As the addition from the compatible solute trehalose nearly completely restored the growth from the sigB strain at high-salt stress, it could be a low amount from the GgpS enzyme, specifically in the beginning of the sodium stress, may be the major reason why sigB cells acclimate only extremely slowly to high-salt stress. low in the inactivation stress sigB than in the control stress. Addition from the suitable solute trehalose nearly totally restored the development from the sigB stress at 0.7mNaCl. High-salt circumstances reduced the chlorophyll and phycobilin items from the cells while defensive carotenoid pigments, specifically zeaxanthin and myxoxanthophyll, had been up-regulated in the control stress. These carotenoids were up-regulated in the sigCDE strain (SigB is the only functional group 2 factor) and down-regulated in the sigB strain under standard conditions. In addition, the HspA heat shock protein was less abundant and more abundant in the sigB and sigCDE strains, respectively, than in the control strain in high-salt (+)-α-Lipoic acid conditions. Some cellular responses are common to heat and salt stresses, but pretreatment with mild heat did not protect cells against salt shock although protection against heat shock was evident. Different cyanobacterial species have adapted to ecological niches varying from fresh water to hypersaline environments. Research of salt acclimation is important because large-scale cultivation of cyanobacteria, for example for bioenergy production, would best occur in brackish water or seawater, as fresh water supplies of the Earth are limited. Salt acclimation processes in cyanobacteria are already fairly well known (for recent review, seeHagemann, 2011) but the sensing and transmission of salt signals are not yet well understood. Salt stress acclimation and signaling processes are best characterized in a model cyanobacteriumSynechocystissp. strain PCC 6803 (hereafterSynechocystis).Synechocystisis a unicellular, nontoxic, nonnitrogen-fixing freshwater cyanobacterium that is moderately halotolerant. Salt acclimation in cyanobacteria occurs in five phases (Hagemann, 2011). A salt shock causes rapid shrinking of the cells due to loss of water (Blumwald et al., 1983) via aquaporins (Shapiguzov et al., 2005). In the second phase, ions including Na+and Clpassively enter the cells and water flows back to the cells (Reed et al., 1985) but cellular processes including photosynthesis (Allakhverdiev et al., 2000) and gene expression (Hagemann et al., 1994;Fulda et al., 2006) remain slow due to high ion (especially (+)-α-Lipoic acid Na+) content of the cells. The third phase is characterized by an exchange of Na+to K+that allows the reactivation of photosynthesis, and the beginning of synthesis of compatible solutes (Reed et al., 1985). InSynechocystis, as in many other moderately halotolerant species, the main compatible solute is glucosylglycerol (Hagemann, 2011). Salt addition activates an inactive form of glucosylglycerol-phosphate synthase, and also enhances the transcription of theggpSgene encoding glucosylglycerol-phosphate synthase (Marin et al., 2002;Stirnberg et al., 2007;Hagemann, 2011;Novak et al., 2011). In the fourth phase, typically occurring 2 to 12 h after the onset Mouse monoclonal to EphB6 of salt stress, compatible solutes accumulate to such high concentrations that they are mainly responsible for the maintenance of the osmotic potential. In this phase, also the gene expression pattern changes (Hagemann et al., 1994;Marin et al., 2004;Fulda et al., 2006) to finally allow full acclimation to (+)-α-Lipoic acid high-salt conditions, which is the fifth phase. The actual mechanism of salt sensing is still unclear. InSynechocystis, transcriptome analyses with His kinase/response regulator mutants have revealed that at least Hik33/Rre31, Hik34/Rre1, Hik2/Rre1, Hik16/Hik41/Rre17, and Hik10/Rre3 participate, but any of these regulators could be inactivated without great impact on growth in salt stress conditions, suggesting functional redundancy (Shoumskaya et al., 2005). Furthermore, these regulators are involved in other stresses like osmotic, oxidative, or heat stress (Paithoonrangsarid et al., 2004;Shoumskaya et al., 2005;Suzuki et al., 2005;Kanesaki et al., 2007). The microarray technique has revealed that several hundred genes are up- or down-regulated during salt acclimation, many of them encoding proteins with unknown function (Kanesaki et al., 2002;Marin et al., 2004;Fulda et al., 2006). Highly activated genes include genes encoding enzymes involved in osmolyte synthesis and transport, ion transporters, and common stress proteins like heat shock proteins and Hlips (Marin et al., 2004). The actual regulatory mechanisms remain to be solved. In cyanobacteria, the central role of group 2 factors in acclimation to many suboptimal environmental conditions has been noticed (for review, seeOsanai et al., 2008). Many subunits of the RNA polymerase holoenzyme might be involved in adjustments of gene expression during salt acclimation. Inactivation of the group 2 factor SigB leads to a salt-sensitive phenotype, and also the sigC and sigE strains grow slowly after addition of 0.7mNaCl (Pollari et al., 2008). Furthermore, inactivation of the group 3 factor (+)-α-Lipoic acid SigF delayed the activation of theggpsgene and the accumulation of glucosylglycerol (Marin et al., 2002). A specific repressor protein, GppR, that suppresses the expression of theggpSgene under low-salt conditions was recently discovered (Klhn et al., 2010). In this study, we focused on the role of the SigB factor in salt acclimation processes by comparing the factor inactivation.
