Salt- and Osmo-Responsive Sensor Histidine Kinases Activate the General Stress Response to Initiate Functional Symbiosis.

The general stress response (GSR) enables bacteria to sense and overcome a variety of environmental stresses. In alphaproteobacteria, stress-perceiving histidine kinases of the HWE and HisKA_2 families trigger a signaling cascade that leads to phosphorylation of the response regulator PhyR and, consequently, to activation of the GSR σ factor σ. In the nitrogen-fixing bacterium , PhyR and σ are crucial for tolerance against a variety of stresses under free-living conditions and also for efficient infection of its symbiotic host soybean.