Plant salt tolerance

Abstract

Soil salinity adversely affects crop productivity and quality. The success of breeding programs aimed at salinity tolerant crop varieties is limited by the lack of a clear understanding of the molecular basis of salt tolerance. Recent advances in genetic analysis of Arabidopsis mutants defective in salt tolerance, and molecular cloning of these loci, have showed some insight into salt stress signaling and plant salt tolerance. Salt stress-induced cytosolic calcium signals are perceived by SOS3, which is a calcium sensor protein. SOS3 is constitutively myristoylated and associated with the plasma membrane. The SOS3 activates SOS2, a ser/thr protein kinase, in a calcium dependent manner. The active SOS3-SOS2 kinase complex activates SOS1, a Na⁺/H⁺ antiporter on the plasma membrane and also upregulates SOS1 gene expression; this results in Na ⁺ efflux and ion homeostasis. Transgenic analysis showed a tonoplast-located Na⁺/H⁺ antiporter mediates sodium sequestration into the vacuole, and this forms an important part of the salt tolerance mechanism. Evidence also implicates a putative osmosensory histidine kinase (AtHK1)-MAPK cascade and its negative regulators (AtMKP1) in salt stress signaling that probably leads to osmotic homeostasis and ROS scavenging. ABA-mediated regulation of stress proteins and plant growth are also important for plant salt tolerance, but the signaling pathway is poorly understood.