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

: Nikkinen HL, Häkkilä K, Gunnelius L, Huokko T, Pollari M, Tyystjärvi T

Publisher: AMER SOC PLANT BIOLOGISTS

: 2012

: Plant Physiology

: PLANT PHYSIOLOGY

: PLANT PHYSIOL

: 1

: 158

: 1

: 514

: 523

: 10

: 0032-0889

DOI: https://doi.org/10.1104/pp.111.190058

: http://dx.doi.org/10.1104/pp.111.190058

Changing of principal sigma factor in RNA polymerase holoenzyme to a group 2 sigma factor redirects transcription when cyanobacteria acclimate to suboptimal environmental conditions. The group 2 sigma factor SigB was found to be important for the growth of the cyanobacterium Synechocystis sp. PCC 6803 in high-salt (0.7 M NaCl) stress but not in mild heat stress at 43 degrees C although the expression of the sigB gene was similarly highly, but only transiently up-regulated at both conditions. The SigB factor was found to regulate many salt acclimation processes. The amount of glucosylglycerol-phosphate synthase, a key enzyme in the production of the compatible solute glucosylglycerol, was lower in the inactivation strain Delta sigB than in the control strain. Addition of the compatible solute trehalose almost completely restored the growth of the Delta sigB strain at 0.7 M NaCl. High-salt conditions lowered the chlorophyll and phycobilin contents of the cells while protective carotenoid pigments, especially zeaxanthin and myxoxanthophyll, were up-regulated in the control strain. These carotenoids were up-regulated in the Delta sigCDE strain (SigB is the only functional group 2 sigma factor) and down-regulated in the Delta sigB strain under standard conditions. In addition, the HspA heat shock protein was less abundant and more abundant in the Delta sigB and Delta sigCDE strains, respectively, than in the control strain in high-salt 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.