. During far-red light illumination, P700 and Pcy are mostly oxidized in the leaves but are partially kept reduced in cyanobacteria. In the cyanobacterium, Thermosynechococcus elongatus, which has no Pcy but uses cytochrome c6 (cyt c6) as the electron donor to photosystem I, a cyt c6 signal was detected in vivo. To show the potential of Klas-NIR spectrophotometer for studying different developmental stages of a leaf, we performed measurements on fully mature and early senescing barley leaves. Pcy content in leaves decreased during senescence at an early stage. The Pcy loss was quantitatively analyzed using Klas-NIR spectrophotometer, giving absolute ratios of Pcy to PSI of 2.5 and 1.6 in younger and older leaves, respectively. For quantification of the signals in vivo, in vitro data (Sétif et al. in Photosynth Res142:307-319, 2019) obtained with Klas-NIR spectrophotometer were used.Springer Science and Business Media {LLC}, 2020年04月, Photosynthesis Research, 144(1) (1), 63 - 72, 英語, 国際誌研究論文（学術雑誌）
- Elsevier, 2020年, Advances in Botanical Research, 151 - 176[査読有り]論文集(書籍)内論文
- Leaves of Arabidopsis thaliana plants grown in short days (8 h light) generate more reactive oxygen species in the light than leaves of plants grown in long days (16 h light). The importance of the two PsaE isoforms of photosystem I, PsaE1 and PsaE2, for O2 reduction was studied in plants grown under these different growth regimes. In short day conditions a mutant affected in the amount of PsaE1 (psae1-1) reduced more efficiently O2 than a mutant lacking PsaE2 (psae2-1) as shown by spin trapping EPR spectroscopy on leaves and by following the kinetics of P700+ reduction in isolated photosystem I. In short day conditions higher O2 reduction protected photosystem II against photoinhibition in psae1-1. In contrast in long day conditions the presence of PsaE1 was clearly beneficial for photosynthetic electron transport and for the stability of the photosynthetic apparatus under photoinhibitory conditions. We conclude that the two PsaE isoforms have distinct functions and we propose that O2 reduction at photosystem I is beneficial for the plant under certain environmental conditions.2020年01月, Biochimica et biophysica acta. Bioenergetics, 1861(1) (1), 148089 - 148089, 英語, 国際誌研究論文（学術雑誌）
- Senescence is the last stage of leaf development preceding the death of the organ, and it is important for nutrient remobilization and for feeding sink tissues. There are many reports on leaf senescence, but the mechanisms initiating leaf senescence are still poorly understood. Leaf senescence is affected by many environmental factors and seems to vary in different species and even varieties of plants, which makes it difficult to generalize the mechanism. Here, we give an overview on studies reporting about alterations in the composition of the photosynthetic electron transport chain in chloroplasts during senescence. We hypothesize that alternative electron flow and related generation of the proton motive force required for ATP synthesis become increasingly important during progression of senescence. We address the generation of reactive oxygen species (ROS) in chloroplasts in the initiation of senescence, retrograde signaling from the chloroplast to the nucleus and ROS-dependent signaling associated with leaf senescence. Finally, a few ideas for increasing crop yields by increasing the chloroplast lifespan are presented.2019年05月, Physiologia plantarum, 166(1) (1), 148 - 164, 英語, 国際誌研究論文（学術雑誌）
- PSI has the potential to generate reactive oxygen species and be oxidatively inactivated by the reactive oxygen species. The photo-oxidative damage of PSI (also called PSI photoinhibition) causes the inhibition of the plant growth and is a lethal event for plants. It has been reported that PSI photoinhibition does not occur as long as the reaction-center chlorophyll (P700) remains oxidized, even in excess light conditions. This process is termed P700 oxidation and is supported by various regulatory mechanisms and likely also by the stoichiometric quantities of photosynthetic apparatus. In this study, we assessed how decreased photochemically active PSI in Arabidopsis (Arabidopsis thaliana) affected a variety of photosynthetic parameters, including P700 oxidation. Inactivation of PSI was rapidly and selectively induced by repetitive short-pulse illumination. PSI photoinhibition correlated linearly with decreases in effective quantum yield of PSII and nonphotochemical quenching; however, the photosynthetic CO2 assimilation rate was less affected, as exemplified by ∼50% of the normal CO2 assimilation rate maintained with an 80% loss in PSI photochemical activity. In contrast, effective quantum yield of PSI was enhanced following PSI photoinhibition, mainly owing to a decrease in the electron donor-side limitation of PSI. Based on these results, we propose that the stoichiometric quantity of PSI is optimized to induce P700 oxidation for dissipating excess light energy in PSI, thus avoiding inhibition of photosynthetic CO2 assimilation caused by PSI photoinhibition.American Society of Plant Biologists ({ASPB}), 2019年04月, Plant Physiology, 179(4) (4), 1479 - 1485, 英語, 国際誌研究論文（学術雑誌）
- While subject to illumination, photosystem I (PSI) has the potential to produce reactive oxygen species (ROS) that can cause photo-oxidative damage in oxygenic photoautotrophs. The reaction center chlorophyll in PSI (P700) is kept oxidized in excess light conditions to limit over-excitation of PSI and alleviate the production of ROS. Oxidation of P700 requires a sufficient electron sink for PSI, which is responsible for flavodiiron proteins (FLV) safely dissipating electrons to O2 in cyanobacteria, green algae, and land plants except for angiosperms during short-pulse light (SP) illumination under which photosynthesis and photorespiration do not occur. This fact implies that O2 usage is essential for P700 oxidation but also raises the question why angiosperms lost FLV. Here, we first found that aquatic photoautotrophs in red plastid lineage, in which no gene for FLV has been found, could keep P700 oxidized during SP illumination alleviating the photo-oxidative damage in PSI even without O2 usage. We comprehensively assessed P700 oxidation during SP illumination in the presence and absence of O2 in cyanobacteria (Cyanophyta), green algae (Chlorophyta), angiosperms (Streptophyta), red algae (Rhodophyta), and secondary algae (Cryptophyta, Haptophyta, and Heterokontophyta). A variety of dependencies of P700 oxidation on O2 among these photoautotrophs clearly suggest that O2 usage and FLV are not universally required to oxidize P700 for protecting PSI against ROS damage. Our results expand the understanding of the diverse strategies taken by oxygenic photoautotrophs to oxidize P700 and mitigate the risks of ROS.Springer Science and Business Media {LLC}, 2019年03月, Photosynthesis Research, 139(1-3) (1-3), 401 - 411, 英語, 国際誌研究論文（学術雑誌）
