Stress responses of Synechocystis sp. strain PCC 6803 mutants impaired in genes encoding putative alternative sigma factors

Abstract

In the complete genome sequence of the cyanobacterium Synechocystis sp. strain PCC 6803 [Kaneko et al. (1996). DNA Res 3, 109-136] genes were identified encoding putative group 3 σ-factors SigH (Sll-0856), SigG (Slr-1545) and SigF (Slr-1564) and the regulatory protein RsbU (Slr-2031). Mutations in these genes were generated by interposon mutagenesis to study their importance in stress acclimation. For the genes sigH, sigF and rsbU, the loci segregated completely. However, attempts to mutagenize the sigG locus resulted in merodiploids. Under standard growth conditions only minor differences were detected between the mutants and wild-type. However, cells of the RsbU mutant showed a clear defect in regenerating growth after a nitrogen-and sulphur-starvation-induced stationary phase. After applying salt, heat and high-light shocks, stress protein synthesis was analysed by means of one-and two-dimensional electrophoresis. Cells of the SigF mutant showed a severe defect in the induction of salt stress proteins. Although the acclimation to moderate salt stress up to 684 mM NaCl was not significantly changed in this mutant, its ability to acclimate to higher concentrations of NaCl was reduced. Northern blot experiments showed a constitutive expression of the rsbU and sigF genes. The expression of the sigH gene was found to be stressstimulated, particularly in heat-shocked cells, whilst that of sigG was transiently decreased under stress conditions. Possible functions of these regulatory proteins in stress acclimation of Synechocystis cells are discussed.

The SigB σ Factor Regulates Multiple Salt Acclimation Responses of the Cyanobacterium Synechocystis sp. PCC 6803

“…Many His kinases (Shoumskaya et al, 2005), three group 2 s factors SigB, SigC, and SigE (Pollari et al, 2008), two group 3 s factors (Huckauf et al, 2000;Marin et al, 2002), and a transcriptional repressor protein, GppR (Klähn et al, 2010) have been identified as potential regulators of salt acclimation of Synechocystis cells. Figure 9 summarizes salt acclimation processes that are at least partly regulated by the SigB factor.…”

Acclimation of unicellular cyanobacteria to macronutrient deficiency: emergence of a complex network of cellular responses

“…The presence of a PAS domain in NblS suggests that light or redox changes may serve as a trigger for this pathway (van Waasbergen et al, 2002). An additional modulator of general acclimation responses may be the protein encoded by slr2031, a homologue of eubacterial regulators of s B ; cultures of an slr2031 mutant exhibit a lower proportion of cells capable of resuming growth following nitrogen or sulfur starvation (Huckauf et al, 2000).…”

Group 3 sigma factors in the marine cyanobacterium Synechococcus sp. strain PCC 7002 are required for growth at low temperature

“…strain PCC 7002 (Fig. 6), but since the sigG gene cannot be inactivated by interposon mutagenesis (Huckauf et al, 2000), it has been concluded to be essential in Synechocystis sp. strain PCC 6803 under optimal growth conditions.…”

“…The sigF (slr1564) gene is shown to be required for biosynthesis of pili and motility of the cells (Bhaya et al, 1999) and the induction of salt stress proteins (Huckauf et al, 2000). The sigG (slr1545) gene is apparently essential for cell viability in this cyanobacterium (Huckauf et al, 2000). Although transcripts of these group 3 sigma factor genes are detectable, the amounts of the proteins in cells are less than the detection limits by immunoblot analysis (Imamura et al, 2003b).…”

“…strain PCC 6803, in which four group 3 sigma factor genes have been found based upon the complete genome sequencing analysis (Kaneko et al, 1996). The sigF (slr1564) gene is shown to be required for biosynthesis of pili and motility of the cells (Bhaya et al, 1999) and the induction of salt stress proteins (Huckauf et al, 2000). The sigG (slr1545) gene is apparently essential for cell viability in this cyanobacterium (Huckauf et al, 2000).…”