The PsaE subunit of photosystem I prevents light-induced formation of reduced oxygen species in the cyanobacterium Synechocystis sp. PCC 6803.
The PsaE protein is located at the reducing side of photosystem I (PSI) and is involved in docking the soluble electron acceptors, particularly ferredoxin. However, deletion of the psaE gene in the cyanobacterium Synechocystis sp. strain PCC 6803 inhibited neither photoautotrophic growth, nor in vivo linear and cyclic electron flows. Using photoacoustic spectroscopy, we detected an oxygen-dependent, PSI-mediated energy storage activity in the DeltapsaE null mutant, which was not present in the wild type (WT). The expression of the genes encoding catalase (katG) and iron superoxide dismutase (sodB) was upregulated in the DeltapsaE mutant, and the increase in katG expression was correlated with an increase in catalase activity of the cells. When catalases were inhibited by sodium azide, the production of reactive oxygen species was enhanced in DeltapsaE relative to WT. Moreover, sodium azide strongly impaired photoautotrophic growth of the DeltapsaE mutant cells while WT was much less sensitive to this inhibitor. The katG gene was deleted in the DeltapsaE mutant, and the resulting double mutant was more photosensitive than the single mutants, showing cell bleaching and lipid peroxidation in high light. Our results show that the presence of the PsaE polypeptide at the reducing side of PSI has a function in avoidance of electron leakage to oxygen in the light (Mehler reaction) and the resulting formation of toxic oxygen species. PsaE-deficient Synechocystis cells can counteract the chronic photoreduction of oxygen by increasing their capacity to detoxify reactive oxygen species.
Jeanjean
Robert
R
Laboratoire de Chimie Bactérienne, CNRS-UPR 9043, Institut de Biologie Structurale et Microbiologie, 31 chemin Joseph Aiguier, F-13402 Marseille cedex 20, France.
Latifi
Amel
A
Matthijs
Hans C P
HC
Havaux
Michel
M
D002374:Catalase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D004579:Electron Transport / Q000528:radiation effects; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000378:metabolism; D007700:Kinetics; D008027:Light; D015227:Lipid Peroxidation / Q000528:radiation effects; D009154:Mutation; D018384:Oxidative Stress / Q000187:drug effects / Q000528:radiation effects*; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects*; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D019810:Sodium Azide / Q000494:pharmacology; D013057:Spectrum Analysis; D013482:Superoxide Dismutase / Q000096:biosynthesis; D046939:Synechocystis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects*
D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D045331:Photosystem I Protein Complex; D017382:Reactive Oxygen Species; C079741:photosystem I, psaE subunit; D019810:Sodium Azide; D002374:Catalase; D013482:Superoxide Dismutase