title: 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.
abstract: 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 O2as 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.
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan. gshimakawa@stu.kobe-u.ac.jp.
authors.forename: Ginga
authors.initials: G
authors.lastname: Shimakawa
authors.affiliation: Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.|Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Akimoto
authors.affiliation: Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Ueno
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Wada
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Shaku
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takahashi
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000378:metabolism* / Q000502:physiology; D002734:Chlorophyll / Q000378:metabolism* / Q000502:physiology; D004579:Electron Transport / Q000502:physiology; D005453:Fluorescence; D010788:Photosynthesis / Q000502:physiology; D046940:Synechococcus / Q000378:metabolism* / Q000502:physiology
chemical_list: D002734:Chlorophyll; D002245:Carbon Dioxide
keywords: Alternative electron flow; Non-photochemical quenching; Photosynthetic electron transport; Species diversity