- Sugar metabolism pathways such as photosynthesis produce dicarbonyls, e.g. methylglyoxal (MG), which can cause cellular damage. The glyoxalase (GLX) system comprises two enzymes GLX1 and GLX2, and detoxifies MG; however, this system is poorly understood in the chloroplast, compared with the cytosol. In the present study, we determined GLX1 and GLX2 activities in spinach chloroplasts, which constituted 40% and 10%, respectively, of the total leaf glyoxalase activity. In Arabidopsis thaliana, five GFP-fusion GLXs were present in the chloroplasts. Under high CO2 concentrations, where increased photosynthesis promotes the MG production, GLX1 and GLX2 activities in A. thaliana increased and the expression of AtGLX1-2 and AtGLX2-5 was enhanced. On the basis of these findings and the phylogeny of GLX in oxygenic phototrophs, we propose that the GLX system scavenges MG produced in chloroplasts during photosynthesis.2018年12月, Bioscience, biotechnology, and biochemistry, 82(12) (12), 2072 - 2083, 英語, 国際誌研究論文（学術雑誌）
- Oxygenic phototrophs are vulnerable to damage by reactive oxygen species (ROS) that are produced in photosystem I (PSI) by excess photon energy over the demand of photosynthetic CO2 assimilation. In plant leaves, repetitive short-pulse (rSP) illumination produces ROS to inactivate PSI. The production of ROS is alleviated by oxidation of the reaction center chlorophyll in PSI, P700, during the illumination with the short-pulse light, which is supported by flavodiiron protein (FLV). In this study, we found that in the cyanobacterium Synechocystis sp. PCC 6803 P700 was oxidized and PSI was not inactivated during rSP illumination even in the absence of FLV. Conversely, the mutant deficient in respiratory terminal oxidases was impaired in P700 oxidation during the illumination with the short-pulse light to suffer from photo-oxidative damage in PSI. Interestingly, the other cyanobacterium Synechococcus sp. PCC 7002 could not oxidize P700 without FLV during rSP illumination. These data indicate that respiratory terminal oxidases are critical to protect PSI from ROS damage during rSP illumination in Synechocystis sp. PCC 6803 but not Synechococcus sp. PCC 7002.Springer Science and Business Media {LLC}, 2018年08月, Photosynthesis Research, 137(2) (2), 241 - 250, 英語, 国際誌研究論文（学術雑誌）
- Natural sunlight exceeds the demand of photosynthesis such that it can cause plants to produce reactive oxygen species (ROS), which subsequently cause photo-oxidative damage. Because photosystem I (PSI) is a major source of ROS, plants actively maintain the reaction center chlorophyll of PSI(P700) oxidized under excessive light conditions to alleviate the ROS production. P700 oxidation is universally recognized in photosynthetic organisms as a physiological response to excessive light. However, it is still poorly understood how P700 oxidation is induced in response to fluctuating light with a variety of frequencies. Here, we investigated the relationships of photosynthetic parameters with P700 oxidation in Arabidopsis thaliana under a sine fluctuating light with different frequencies. As the photon flux density of the light increased, P700 was oxidized concurrently with the chlorophyll fluorescence parameter qL unless the electron acceptor side of PSI was limited. Conversely, we did not observe a proportional relationship of non-photochemical quenching with P700 oxidation. The mutant crr-2, which lacks chloroplast NADPH dehydrogenase, was impaired in P700 oxidation during light fluctuation at high, but not low frequency, unlike the pgrl1 mutant deficient in PGR5 and PGRL1 proteins, which could not oxidize P700 during light fluctuation at both high and low frequencies. Taken together, our findings suggested that the changing frequency of fluctuating light reveals the tracking performance of molecular mechanisms underlying P700 oxidation.2018年07月, Plant direct, 2(7) (7), e00073, 英語, 国際誌研究論文（学術雑誌）
- Reactive carbonyls (RCs), which are inevitably produced during respiratory and photosynthetic metabolism, have the potential to cause oxidative damage to photosynthetic organisms. Previously, we proposed a scavenging model for RCs in the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803). In the current study, we constructed mutants deficient in the enzymes medium-chain dehydrogenase/reductase (ΔMDR) and aldo-keto reductase (ΔAKR) to investigate their contributions to RC scavenging in vivo. We found that treatment with the lipid-derived RC acrolein causes growth inhibition and promotes greater protein carbonylation in ΔMDR, compared with the wild-type and ΔAKR. In both ΔMDR and ΔAKR, photosynthesis is severely inhibited in the presence of acrolein. These results suggest that these enzymes function as part of the scavenging systems for RCs in S. 6803 in vivo.Wiley, 2018年03月, FEBS Letters, 592(6) (6), 1010 - 1019, 英語, 国際誌研究論文（学術雑誌）
- To maximize the efficiency of photosynthesis, photosynthetic organisms must properly balance their light-harvesting ability and CO2 utilization. However, the molecular mechanisms of light harvesting under various CO2 conditions remain unclear. To reveal these mechanisms, we performed new analysis on cells of the green alga Chlamydomonas reinhardtii under different CO2 conditions. The analysis combines three kinds of fluorometries: pulse-amplitude modulated fluorescence, steady-state fluorescence with absolute intensity, and time-resolved fluorescence. Under low CO2 conditions, the main regulatory mechanism was migration of a light-harvesting chlorophyll-protein complex (LHC) II from photosystem (PS) II to PSI. However, under CO2-deficient conditions with carbon supplementation, some of the LHCII separated from the PSI and aggregated with quenching. These different light-harvesting abilities of LHCII may play an important role in the regulation of light harvesting in C. reinhardtii under various CO2 conditions.2018年03月, The journal of physical chemistry letters, 9(5) (5), 1028 - 1033, 英語, 国際誌研究論文（学術雑誌）
- Photosynthetic organisms oxidize P700 to suppress the production of reactive oxygen species (ROS) in photosystem I (PSI) in response to the lower efficiency of photosynthesis under high light and low CO2 conditions. Previously, we found a positive relationship between reduction of plastoquinone (PQ) pool and oxidation of P700, which we named reduction-induced suppression of electron flow (RISE). In the RISE model, we proposed that the highly reduced state of the PQ pool suppresses Q-cycle turnover to oxidize P700 in PSI. Here, we tested whether RISE was relieved by the oxidation of the PQ pool, but not by the dissipation of the proton gradient (ΔpH) across the thylakoid membrane. Formation of ΔpH can also suppress electron flow to P700, because acidification on the luminal side of the thylakoid membrane lowers oxidation of reduced PQ in the cytochrome b6/f complex. We drove photosynthetic electron transport using H2O2-scavenging peroxidase reactions. Peroxidase reduces H2O2 with electron donors regenerated along the photosynthetic electron transport system, thereby promoting the formation of ΔpH. Addition of H2O2 to the cyanobacterium Synechococcus elongatus PCC 7942 under low CO2 conditions induced photochemical quenching of chlorophyll fluorescence, enhanced NADPH fluorescence and reduced P700. Thus, peroxidase reactions relieved the RISE mechanism, indicating that P700 oxidation can be induced only by the reduction of PQ to suppress the production of ROS in PSI. Overall, our data suggest that RISE regulates the redox state of P700 in PSI in cooperation with ΔpH regulation.2018年, Frontiers in microbiology, 9, 886 - 886, 英語, 国際誌研究論文（学術雑誌）
