Light-regulation of photosystem I reaction centre genes in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Light-intensity- and light-quality-dependent changes in the expression of the psaAB operon, encoding the photosystem I (PSI) reaction centre heterodimer, were studied in the cyanobacterium Synechocystis sp. PCC 6803. Transfer of the cells from growth light to darkness, or to higher irradiances, induced down-regulation of psaAB transcription. Similar down-regulation could also be induced under growth light by chemically blocking the photosynthetic electron flow, or by illuminating the cells under PSI-light. PSII-light, on the contrary, stimulated the transcription of the psaAB operon. These results suggest that the redox state of an intersystem redox component plays a role in the regulation of psaAB transcription. However, the slow activation of psaAB transcription upon transfer of dark-treated cells back to the light points to the existence of yet another, a more general transcriptional regulation, which may be related to the production of new PSI centres during growth. In addition to the transcription, also the stability of the psaA/B transcripts responded to the intersystem redox state. The present study indicates that the synthesis of PSI during acclimation to the prevailing light conditions is not only regulated at translational and post-translational levels, as reported earlier, but also at the level of psaAB gene transcription and transcript stability.