Reference : A Chlamydomonas mutant locked in anaerobiosis
Scientific congresses and symposiums : Unpublished conference/Abstract
Life sciences : Biochemistry, biophysics & molecular biology
A Chlamydomonas mutant locked in anaerobiosis
Ghysels, Bart mailto [Université de Liège - ULg > > Labo de Bioénergétique >]
Matagne, René-Fernand mailto [Université de Liège - ULg > Services généraux (Faculté des sciences) > Relations académiques et scientifiques (Sciences) >]
Franck, Fabrice mailto [Université de Liège - ULg > > Labo de Bioénergétique >]
Colloque annuel de la Société Française de Photosynthèse
16-17 mai 2011
Société Française de Photosynthèse
[en] Photosynthesis ; Hydrogenase ; Chlamydomonas
[en] The soil dwelling microalga Chlamydomonas reinhardtii most likely encounters transient periods of anaerobiosis in its natural environment, for instance at night time or when photosynthesis is turned down in response to macronutrient limitation. Anoxic conditions trigger state I to state II transition in C.r. and the induction of a chloroplast hydrogenase., which ability to accept electrons from reduced Fd results in a transient light driven H2 evolution. We present evidence that hydrogenase induction and state transitions are required for the induction of photosynthesis in anaerobiosis and therefore critical for this alga in order to survive transient anaerobic periods in the dark. In an anaerobic metabolic context the induction of photosynthesis is severely slowed down. The highly reduced state of the NAD(P) pools and the absence of O2 as electron sink hamper light driven reoxydation of the intersystem electron carriers while CO2 assimilation by the Calvin cycle is inhibited by ATP deficiency. We have seen that gradual increase of hydrogenase activity during anaerobiosis restores a PSI acceptor pool and leads to a reduction of the induction lag of oxygenic photosynthesis. A mutant HydEF devoid of hydrogenase maturation genes typically shows 3 to 4 times longer lag phases that the WT. State transitions provide another mechanism by which photosynthetic electron transport can be unlocked in anaerobic conditions. A state II conformation is known to stimulate photo-phosphorylation, and may therefore restore Calvin cycle activity in an ATP depleted metabolic context. We observed that an anaerobically adapted stt7 mutant locked in state I is only able to induce oxygenic photosynthesis upon hydrogenase expression. We therefore constructed a double mutant Stt7HydEF impaired of state transition ability and hydrogenase activity and found it to have lost the capacity of inducing photosynthesis in anaerobic conditions.
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