Roles of group 2 sigma factors in acclimation of the cyanobacterium Synechocystis sp. PCC 6803 to nitrogen deficiency
2016
Antal, T. ((University of Turku, Turku (Finland). Department of Biochemistry), (Moscow State University, Moscow (Russia). Biological Faculty)) | Kurkela, J. | Parikainen, M. | Karlund, A. | Hakkila, K. | Tyystjaervi, E. | Tyystjaervi, T.
Acclimation of cyanobacteria to environmental conditions is mainly controlled at the transcriptional level, and sigma factors of the RNA polymerase have a central role in this process. The model cyanobacterium Synechocystis sp. PCC 6803 has four non-essential group 2 sigma factors (SigB, SigC, SigD and SigE) that regulate global metabolic responses to various adverse environmental conditions. Here we show that although none of the group 2 sigma factors is essential for the major metabolic realignments induced by a short period of nitrogen starvation, the quadruple mutant without any group 2 sigma factors and triple mutants missing both SigB and SigD grow slowly in BG-11 medium containing only 5% of the nitrate present in standard BG-11. These deltasigBCDE, deltasigBCD and deltasigBDE strains lost PSII activity rapidly in low nitrogen and accumulated less glycogen than the control strain. An abnormally high glycogen content was detected in deltasigBCE (SigD is active), while the carotenoid content became high in deltasigCDE (SigB is active), indicating that SigB and SigD regulate the partitioning of carbon skeletons in low nitrogen. Long-term survival and recovery of the cells after nitrogen deficiency was strongly dependent on group 2 sigma factors. The quadruple mutant and the deltasigBDE strain (only SigC is active) recovered more slowly from nitrogen deficiency than the control strain, and deltasigBCDE in particular lost viability during nitrogen starvation. Nitrogen deficiency-induced changes in the pigment content of the control strain recovered essentially in 1 d in nitrogen-replete medium, but little recovery occurred in deltasigBCDE and deltasigBDE.
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