- In the light, photosynthetic cells can potentially suffer from oxidative damage derived from reactive oxygen species. Nevertheless, a variety of oxygenic photoautotrophs, including cyanobacteria, algae, and plants, manage their photosynthetic systems successfully. In the present article, we review previous research on how these photoautotrophs safely utilize light energy for photosynthesis without photo-oxidative damage to photosystem I (PSI). The reaction center chlorophyll of PSI, P700, is kept in an oxidized state in response to excess light, under high light and low CO2 conditions, to tune the light utilization and dissipate the excess photo-excitation energy in PSI. Oxidation of P700 is co-operatively regulated by a number of molecular mechanisms on both the electron donor and acceptor sides of PSI. The strategies to keep P700 oxidized are diverse among a variety of photoautotrophs, which are evolutionarily optimized for their ecological niche.2018年, Frontiers in plant science, 9, 1617 - 1617, 英語, 国際誌研究論文（学術雑誌）
- A limitation in carbon dioxide (CO₂), which occurs as a result of natural environmental variation, suppresses photosynthesis and has the potential to cause photo-oxidative damage to photosynthetic cells. Oxygenic phototrophs have strategies to alleviate photo-oxidative damage to allow life in present atmospheric CO₂ conditions. However, the mechanisms for CO₂ limitation acclimation are diverse among the various oxygenic phototrophs, and many mechanisms remain to be discovered. In this study, we found that the gene encoding a CO₂ limitation-inducible protein, ColA, is required for the cyanobacterium Synechococcus sp. PCC 7002 (S. 7002) to acclimate to limited CO₂ conditions. An S. 7002 mutant deficient in ColA (ΔcolA) showed lower chlorophyll content, based on the amount of nitrogen, than that in S. 7002 wild-type (WT) under ambient air but not high CO₂ conditions. Both thermoluminescence and protein carbonylation detected in the ambient air grown cells indicated that the lack of ColA promotes oxidative stress in S. 7002. Alterations in the photosynthetic O₂ evolution rate and relative electron transport rate in the short-term response, within an hour, to CO₂ limitation were the same between the WT and ΔcolA. Conversely, these photosynthetic parameters were mostly lower in the long-term response of a few days in ΔcolA than in the WT. These data suggest that ColA is required to sustain photosynthetic activity for living under ambient air in S. 7002. The unique phylogeny of ColA revealed diverse strategies to acclimate to CO₂ limitation among cyanobacteria.2017年12月, Marine drugs, 15(12) (12), 英語, 国際誌研究論文（学術雑誌）
- In land plants, photosystem I (PSI) photoinhibition limits carbon fixation and causes growth defects. In addition, recovery from PSI photoinhibition takes much longer than PSII photoinhibition when the PSI core-complex is degraded by oxidative damage. Accordingly, PSI photoinhibition should be avoided in land plants, and land plants should have evolved mechanisms to prevent PSI photoinhibition. However, such protection mechanisms have not yet been identified, and it remains unclear whether all land plants suffer from PSI photoinhibition in the same way. In the present study, we focused on the susceptibility of PSI to photoinhibition and investigated whether mechanisms of preventing PSI photoinhibition varied among land plant species. To assess the susceptibility of PSI to photoinhibition, we used repetitive short-pulse (rSP) illumination, which specifically induces PSI photoinhibition. Subsequently, we found that land plants possess a wide variety of tolerance mechanisms against PSI photoinhibition. In particular, gymnosperms, ferns and mosses/liverworts exhibited higher tolerance to rSP illumination-induced PSI photoinhibition than angiosperms, and detailed analyses indicated that the tolerance of these groups could be partly attributed to flavodiiron proteins, which protected PSI from photoinhibition by oxidizing the PSI reaction center chlorophyll (P700) as an electron acceptor. Furthermore, we demonstrate, for the first time, that gymnosperms, ferns and mosses/liverworts possess a protection mechanism against photoinhibition of PSI that differs from that of angiosperms.2017年09月, Physiologia plantarum, 161(1) (1), 56 - 74, 英語, 国際誌研究論文（学術雑誌）
- In higher plants, the electron-sink capacity of photorespiration contributes to alleviation of photoinhibition by dissipating excess energy under conditions when photosynthesis is limited. We addressed the question at which point in the evolution of photosynthetic organisms photorespiration began to function as electron sink and replaced the flavodiiron proteins which catalyze the reduction of O2 at photosystem I in cyanobacteria. Algae do not have a higher activity of photorespiration when CO2 assimilation is limited, and it can therefore not act as an electron sink. Using land plants (liverworts, ferns, gymnosperms, and angiosperms) we compared photorespiration activity and estimated the electron flux driven by photorespiration to evaluate its electron-sink capacity at CO2 -compensation point. In vivo photorespiration activity was estimated by the simultaneous measurement of O2 -exchange rate and chlorophyll fluorescence yield. All C3-plants leaves showed transient O2 -uptake after actinic light illumination (post-illumination transient O2 -uptake), which reflects photorespiration activity. Post-illumination transient O2 -uptake rates increased in the order from liverworts to angiosperms through ferns and gymnosperms. Furthermore, photorespiration-dependent electron flux in photosynthetic linear electron flow was estimated from post-illumination transient O2 -uptake rate and compared with the electron flux in photosynthetic linear electron flow in order to evaluate the electron-sink capacity of photorespiration. The electron-sink capacity at the CO2 -compensation point also increased in the above order. In gymnosperms photorespiration was determined to be the main electron-sink. C3-C4 intermediate species of Flaveria plants showed photorespiration activity, which intermediate between that of C3- and C4-flaveria species. These results indicate that in the first land plants, liverworts, photorespiration started to function as electron sink. According to our hypothesis, the dramatic increase in partial pressure of O2 in the atmosphere about 0.4 billion years ago made it possible to drive photorespiration with higher activity in liverworts.2017年09月, Physiologia plantarum, 161(1) (1), 138 - 149, 英語, 国際誌研究論文（学術雑誌）
