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In almost all cyanobacteria a small gene family encodes the photosystem II reaction center D1 proteins that play vital roles in the cell. Recently, several types of this protein were functionally characterised and the conditions for their transcript regulation were identified. One of the D1-encoding genes previously believed to be silent is induced by microaerobic conditions. This gene was first described in Synechocystis sp. PCC 6803 as psbA1 encoding the D1 isoform. When Synechocystis cells are shifted from high to ambient level CO2 we recorded an increase in gene expression, similar, but to a lesser extent, to microaerobic conditions. When synthetic air is used to remove the ambient CO2, the induction of the gene is absent. We documented for the first time that expression of a psbA gene is regulated by the inorganic carbon status of the cell. Our conclusion is that both CO2 and microaerobic conditions are independently influencing the expression of psbA1 gene in Synechocystis sp. PCC 6803. Hence, it is crucial to understand the mechanisms of regulation and function of D1 proteins as it could be used for future bio-technological applications as a virtual tool-box for modulating the function of PSII. more...

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 damage and requires its replacement by a new copy every 5 h under low light conditions and every 20 minutes under intense illumination, whereas most of the other PSII subunits remain ordinarily undamaged. In cyanobacteria the D1 protein is encoded by a psbA gene family, ranging from 1 to 6 members. The presence of multiple psbA genes encoding different D1 isoforms is an indication of their importance in regulatory mechanisms responsible for maintaining a functional PSII upon changing environmental conditions in natural habitats of cyanobacteria. Herewith, we present a comparative analysis of the protein sequences encoded by psbA gene family in model cyanobacteria strains with sequenced genomes, highlighting their characteristic features that give indication of their putative function. [ABSTRACT FROM AUTHOR] more...