D1′—A new member of d1 protein family in cyanobacteria

The D1 protein of Photosystem II (PSII), encoded by the psbA genes, is an indispensable component of oxygenic photosynthesis. Due to strongly oxidative chemistry of PSII water splitting, the D1 protein is prone to constant photodamage requiring its replacement, whereas most of the other PSII subunits remain ordinarily undamaged. In cyanobacteria, the D1 protein is encoded by apsbA gene family, whose members are differentially expressed according to environmental cues. In the recent years many cyanobacterial genomes have been sequenced and are available on the Internet. We have constructed a database of the D1 protein sequences and run several phylogenetic studies in an effort to elucidate the structure of the psbA gene families for those species where the functional studies are missing. Also, we present data regarding the change in psbA gene family expression under environmental stress. A general classification of cyanobacterial D1 isoforms in various cyanobacterial species into D1m, D1:1, D1:2, and D10 forms depending on their expression pattern under acclimated growth conditions and upon stress is discussed, taking into consideration the phototolerance of different D1 forms and the expression conditions of respective members of the psbA gene family.