- The diffusion efficiency of oxygen in the atmosphere, like that of CO2, is approximately 104 times greater than that in aqueous environments. Consequently, terrestrial photosynthetic organisms need mechanisms to protect against potential oxidative damage. The liverwort Marchantia polymorpha, a basal land plant, has habitats where it is exposed to both water and the atmosphere. Furthermore, like cyanobacteria, M. polymorpha has genes encoding flavodiiron proteins (FLV). In cyanobacteria, FLVs mediate oxygen-dependent alternative electron flow (AEF) to suppress the production of reactive oxygen species. Here, we investigated whether FLVs are required for the protection of photosynthesis in M. polymorpha A mutant deficient in the FLV1 isozyme (ΔMpFlv1) sustained photooxidative damage to photosystem I (PSI) following repetitive short-saturation pulses of light. Compared with the wild type (Takaragaike-1), ΔMpFlv1 showed the same photosynthetic oxygen evolution rate but a lower electron transport rate during the induction phase of photosynthesis. Additionally, the reaction center chlorophyll in PSI, P700, was highly reduced in ΔMpFlv1 but not in Takaragaike-1. These results indicate that the gene product of MpFlv1 drives AEF to oxidize PSI, as in cyanobacteria. Furthermore, FLV-mediated AEF supports the production of a proton motive force to possibly induce the nonphotochemical quenching of chlorophyll fluorescence and suppress electron transport in the cytochrome b6/f complex. After submerging the thalli, a decrease in photosystem II operating efficiency was observed, particularly in ΔMpFlv1, which implies that species living in these sorts of habitats require FLV-mediated AEF.American Society of Plant Biologists ({ASPB}), 2017年03月, Plant physiology, 173(3) (3), 1636 - 1647, 英語, 国際誌研究論文（学術雑誌）
- Photosynthesis produces chemical energy from photon energy in the photosynthetic electron transport and assimilates CO2 using the chemical energy. Thus, CO2 limitation causes an accumulation of excess energy, resulting in reactive oxygen species (ROS) which can cause oxidative damage to cells. O2 can be used as an alternative energy sink when oxygenic phototrophs are exposed to high light. Here, we examined the responses to CO2 limitation and O2 dependency of two secondary algae, Euglena gracilis and Phaeodactylum tricornutum. In E. gracilis, approximately half of the relative electron transport rate (ETR) of CO2-saturated photosynthesis was maintained and was uncoupled from photosynthesis under CO2 limitation. The ETR showed biphasic dependencies on O2 at high and low O2 concentrations. Conversely, in P. tricornutum, most relative ETR decreased in parallel with the photosynthetic O2 evolution rate in response to CO2 limitation. Instead, non-photochemical quenching was strongly activated under CO2 limitation in P. tricornutum. The results indicate that these secondary algae adopt different strategies to acclimatize to CO2 limitation, and that both strategies differ from those utilized by cyanobacteria and green algae. We summarize the diversity of strategies for prevention of photo-oxidative damage under CO2 limitation in cyanobacterial and algal photosynthesis.2017年01月, Scientific reports, 7, 41022 - 41022, 英語, 国際誌研究論文（学術雑誌）
- Diversity in photosynthetic electron transport under [CO2]-limitation: the cyanobacterium Synechococcus sp. PCC 7002 and green alga Chlamydomonas reinhardtii drive an O2-dependent alternative electron flow and non-photochemical quenching of chlorophyll fluorescence during CO2-limited photosynthesis.Some cyanobacteria, but not all, experience an induction of alternative electron flow (AEF) during CO2-limited photosynthesis. For example, Synechocystis sp. PCC 6803 (S. 6803) exhibits AEF, but Synechococcus elongatus sp. PCC 7942 does not. This difference is due to the presence of flavodiiron 2 and 4 proteins (FLV2/4) in S. 6803, which catalyze electron donation to O2. In this study, we observed a low-[CO2] induced AEF in the marine cyanobacterium Synechococcus sp. PCC 7002 that lacks FLV2/4. The AEF shows high affinity for O2, compared with AEF mediated by FLV2/4 in S. 6803, and can proceed under extreme low [O2] (about a few µM O2). Further, the transition from CO2-saturated to CO2-limited photosynthesis leads a preferential excitation of PSI to PSII and increased non-photochemical quenching of chlorophyll fluorescence. We found that the model green alga Chlamydomonas reinhardtii also has an O2-dependent AEF showing the same affinity for O2 as that in S. 7002. These data represent the diverse molecular mechanisms to drive AEF in cyanobacteria and green algae. In this paper, we further discuss the diversity, the evolution, and the physiological function of strategy to CO2-limitation in cyanobacterial and green algal photosynthesis.2016年12月, Photosynthesis research, 130(1-3) (1-3), 293 - 305, 英語, 国際誌研究論文（学術雑誌）
- Oxidation of P700 in Photosystem I Is Essential for the Growth of Cyanobacteria.The photoinhibition of photosystem I (PSI) is lethal to oxygenic phototrophs. Nevertheless, it is unclear how photodamage occurs or how oxygenic phototrophs prevent it. Here, we provide evidence that keeping P700 (the reaction center chlorophyll in PSI) oxidized protects PSI. Previous studies have suggested that PSI photoinhibition does not occur in the two model cyanobacteria, Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942, when photosynthetic CO2 fixation was suppressed under low CO2 partial pressure even in mutants deficient in flavodiiron protein (FLV), which mediates alternative electron flow. The lack of FLV in Synechococcus sp. PCC 7002 (S. 7002), however, is linked directly to reduced growth and PSI photodamage under CO2-limiting conditions. Unlike Synechocystis sp. PCC 6803 and S. elongatus PCC 7942, S. 7002 reduced P700 during CO2-limited illumination in the absence of FLV, resulting in decreases in both PSI and photosynthetic activities. Even at normal air CO2 concentration, the growth of S. 7002 mutant was retarded relative to that of the wild type. Therefore, P700 oxidation is essential for protecting PSI against photoinhibition. Here, we present various strategies to alleviate PSI photoinhibition in cyanobacteria.2016年11月, Plant physiology, 172(3) (3), 1443 - 1450, 英語, 国際誌研究論文（学術雑誌）
