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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.

Cyanobacterial oxygenic photosynthesis transformed the early Earth's biosphere and resulted in complex aerobic life forms. During the course of evolution, cyanobacteria retained many genes that responded to specific environmental cues. Our study shows that microaerobic treatment did not significantly alter the functionality of photosystem II complex in Synechococcus sp. strain PCC 7002. Surprisingly, no changes in the induction levels of psbA genes, especially in D1' isoform, were recorded. This finding is important as signals an atypical behaviour of D1' isoform from Synechococcus sp. PCC 7002 to microaerobic stress as compared to other cyanobacterial strains. [ABSTRACT FROM AUTHOR]

Cyanobacteria, green algae and higher plants have highly conserved photosynthetic machinery. Cyanobacteria have a great plasticity and can be found in different environments, from Arctic zones to hot springs; they can be part of microbial mats. The hot spring near Ciocaia, in Bihor County has a range of different temperatures, from 65.5°C at the spring well, 60.5°C at 2 meters away from the spring well and between 32-38°C in the area where microbial mats are formed. In this study we showed changes in PSII function in mats grown at the location of the hot spring, comparative with microbial mats grown in laboratory conditions. We also showed a comparative study of some basic parameters of chlorophyll fluorescence. These results are very important to understand the functionality of photosystem II in the larger context of adaptation to environmental cues. [ABSTRACT FROM AUTHOR]

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]