Salinity stress in rice: mechanisms and molecular approaches to mitigation

Salinity tolerance in rice is a multilevel trait integrating ion and ROS homeostasis, tissue tolerance, and whole-plant physiology; future breeding requires combining omics-guided selection, genome editing, and field-relevant phenotyping. Salinity stress is one of the extreme abiotic stress factors that reduces rice yield (Oryza sativa L.) and affects about 20% of the worldwide irrigated rice growing area. The present analysis describes the molecular and physiological aspects of salinity tolerance in rice with particular reference to ion homeostasis, osmotic adjustment, and oxidative stress. High-affinity potassium transporters (HKT) and sodium/hydrogen exchangers (NHX) are necessary ion transporters for ion homeostasis in the cell under salt conditions, as ions are abundant outside the cell. However, the rise in reactive oxygen species (ROS) levels and their damaging effects on cellular machinery are suppressed by rice's enzymatic and non-enzymatic antioxidant mechanisms. Producing osmoprotectants such as proline and glycine betaine also assists rice plants in overcoming turgor and protecting protein structures in conditions of osmotic stress. Recent biotechnological practices such as using CRISPR/Cas9 gene editing approaches, transcriptomic research, and epigenetic change-wise phenotypes have opened novel avenues to improve the tolerance of rice plants to soil salinity. At the same time, other challenges exist, such as the polygenic nature of the trait and significant genotype by environmental interactions, which pose serious issues. This review particularly calls for international efforts, through the sharing of knowledge and resources, aimed at developing salt-tolerant rice varieties to prevent food shortages in regions affected by the salinization of soils.