- Reduction-Induced Suppression of Electron Flow (RISE) in the Photosynthetic Electron Transport System of Synechococcus elongatus PCC 7942.Accumulation of electrons under conditions of environmental stress produces a reduced state in the photosynthetic electron transport (PET) system and causes the reduction of O2 by PSI in the thylakoid membranes to produce the reactive oxygen species superoxide radical, which irreversibly inactivates PSI. This study aims to elucidate the molecular mechanism for the oxidation of reaction center Chl of PSI, P700, after saturated pulse (SP) light illumination of the cyanobacterium Synechococcus elongatus PCC 7942 under steady-state photosynthetic conditions. Both P700 and NADPH were transiently oxidized after SP light illumination under CO2-depleted photosynthesis conditions. In contrast, the Chl fluorescence intensity transiently increased. Compared with the wild type, the increase in Chl fluorescence and the oxidations of P700 and NADPH were greatly enhanced in a mutant (Δflv1/3) deficient in the genes encoding FLAVODIIRON 1 (FLV1) and FLV3 proteins even under high photosynthetic conditions. Furthermore, oxidation of Cyt f was also observed in the mutant. After SP light illumination, a transient suppression of O2 evolution was also observed in Δflv1/3. From these observations, we propose that the reduction in the plastquinone (PQ) pool suppresses linear electron flow at the Cyt b6/f complex, which we call the reduction-induced suppression of electron flow (RISE) in the PET system. The accumulation of the reduced form of PQ probably suppresses turnover of the Q cycle in the Cyt b6/f complex.2016年07月, Plant & cell physiology, 57(7) (7), 1443 - 1453, 英語, 国内誌研究論文（学術雑誌）
- This study aims to elucidate the molecular mechanism for the transient increase in the O2 -uptake rate in tobacco (Nicotiana tabacum cv Xanthi) leaves after turning off actinic lights (ALs). The photosynthetic O2 evolution rate reaches a maximum shortly after the onset of illumination with ALs and then decreases to zero in atmospheric CO2 /O2 conditions. After turning off the ALs, tobacco leaves show a transient increase in the O2 -uptake rate, the post-illumination transient O2 -uptake, and thereafter, the O2 -uptake rate decreases to the level of the dark-respiration rate. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], maintained a steady-state value distinct from the photosynthetic O2 -evolution rate. In high-[CO2 ] conditions, the photosynthetic O2 -evolution rate and Y(II) showed a parallel behavior, and the post-illumination transient O2 -uptake was suppressed. On the other hand, in maize leaves (a C4 plant), even in atmospheric CO2 /O2 conditions, Y(II) paralleled the photosynthetic O2 -evolution rate and the post-illumination transient O2 -uptake was suppressed. Hypothesizing that the post-illumination transient O2 -uptake is driven by C3 plant photorespiration in tobacco leaves, we calculated both the ribulose 1,5-bisphosphate carboxylase- and oxygenase-rates (Vc and Vo) from photosynthetic O2 -evolution and the post-illumination transient O2 -uptake rates. These values corresponded to those estimated from simultaneous chlorophyll fluorescence/O2 -exchange analysis. Furthermore, the H+ -consumption rate for ATP synthesis in both photosynthesis and photorespiration, calculated from both Vc and Vo that were estimated from chlorophyll fluorescence/CO2 -exchange analysis, showed a positive linear relationship with the dissipation rate of the electrochromic shift signal. Thus, these findings support our hypothesis.2016年02月, Physiologia plantarum, 156(2) (2), 227 - 238, 英語, 国際誌研究論文（学術雑誌）
- 2016年, Photosynthesis Research, 1 - 13, 英語[査読有り]研究論文（学術雑誌）
- This study aims to elucidate the molecular mechanism of an alternative electron flow (AEF) functioning under suppressed (CO2-limited) photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], reaches a maximum shortly after the onset of actinic illumination. Thereafter, Y(II) transiently decreases concomitantly with a decrease in the photosynthetic oxygen evolution rate and then recovers to a rate that is close to the initial maximum. These results show that CO2 limitation suppresses photosynthesis and induces AEF. In contrast to the wild type, Synechocystis sp. PCC 6803 mutants deficient in the genes encoding FLAVODIIRON2 (FLV2) and FLV4 proteins show no recovery of Y(II) after prolonged illumination. However, Synechocystis sp. PCC 6803 mutants deficient in genes encoding proteins functioning in photorespiration show AEF activity similar to the wild type. In contrast to Synechocystis sp. PCC 6803, the cyanobacterium Synechococcus elongatus PCC 7942 has no FLV proteins with high homology to FLV2 and FLV4 in Synechocystis sp. PCC 6803. This lack of FLV2/4 may explain why AEF is not induced under CO2-limited photosynthesis in S. elongatus PCC 7942. As the glutathione S-transferase fusion protein overexpressed in Escherichia coli exhibits NADH-dependent oxygen reduction to water, we suggest that FLV2 and FLV4 mediate oxygen-dependent AEF in Synechocystis sp. PCC 6803 when electron acceptors such as CO2 are not available.2015年02月, Plant physiology, 167(2) (2), 472 - 80, 英語, 国際誌研究論文（学術雑誌）
- In the present paper, we review the toxicity of sugar- and lipid-derived RCs (reactive carbonyls) and the RC-scavenging systems observed in photosynthetic organisms. Similar to heterotrophs, photosynthetic organisms are exposed to the danger of RCs produced in sugar metabolism during both respiration and photosynthesis. RCs such as methylglyoxal and acrolein have toxic effects on the photosynthetic activity of higher plants and cyanobacteria. These toxic effects are assumed to occur uniquely in photosynthetic organisms, suggesting that RC-scavenging systems are essential for their survival. The aldo-keto reductase and the glyoxalase systems mainly scavenge sugar-derived RCs in higher plants and cyanobacteria. 2-Alkenal reductase and alkenal/alkenone reductase catalyse the reduction of lipid-derived RCs in higher plants. In cyanobacteria, medium-chain dehydrogenases/reductases are the main scavengers of lipid-derived RCs.2014年04月, Biochemical Society transactions, 42(2) (2), 543 - 7, 英語, 国際誌研究論文（学術雑誌）
- Sugar-derived reactive carbonyls (RCs), including methylglyoxal (MG), are aggressive by-products of oxidative stress known to impair the functions of multiple proteins. These advanced glycation end-products accumulate in patients with diabetes mellitus and cause major complications, including arteriosclerosis and cardiac insufficiency. In the glycolytic pathway, the equilibration reactions between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (GAP) have recently been shown to generate MG as a by-product. Because plants produce vast amounts of sugars and support the same reaction in the Calvin cycle, we hypothesized that MG also accumulates in chloroplasts. Incubating isolated chloroplasts with excess 3-phosphoglycerate (3-PGA) as the GAP precursor drove the equilibration reaction toward MG production. The rate of oxygen (O2) evolution was used as an index of 3-PGA-mediated photosynthesis. The 3-PGA- and time-dependent accumulation of MG in chloroplasts was confirmed by HPLC. In addition, MG production increased with an increase in light intensity. We also observed a positive linear relationship between the rates of MG production and O2 evolution (R = 0.88; P < 0.0001). These data provide evidence that MG is produced by the Calvin cycle and that sugar-derived RC production is inevitable during photosynthesis. Furthermore, we found that MG production is enhanced under high-CO2 conditions in illuminated wheat leaves.2014年02月, Plant & cell physiology, 55(2) (2), 333 - 40, 英語, 国内誌研究論文（学術雑誌）
