Genetic and Physiological Mechanism of Salt Tolerance in Rice: Special Reference to SKC1 and HKT Genes

Abstract

Salt stress poses a significant threat to rice (Oryza sativa L.) production, a staple crop essential for global food security, particularly in Asia where salinity affects vast agricultural lands due to climate change and rising sea levels. This review explores the genetic and physiological mechanisms underlying salt tolerance in rice, with special emphasis on the SKC1 (OsHKT1;5) and HKT gene families. Physiologically, rice maintains Na⁺/K⁺ homeostasis through mechanisms such as sodium exclusion via the SOS pathway, selective K⁺ uptake, vacuolar compartmentalization, osmotic adjustment, and enhanced antioxidant defenses to mitigate reactive oxygen species (ROS)-induced damage. Genetically, key quantitative trait loci (QTLs) like Saltol on chromosome 1, along with genes such as SKC1 and OsHKT1;5, regulate ion transport and exclusion, preventing Na⁺ toxicity in shoots. SKC1 encodes a Na⁺-selective transporter that sustains K⁺/Na⁺ ratios under stress, while HKT transporters facilitate root-shoot Na⁺ partitioning. Breeding strategies, including marker-assisted selection (MAS) for introgressing Saltol and HKT alleles into elite varieties, and biotechnological tools like CRISPR/Cas9 for editing genes such as OsRR22 and DST, have advanced the development of salt-tolerant cultivars. Integrating multi-omics approaches and physiological profiling offers promising avenues for future breeding. This synthesis underscores the interplay between genetics and physiology in enhancing rice resilience, supporting sustainable agriculture in saline environments.