Multiple ferredoxin isoforms in Chlamydomonas reinhardtii - their role under stress conditions and biotechnological implications.

The unicellular green alga Chlamydomonas reinhardtii has at least six plant-type ferredoxins (FDX). Besides the long-known photosynthetic ferredoxin PetF the isoforms Fdx2-Fdx6 have been identified. The FDX genes are differentially expressed under various environmental conditions such as the availability of oxygen, copper, iron and ammonium. Recently, the anaerobically induced Fdx5 as well as Fdx2, which is involved in nitrite reduction were characterized in more detail. Moreover, it was shown that PetF, the central and most abundant FDX of C. reinhardtii, is a suitable partner of the hydrogenase HydA1. Using mutant variants of both PetF and HydA1, amino acid residues essential for the interaction of both proteins could be identified. These findings will help to tailor PetF for achieving an optimized photobiotechnological hydrogen production in C. reinhardtii, which might also benefit from new insights into the mechanism of how oxygen attacks the active site metal cluster of HydA1. This review gives an update on recent advances in understanding the function of ferredoxins and the hydrogenase in C. reinhardtii.