- To determine whether alternative electron flow (AEF) can replace the photosynthetic electron flow in cyanobacteria, we used an open O2-electrode system to monitor O2-exchange over a long period. In air-grown Synechocystis sp. PCC 6803 (S. 6803(WT)), the quantum yield of PSII, Y(II), held even after photosynthesis was suppressed by CO2 shortage. The S. 6803 mutant, deficient in flavodiiron (FLV) proteins 1 and 3, showed the same phenotype as S. 6803(WT). In contrast, Y(II) decreased in Synechococcus sp. PCC 7942 (S. 7942). These results suggest that AEF functioned as the Y(II) in S. 6803 and replaced the photosynthetic electron flux. In contrast, the activity of AEF in S. 7942 was lower. The affinity of AEF for O2 in S. 6803 did not correspond to those of FLVs in bacteria or terminal oxidases in respiration. AEF might be driven by photorespiration.2014年, Bioscience, biotechnology, and biochemistry, 78(3) (3), 384 - 93, 英語, 国際誌研究論文（学術雑誌）
- We tested the hypothesis that inducing photosynthesis in cyanobacteria requires respiration. A mutant deficient in glycogen phosphorylase (∆GlgP) was prepared in Synechocystis sp. PCC 6803 to suppress respiration. The accumulated glycogen in ΔGlgP was 250-450% of that accumulated in wild type (WT). The rate of dark respiration in ΔGlgP was 25% of that in WT. In the dark, P700(+) reduction was suppressed in ΔGlgP, and the rate corresponded to that in (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone)-treated WT, supporting a lower respiration rate in ∆GlgP. Photosynthetic O2-evolution rate reached a steady-state value much slower in ∆GlgP than in WT. This retardation was solved by addition of d-glucose. Furthermore, we found that the contents of Calvin cycle intermediates in ∆GlgP were lower than those in WT under dark conditions. These observations indicated that respiration provided the carbon source for regeneration of ribulose 1,5-bisphosphate in order to drive the rapid start of photosynthesis.2014年, Bioscience, biotechnology, and biochemistry, 78(12) (12), 1997 - 2007, 英語, 国際誌研究論文（学術雑誌）
- BACKGROUND: To ensure reliable sources of energy and raw materials, the utilization of sustainable biomass has considerable advantages over petroleum-based energy sources. Photosynthetic algae have attracted attention as a third-generation feedstock for biofuel production, because algae cultivation does not directly compete with agricultural resources, including the requirement for productive land and fresh water. In particular, cyanobacteria are a promising biomass feedstock because of their high photosynthetic capability. RESULTS: In the present study, the expression of the flv3 gene, which encodes a flavodiiron protein involved in alternative electron flow (AEF) associated with NADPH-coupled O2 photoreduction in photosystem I, was enhanced in Synechocystis sp. PCC6803. Overexpression of flv3 improved cell growth with corresponding increases in O2 evolution, intracellular ATP level, and turnover of the Calvin cycle. The combination of in vivo (13)C-labeling of metabolites and metabolomic analysis confirmed that the photosynthetic carbon flow was enhanced in the flv3-overexpressing strain. CONCLUSIONS: Overexpression of flv3 improved cell growth and glycogen production in the recombinant Synechocystis sp. PCC6803. Direct measurement of metabolic turnover provided conclusive evidence that CO2 incorporation is enhanced by the flv3 overexpression. Increase in O2 evolution and ATP accumulation indicates enhancement of the AEF. Overexpression of flv3 improves photosynthesis in the Synechocystis sp. PCC6803 by enhancement of the AEF.2014年, Biotechnology for biofuels, 7(1) (1), 493 - 493, 英語, 国際誌研究論文（学術雑誌）
- Acrolein, an α,β-unsaturated carbonyl, inhibits both growth and PSII activity in the cyanobacterium Synechocystis sp. PCC 6803.In this study, we sought to determine whether and how an α,β-unsaturated carbonyl, acrolein, can inhibit the growth of the cyanobacterium Synechocystis sp. PCC6803 (S. 6803). Treatment of S. 6803 with 200 µM acrolein for 3 d significantly and irreversibly inhibited its growth. To elucidate the inhibitory mechanism, we examined the effects of acrolein on photosynthesis. In contrast to dark conditions, the addition of acrolein to S. 6803 under conditions of illumination lowered the CO₂-dependent O₂ evolution rate (photosynthetic activity). Furthermore, treatment with acrolein lowered the activity reducing dimethyl benzoquinone in photosystem II (PSII). Acrolein also suppressed the reduction rate for the oxidized form of the reaction center chlorophyll of photosystem I (PSI), P700. These results indicate that acrolein inhibited PSII activity in thylakoid membranes. The addition of 200 µM acrolein to the illuminated S. 6803 cells gradually increased the steady-state level (Fs) of Chl fluorescence and decreased the quantum yield of PSII. These results suggested that acrolein damaged the acceptor side of PSII. On the other hand, acrolein did not inhibit respiration. From the above results, we gained insight into the metabolism of acrolein and its physiological effects in S. 6803.2013年, Bioscience, biotechnology, and biochemistry, 77(8) (8), 1655 - 60, 英語, 国際誌研究論文（学術雑誌）
- Functional analysis of the AKR4C subfamily of Arabidopsis thaliana: model structures, substrate specificity, acrolein toxicity, and responses to light and [CO(2)].In Arabidopsis thaliana, the aldo-keto reductase (AKR) family includes four enzymes (The AKR4C subfamily: AKR4C8, AKR4C9, AKR4C10, and AKR4C11). AKR4C8 and AKR4C9 might detoxify sugar-derived reactive carbonyls (RCs). We analyzed AKR4C10 and AKR4C11, and compared the enzymatic functions of the four enzymes. Modeling of protein structures based on the known structure of AKR4C9 found an (α/β)8-barrel motif in all four enzymes. Loop structures (A, B, and C) which determine substrate specificity, differed among the four. Both AKR4C10 and AKR4C11 reduced methylglyoxal. AKR4C10 reduced triose phosphates, dihydroxyacetone phosphate (DHAP), and glyceraldehydes 3-phosphate (GAP), the most efficiently of all the AKR4Cs. Acrolein, a lipid-derived RC, inactivated the four enzymes to different degrees. Expression of the AKR4C genes was induced under high-[CO2] and high light, when photosynthesis was enhanced and photosynthates accumulated in the cells. These results suggest that the AKR4C subfamily contributes to the detoxification of sugar-derived RCs in plants.2013年, Bioscience, biotechnology, and biochemistry, 77(10) (10), 2038 - 45, 英語, 国際誌研究論文（学術雑誌）
