Universal Molecular Triggers of Stress Responses in Cyanobacterium Synechocystis.

Kirill Mironov,Dmitry Los,Maria Shumskaya,Maria Sinetova

doi:10.3390/life9030067

Abstract

Systemic analysis of stress-induced transcription in the cyanobacterium Synechocystis sp. strain PCC 6803 identifies a number of genes as being induced in response to most abiotic stressors (heat, osmotic, saline, acid stress, strong light, and ultraviolet radiation). Genes for heat-shock proteins (HSPs) are activated by all these stresses and form a group that universally responds to all environmental changes. The functions of universal triggers of stress responses in cyanobacteria can be performed by reactive oxygen species (ROS), in particular H2O2, as well as changes in the redox potential of the components of the photosynthetic electron transport chain. The double mutant of Synechocystis sp. PCC 6803 (katG/tpx, or sll1987/sll0755), which is defective in antioxidant enzymes catalase (KatG) and thioredoxin peroxidase (Tpx), cannot grow in the presence of exogenous hydrogen peroxide (H2O2); and it is extremely sensitive to low concentrations of H2O2, especially under conditions of cold stress. Experiments on this mutant demonstrate that H2O2 is involved in regulation of gene expression that responds to a decrease in ambient temperature, and affects both the perception and the signal transduction of cold stress. In addition, they suggest that formation of ROS largely depends on the physical state of the membranes such as fluidity or viscosity. In cyanobacteria, an increase in membrane turnover leads to a decrease in the formation of ROS and an increase in resistance to cold stress. Therefore: (1) H2O2 is the universal trigger of stress responses in cyanobacterial cells; (2) ROS formation (in particular, H2O2) depends on the physical properties of both cytoplasmic and thylakoid membranes; (3) The destructive effect of H2O2 is reduced by increasing of fluidity of biological membranes.

Highlights

Cyanobacteria are oxygenic phototrophic prokaryotes that represent the most ancient group of organisms able to perform oxygenic photosynthesis
SigD regulates the expression of several genes essential for adaptation to oxidative stress induced by high NaCl concentrations [20], and its activity is controlled by a pair of histidine kinase Hik33 and response regulator Rre31 [19]
Hik33 of Synechocystis does not contain amino acid residues that might be oxidized by H2 O2, rather it contains specific light-dependent electron-transport domains PAS and HAMP that might participate in redox-regulated signal transduction [72,73], that are likely to interact with PQ which in turn is sensitive to H2 O2

Summary

Introduction

Cyanobacteria are oxygenic phototrophic prokaryotes that represent the most ancient group of organisms able to perform oxygenic photosynthesis. PCC 6803 (hereafter referred to as Synechocystis) [7] Another histidine kinase, Hik, is involved in regulation of autotrophic growth [8], responses to light [9,10], and resistance to divalent cations (Cd2+ , Cu2+ , and Zn2+ ) [11,12]. Histidine kinase Hik acts as a negative transcriptional regulator during heat shock [13], a positive regulator under salt or hyperosmotic stress, and an autoregulator under oxidative stress [14]. These observations suggest that different stressors may generate some universal intracellular signal(s) that triggers adaptive cell responses. Synechocystis keeping in mind that the discovered patterns can be attributed to other cyanobacterial and bacterial species

Systemic Analysis of Cyanobacterial Stress Transcriptomes

Genes Induced by Heat Stress

Genes Induced by Salt and Hyperosmotic Stress

Genes Induced by Cold Shock and Other Stressors

H2 O2 is Involved in Regulation of Cold Stress Responses

Conclusions