Salt tolerance in rice: Physiological responses and molecular mechanisms

Crop yield loss due to soil salinization is an increasing threat to agriculture worldwide. Salt stress drastically affects the growth, development, and grain productivity of rice (Oryza sativa L.), and the improvement of rice tolerance to salt stress is a desirable approach for meeting increasing food demand. The main contributors to salt toxicity at a global scale are Na+ and Cl− ions, which affect up to 50% of irrigated soils. Plant responses to salt stress occur at the organismic, cellular, and molecular levels and are pleiotropic, involving (1) maintenance of ionic homeostasis, (2) osmotic adjustment, (3) ROS scavenging, and (4) nutritional balance. In this review, we discuss recent research progress on these four aspects of plant physiological response, with particular attention to hormonal and gene expression regulation and salt tolerance signaling pathways in rice. The information summarized here will be useful for accelerating the breeding of salt-tolerant rice.