- Scavenging systems for reactive carbonyls in the cyanobacterium Synechocystis sp. PCC 6803.To elucidate the scavenging systems of sugar- and lipid-derived reactive carbonyls (RCs) in the cyanobacterium Synechocystis sp. PCC 6803 (S. 6803), we selected proteins from S. 6803 based on amino-acid (AA) sequence similarities with proteins from Arabidopsis thaliana, and characterized the properties of the GST-fusion proteins expressed. Slr0942 catalyzed the aldo-keto reductase (AKR) reaction scavenging mainly sugar-derived RCs, methylglyoxal (MG). Slr1192 is the medium-chain dehydrogenase/redutase (MDR). It catalyzed the AKR reaction scavenging several lipid-derived RCs, acrolein, propionaldehyde, and crotonaldehyde. Slr0315 is a short-chain dehydrogenase/redutase (SDR), and it catalyzed only the reduction of MG in the AKR reaction. Slr0381 catalyzed the conversion of hemithioacetal to S-lactoylglutahione (SLG) in the glyoxalase (GLX) 1 reaction. Sll1019 catalyzed the conversion of SLG to glutathione and lactate in the GLX2 reaction. GLX1 and GLX2 compose the glyoxalase system, which scavenges MG. These enzymes contribute to scavenging sugar- and lipid-derived RCs as scavenging systems.2013年, Bioscience, biotechnology, and biochemistry, 77(12) (12), 2441 - 8, 英語, 国際誌研究論文（学術雑誌）
- 公益社団法人 日本生物工学会, 2024年04月25日, 生物工学会誌, 102(4) (4), 182 - 182, 日本語
- 2023年10月, 光合成研究, 33(2) (2), 107 - 107光合成学会若手の会第26回セミナー開催報告
- 発表要旨日本プランクトン学会, 2022年02月25日, 日本プランクトン学会報, 69(1) (1), 61 - 61, 日本語
- 2022年, 電気化学会大会講演要旨集(CD-ROM), 89thシアノバクテリアSynechocystis sp.PCC 6803の細胞外電子伝達メカニズムの解明
- 一般社団法人 日本土壌肥料学会, 2021年09月03日, 日本土壌肥料学会講演要旨集, 67, 220 - 220, 日本語
- 2021年, 日本植物生理学会年会(Web), 62ndシアノバクテリアにおけるNADP+/NADPHレドックス恒常性の定量的実証
- 2021年, 日本植物生理学会年会(Web), 62ndシアノバクテリアSynechocystis sp.PCC6803の細胞外電子伝達活性は外膜を剥離させることにより向上する
- 2021年, 日本生物工学会大会講演要旨集, 73rdシアノバクテリアにおけるNADP(H)の正確定量
- 2021年, 電気化学秋季大会講演要旨集(CD-ROM), 2021シアノバクテリアSynechocystis sp.PCC6803の外膜剥離による光電流生成能の飛躍的向上
- 東京 : 日本光合成研究会, 2021年, 光合成研究, 31(3) (3), 183 - 185, 日本語若手の会 夏のセミナー「研究者の多様なキャリアパスについて考える。」開催報告会議報告等
- 東京 : 日本光合成研究会, 2020年, 光合成研究, 30(2) (2), 126 - 129, 日本語若手研究者の海外留学レポート第10回「Krieger-Liszkay 研究室@CEA-Saclay (フランス)」記事・総説・解説・論説等（その他）
- 一般社団法人 日本土壌肥料学会, 2019年09月03日, 日本土壌肥料学会講演要旨集, 65, 278 - 278, 日本語
- 一般社団法人 日本土壌肥料学会, 2018年08月29日, 日本土壌肥料学会講演要旨集, 64, 205, 日本語
- 2018年, 光合成研究, 28, 126 - 127First European Congress on Photosynthesis Research, ePS-1会議報告等
- 東京 : 日本光合成研究会, 2017年, 光合成研究, 27(1) (1), 4 - 15, 日本語, 国際共著していない植物が安心して光合成できるワケ～PSIを光傷害から護るP700酸化システム～記事・総説・解説・論説等（その他）
- 2015年, 光合成研究, 25, 221 - 221International Conference “Photosynthesis Research for Sustainability-2015”に参加して会議報告等
- 東京 : 日本光合成研究会, 2015年, 光合成研究, 25(1) (1), 16 - 21, 日本語シアノバクテリアの光合成における酸素利用記事・総説・解説・論説等（その他）
- 2014年, IMARS Highlights, 9, 5 - 13The mechanisms of production and detoxification of dicarbonyls in photosynthetic organisms記事・総説・解説・論説等（国際会議プロシーディングズ）
- 一般社団法人 日本土壌肥料学会, 2013年, 日本土壌肥料学会講演要旨集, 59, 58, 日本語
- 兵庫アグロ・バイオ研究会, 2024年06月植物学者の知らない光合成のお話[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- 応用機能生物セミナー, 2024年05月海で光合成するために公開講演，セミナー，チュートリアル，講習，講義等
- 第65回 日本植物生理学会年会, 2024年Mapping of subcellular local pH in marine diatoms口頭発表（一般）
- Taiwan-Japan Join;Seminar on Photosynthesis Research, 2023年Extra O2 evolution reveals a novel photosynthesis reaction in marine diatoms[招待有り]シンポジウム・ワークショップパネル（指名）
- 8th European Phycological Congress, 2023年Mapping of subcellular local pHs in marine diatoms口頭発表（一般）
- Molecular Life of Diatoms 7, 2023年Pyrenoid-core CO2 evolving machinery is essential for diatom photosynthesis in current and elevated CO2 world口頭発表（一般）
- 第13回 日本光合成学会年会, 2023年海洋性珪藻における細胞内局所pHのマッピングポスター発表
- 第64回 日本植物生理学会年会, 2023年Evolution and diversity of photosynthetic organisms based on the strategy for P700 oxidation[招待有り]シンポジウム・ワークショップパネル（指名）
- International Symposium on Photosynthesis and Chloroplast Regulation, 2022年Photosynthesis in the diatom impaired in chloroplast division口頭発表（一般）
- Journées de la Société Française de Photosynthése, 2022年O2 photoreduction mediated by flavodiiron proteins ~Memory of the collaboration with Dr. Pierre Sétif~[招待有り]口頭発表（招待・特別）
- サンゴ礁生態系におけるレドックスエコバイオロジー, 2022年なぜ褐虫藻はサンゴと共生するのか？口頭発表（一般）
- 日本藻類学会ワークショップ, 2022年光合成解析から見えてくる藻類の多様な生き様[招待有り]シンポジウム・ワークショップパネル（指名）
- 生命科学セミナー, 2021年光合成生物の多様な生き様公開講演，セミナー，チュートリアル，講習，講義等
- 藍藻ゲノム交流会, 2021年藍藻チラコイド膜の電子伝達[招待有り]口頭発表（招待・特別）
- 日本ベントス・プランクトン学会合同大会, 2021年多様な藻類におけるクロロフィル吸収測定法とその応用[招待有り]シンポジウム・ワークショップパネル（指名）
- 電気化学秋季大会, 2021年“生きている光合成”から学ぶこと～光合成の反応制御と活性酸素生成抑制システム～[招待有り]口頭発表（招待・特別）
- 第11回 日本光合成学会年会, 2021年Near‑infrared in vivo measurements of photosystem I and its luminal electron donors with a Klas-NIR spectrophotometer口頭発表（一般）
- 第62回 日本植物生理学会年会, 2021年Regulation of redox state of P700: Damage and protection mechanisms of photosystem I[招待有り]シンポジウム・ワークショップパネル（指名）
- EURAXESS Japan webinar, 2020年Post doc experience in France[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- Seminar organized by Dr. Pierre Cardol, 2020年Mechanisms supporting robust photosynthesis: Diversity and evolution of P700 oxidation system[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- The 84th Annual Meeting of the Botanical Society of Japan, 2020年Revisiting cyclic electron flow in C4 plants[招待有り]シンポジウム・ワークショップパネル（指名）
- パリ若手物理学者 研究者の会, 2019年光合成生物における光傷害とその防御メカニズム: なぜ、私は藻に惹かれるのか？[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- Seminar organized by Dr. Gilles Peltier and Dr. Adrien Burlacot, 2019年Oxidation of P700 ensures robust photosynthesis: How do plants safely do photosynthesis? - Diversity and evolution of P700 oxidation system -[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- Société Française de Photobiologie, 2019年The mechanism in chloroplasts triggering senescence of barley leavesポスター発表
- The 14th Plant Oxygen Group Conference, 2019年The impact of photosynthesis on the initiation of leaf senescence in indoor- and outdoor-grown barleyポスター発表
- Journées de la Société Française de Photosynthése, 2019年In vivo analysis of plastocyanin in senescing barley leaves using a recently-developed near infrared spectrophotometer口頭発表（一般）
- Seminar organized by Dr. Anja Krieger-Liszkay, 2018年Physiological functions of flavodiiron protein: Oxygen is just a by-product in photosynthesis?[招待有り]公開講演，セミナー，チュートリアル，講習，講義等
- Seminar organized by Dr. Chikahiro Miyake, 2018年P700 oxidation is the universal strategy to protect photosystem I against reactive oxygen species also in aquatic phototrophs公開講演，セミナー，チュートリアル，講習，講義等
- Signalisation rétrograde des organites endosymbiotiques, 2018年The mechanism in chloroplasts triggering senescence of barley leavesポスター発表
- The 1th European Congress on Photosynthesis Research, 2018年Changing frequency of fluctuating light reveals the molecular mechanism for P700 oxidation in plant leavesポスター発表
- The 59th Annual Meeting of the Japanese Society of Plant Physiologists, 2018年Diverse strategies to alleviate photo-oxidative damage in photosystem I in cyanobacteria, algae, and plants: A ghost of O2-use in C4 plants口頭発表（招待・特別）
