title: Ca(2+)-regulated cyclic electron flow supplies ATP for nitrogen starvation-induced lipid biosynthesis in green alga.
abstract: We previously showed that both the linear photosynthetic electron transportation rate and the respiration rate dropped significantly during N starvation-induced neutral lipid accumulation in an oil-producing microalga, Chlorella sorokiniana, and proposed a possible role for cyclic electron flow (CEF) in ATP supply. In this study, we further exploited this hypothesis in both Chlorella sorokiniana C3 and the model green alga Chlamydomonas. We found that both the rate of CEF around photosystem I and the activity of thylakoid membrane-located ATP synthetase increased significantly during N starvation to drive ATP production. Furthermore, we demonstrated that the Chlamydomonas mutant pgrl1, which is deficient in PGRL1-mediated CEF, accumulated less neutral lipids and had reduced rates of CEF under N starvation. Further analysis revealed that Ca(2+) signaling regulates N starvation-induced neutral lipid biosynthesis in Chlamydomonas by increasing calmodulin activity and boosting the expression of the calcium sensor protein that regulates Pgrl1-mediated CEF. Thus, Ca(2+)-regulated CEF supplies ATP for N starvation-induced lipid biosynthesis in green alga. The increased CEF may re-equilibrate the ATP/NADPH balance and recycle excess light energy in photosystems to prevent photooxidative damage, suggesting Ca(2+)-regulated CEF also played a key role in protecting and sustaining photosystems.
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Jinlu
authors.initials: J
authors.lastname: Hu
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Yaqin
authors.initials: Y
authors.lastname: Qiao
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Weixian
authors.initials: W
authors.lastname: Chen
authors.affiliation: SINOPEC Research Institute of Petroleum Processing, Beijing, China.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Rong
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Yunming
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
authors.forename: Chenliu
authors.initials: C
authors.lastname: He
authors.affiliation: Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
mesh_terms: D025181:ATP Synthetase Complexes / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D002708:Chlorella / Q000145:classification / Q000235:genetics / Q000378:metabolism; D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport / Q000235:genetics / Q000502:physiology; D015151:Immunoblotting; D008055:Lipids / Q000096:biosynthesis*; D018613:Microscopy, Confocal; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics / Q000502:physiology; D045331:Photosystem I Protein Complex / Q000378:metabolism; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D020524:Thylakoids / Q000201:enzymology / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D008055:Lipids; D045331:Photosystem I Protein Complex; D000255:Adenosine Triphosphate; D002374:Catalase; D013482:Superoxide Dismutase; D025181:ATP Synthetase Complexes; D009584:Nitrogen; D002118:Calcium