Alcohol dehydrogenase and hydrogenase transcript fluctuations during a day/night cycle in Chlamydomonas reinhardtii: the role of anoxia.

The unicellular green alga Chlamydomonas reinhardtii contains two iron (Fe)-hydrogenases which are responsible for hydrogen production under anoxia. In the present work the patterns of expression of alcohol dehydrogenase, a typical anaerobic gene in plants, of the hydrogenases genes (HYD1, HYD2) and of the genes responsible for their maturation (HYDEF, HYDG), were analysed. The expression patterns were analysed by real-time reverse-transcription polymerase chain reaction in Chlamydomonas cultures during the day–night cycle, as well as in response to oxygen availability. The results indicated that ADH1, HYD1, HYD2, HYDEF and HYDG were expressed following precise day–night fluctuations. ADH1 and HYD2 were modulated by the day–night cycle. Low oxygen plays an important role for the induction of HYD1, HYDEF and HYDG, while ADH1 and HYD2 expression was relatively insensitive to oxygen availability. The regulation of the anaerobic gene expression in Chlamydomonas is only partly explained by responses to anoxia. The cell cycle and light–dark cycles are equally important elements in the regulatory network modulating the anaerobic response in Chlamydomonas.