- 第59回 日本植物生理学会年会, 2018年Reduction-induced suppression of electron flow (RISE) is overridden by non-ATP-consuming electron flow in Synechococcus elongatus PCC 7942: P700 oxidation is induced by the reduction of plastoquinone口頭発表（一般）
- The IVth International Conference Molecular Life of Diatoms, 2017年Universality and diversity of P700 oxidation for the protection of photosystem I against ROS-attacks in photosynthetic organisms: Phaeodactylum tricornutum oxidizes P700 without O2-usage口頭発表（一般）
- 第4回 分子珪藻研究会, 2017年微細・大型藻類における活性酸素生成を抑制するための多様な戦略とその進化の足跡～陸上植物が藻類から学んだこと～口頭発表（一般）
- 第58回 日本植物生理学会年会, 2017年基部陸上植物におけるPSI防御戦略: ゼニゴケにおいてFlavodiironタンパク質はP700酸化に働く口頭発表（一般）
- The 17th International Congress on Photosynthesis Research, 2016年Oxidation of P700 in PSI is essential for the growth of cyanobacteriaポスター発表
- Photosynthetic Electron and Proton Transport in Plants and Algae, 2016年Photosynthetic electron and proton transport in the evolutional bridge from algae to plants: Do flavodiiron proteins function in photoprotection in the liverwort Marchantia polymorpha?口頭発表（一般）
- 第3回 分子珪藻研究会, 2016年光化学系Ⅰ防御戦略の多様性～なぜ光合成生物は安全に光合成できるのか？～口頭発表（一般）
- 光合成学会若手の会セミナー, 2016年藍藻におけるP700酸化メカニズムの多様性～なぜP700は酸化される必要があるのか？～[招待有り]シンポジウム・ワークショップパネル（指名）
- 第57回 日本植物生理学会年会, 2016年光合成電子伝達反応の低CO2応答の多様性: O2を使う者と使わざる者口頭発表（一般）
- International Meeting Photosynthesis Research for Sustainability 2015, 2015年Flavodiiron 2 and 4 proteins mediate an O2-dependent alternative electron flow in Synechocystis sp. PCC 6803 under CO2-limited conditions口頭発表（一般）
- 第2回 分子珪藻研究会,, 2015年Diversity of the response of photosynthetic electron transport to low-[CO2]: O2 uses and the use-nots口頭発表（一般）
- 藍藻の分子生物学 2015, 2015年藍藻において暗呼吸は迅速な光合成誘導に不可欠であるポスター発表
- 平成27年度 植物科学談話会, 2015年シアノバクテリアにおけるAlternative electron sinkの生理活性と分子メカニズム公開講演，セミナー，チュートリアル，講習，講義等
- 平成27年度 ラン藻ゲノム交流会, 2015年生理解析から見るラン藻のエレクトロン・シンクの多様性口頭発表（一般）
- 第6回 日本光合成学会年会, 2015年シアノバクテリアにおける光化学系Iの光障害とその防御機構ポスター発表
- 第56回 日本植物生理学会年会,, 2015年Flavodiiron proteins 2 and 4 drive and O2-dependent alternative electron flow to replace photosynthetic linear electron flow in Synechocystis sp. PCC 6803口頭発表（一般）
- Marchantia Workshop 2014, 2014年Glyoxalase system in a liverwort Marchantia polymorpha: A defense system against plant diabetesポスター発表
- PAMを用いた光合成解析技術セミナー, 2014年P700解析の原理とデータの解釈公開講演，セミナー，チュートリアル，講習，講義等
- 第24回 日本メイラード学会, 2014年Production and detoxification mechanisms of methylglyoxal in photosynthetic organisms: Why don’t plant have diabetes?口頭発表（一般）
- 第5回 日本光合成学会年会, 2014年ランソウFlavodiiron proteinによるAlternative electron flowの機能解明とその活性評価ポスター発表
- 日本農芸化学会 2014年度大会, 2014年Scavenging systems for methylglyoxal in the cyanobacterium Synechocystis sp. PCC 6803口頭発表（一般）
- Glyoxalase Centennial: 100 Years of Glyoxalase Research and Emergence of Dicarbonyl Stress, 2013年Production and detoxification mechanisms of methylglyoxal in photosynthetic organisms口頭発表（一般）
- The 16th International Congress on Photosynthesis Research, 2013年Suppression of respiration retard induction of photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803ポスター発表
- 植物生態学・分子生理学コンソーシアムによる陸上植物の高CO2応答の包括的解明 第4回若手ワークショップ, 2013年Scavenging systems for reactive carbonyls in cyanobacterium Synechocystis sp. PCC 6803口頭発表（一般）
■ 共同研究・競争的資金等の研究課題
- 日本学術振興会, 科学研究費助成事業, 学術変革領域研究(A), 関西学院大学, 2024年04月 - 2026年03月光合成指数からみる電子伝達反応制御の多様性と進化
- 日本学術振興会, 科学研究費助成事業 基盤研究(A), 基盤研究(A), 関西学院大学, 2019年04月01日 - 2024年03月31日珪藻ピレノイドの機能から読み解く、海洋二次葉緑体のグローバルインパクト地球一次生産の約20%を担う海洋性珪藻類の生産機能の中心的役割を果たす、葉緑体ピレノイドの構造、機能、およびその地球生態系への影響を見積もることを主眼とし、ゲノム情報および遺伝子改変ツールが整っている海洋性珪藻二種、羽状目Phaeodactylum tricornutumおよび中心目Thalassiosira pseudonanaを用いて研究をすすめた。 ①2019年度に光アミノ酸（PAA）という感光架橋性のジアジリン環を側鎖に持つ人工アミノ酸を用いて、P.tricornutumから単離した新奇ピレノイド構成成分Pyshell、Best、ACCase、およびθ型炭酸脱水酵素（CA）について、2020年度はT.pseudonanaにおいてもそれらの存在を確認した。さらにそれらと相互作用するいくつかの因子を、近位依存性ビオチン標識で選抜し、電気泳動レベルで確認した。さらに②両珪藻におけるこれら因子の局在を、GFPタギングにより標識された融合タンパク質を珪藻細胞内で発現し、確認した。さらに免疫電子顕微鏡観察によっても確認を進めた。③構成成分の発現をRNA干渉、ゲノム編集、および過剰発現技術を用いてかく乱した変異体を引き続き作成し、機能解析に供した。クロロフィル蛍光や酸素発生速度解析による機能解析によって、一部因子の機能推定に至った。また、2019年度終盤に珪藻に対して確立したCRISPR/Cas9ニッカーゼ法を本格的に運用し、多くの変異体選抜を行っている。プロジェクト全体としては、④珪藻葉緑体構造・機能・動態の分子モデル化、および⑤海洋遺伝子動態ビッグデータの解析も試験的行ったが、上記①～③を推進するための変異体取得を中心とした土台固めを本年度は優先的に行い、その成果の一部を国内学会で報告した。④の分子モデル化は、機能推定がなされた因子を順次含める形で徐々に進行しはじめている。
- ひょうご科学技術協会, 学術研究助成, 2023年04月 - 2024年03月, 研究代表者褐虫藻におけるゲノム編集および酸素還元酵素の機能解明
- 日本学術振興会, 科学研究費助成事業 若手研究, 若手研究, 関西学院大学, 2021年04月01日 - 2023年03月31日電気化学を利用した光合成制御リミッターの解除研究実績１：シアノバクテリアSynechocystis sp. PCC 6803において酸化的ペントースリン酸経路(OPPP)がプラストキノンプールの還元に担う役割を明らかにし、その細胞電流への影響を解明した。本課題のねらいは、細胞外電極によるプラストキノンプールの酸化を通して、光合成電子伝達のリミッター(RISE)を解除し、光合成の促進を実現することであるが、課題で対象とする光合成微生物シアノバクテリアではチラコイド膜上に光合成と呼吸、２つの電子伝達系が存在しており、光非依存的なプラストキノンプールの酸化還元を考慮する必要がある。今年度の研究計画を遂行する中で、OPPPがプラストキノンプール還元を主要に担う呼吸関連代謝であることが明らかとなり、またOPPPによるプラストキノン還元が細胞電流の大きさを決める１つの要因であることが分かった。本研究実績は国際学術専門誌Photosynthesis Researchに公表済みである(Hatano et al. 2022 Photosynthesis Research In press, https://doi.org/10.1007/s11120-022-00903-0)。 研究業績２：Synechocystis sp. PCC 6803において光合成、呼吸、サイクリック電子伝達系の活性を半定量的に解析することに成功した。細胞外電極を用いてシアノバクテリアのプラストキノンプール酸化をねらう本申請課題では、チラコイド膜上に存在する各電子伝達系について、その生理活性を大まかに知っておくことが不可欠である。本実績ではグリコールアルデヒドがOPPP阻害剤として働くことを見出し、野生株を用いて光合成、呼吸、サイクリック電子伝達の評価に成功した(Kusama et al. 改訂中)。
- 日本学術振興会, 科学研究費助成事業 特別研究員奨励費, 特別研究員奨励費, 大阪大学, 2020年04月24日 - 2023年03月31日褐虫藻と造礁サンゴの細胞内共生における代替的電子伝達の生理機能本研究では、サンゴに共生する褐虫藻が有する酸素依存的な代替的電子伝達の分子的実体がFlavodiironタンパク質(FLV) であることを見出し、また褐虫藻独自のFLV遺伝子発現様式を発見した。 まず3種のサンゴ共生藻 (褐虫藻) Symbiodinium, Cladocopium, DurusdiniumにおいてcDNAの配列解析を行った。結果として褐虫藻におけるFLVが、他の光合成生物が有する2種のFLV (FLV A/Bペア) の融合タンパク質としてコードされていることを明らかとした。その後、褐虫藻においてFLVが酸素依存的な代替的電子伝達に機能することを調べるため、酸素電極とクロロフィル蛍光測定器を同時に用いることで褐虫藻Cladocopiumの酸素光還元活性を非破壊的に測定するとともに、実際に褐虫藻が共生した造礁サンゴであるミドリイシ (Acropora) を用いて、P700酸化還元の非破壊測定を行った。これら２つの生理解析の実験結果はともに、サンゴに共生した褐虫藻においてFLVによる酸素依存的な代替的電子伝達がP700酸化に貢献している事を支持していた。褐虫藻のもつFLV遺伝子の進化的変遷を明らかにするため、系統解析を行った結果、褐虫藻のFLVが原始緑藻から水平伝播または一過的細胞内共生によって受け継がれていることが示唆された。さらに、実際に生体内で機能しているFLVの分子構造を調べるため褐虫藻のタンパク質を抽出し、免疫染色を行うことで、FLVが一度ポリペプチドとして発現した後、特異的な翻訳後切断によって分裂し、酸素還元に機能することを明らかにした。本研究で得られた成果は、日本植物生理学会年会のシンポジウム「植物レドックス生物学の最前線」において発表しており、また学術雑誌Photosynthesis Researchへ投稿済みである。
- リバネス研究費 PLANTX賞, 2021年04月 - 2022年03月, 研究代表者なぜ野外の植物は老化しても元気なのか？
- 日本学術振興会, 海外特別研究員奨励費, 2018年05月 - 2020年03月, 研究代表者植物における光合成系の発達・衰退を制御するO2利用戦略に関する研究
- 日本学術振興会, 科学研究費助成事業 特別研究員奨励費, 特別研究員奨励費, 神戸大学, 2016年04月22日 - 2018年03月31日光合成生物におけるＦｌａｖｏｄｉｉｒｏｎタンパク質の分子機構と進化的変遷の解明本年度まず申請者は、Flavodiironタンパク質 (FLV) およびFLVに関連した分子メカニズムの反応機構の解明に取り組んだ。まず一年目に大腸菌を用いて作製したFLVリコンビナントタンパク質を用いて、FLVの基質同定を目指した。実験に際しては共発現系を用いる事でFLV1およびFLV3のヘテロダイマーを精製する事に成功し、同時にFLVがホモダイマーではなくヘテロダイマーとして機能する事を支持する結果を得るに至った。当実験によって最終的には、FLVが従来考えられていたNADPHを基質とした酸素の４電子還元を触媒しない事が明らかとなった (Shimakawa et al. 準備中)。さらに申請者は、シアノバクテリアSynechocystis sp. PCC 6803においてFLV2/4と同オペロン上に存在するCO2応答性タンパク質であるColAに着目し、当該タンパク質を独立して保有するSynechococcus sp. PCC 7002を用いる事で、その生理的意義に新たな知見を見出した (Shimakawa et al. 2017 Marine Drugs 15, 390)。 また申請者は、FLVとは異なる光エネルギー散逸機構、つまり活性酸素傷害防御メカニズムとして、シアノバクテリアにおいて呼吸末端酵素が光化学系Iの光傷害緩和に貢献する事を初めて見出した (Shimakawa et al. 2018 Photosynthesis Research in press doi: 10.1007/s11120-018-0495-y) 。 平成29年度を通して申請者は、特別研究員の研究課題に係る3報の筆頭著者論文と1報の共同著者論文を研究業績として上げ、さらに国際分子珪藻学会および日本植物生理学会国際シンポジウムにおいて口頭発表を行った。