Rare alleles from tolerant cultivars are useful for generating salt-tolerant rice

Salinity is a major environmental stress limiting crop yield. The gloomy forecast that by 2025 about 50% of farmland will be severely affected by salinity, coupled with the constantly increasing demand for food, drives home the urgent need to generate salt-tolerant crop plants for ensuring world food security. Salt tolerance is a complex phenomenon regulated by the interplay of multiple genes and factors. Because most of the metabolic activities are sensitive to high levels of Na+ in the cytosol, it is imperative for plants to maintain ion homeostasis in the cells under salt stress. Plants have evolved various adaptive strategies, such as salt exclusion at the roots, salt compartmentation into intracellular compartments, salt secretion at the leaves, and accumulation of excess salt in the older leaves and stems to protect the young photosynthetic leaves, to survive under saline conditions. Plants employ physical barriers (e.g., Casparian strips and suberin lamellae) and ion transporters (e.g., NHXs and SOS pathway) as part of these physiological adaptations. Plants also face the dilemma of trade-off between growth and energy utilization for the adaptive mechanisms under stressed conditions (growth vs. survival). Hence, yield penalty is a major limiting factor encountered during breeding for higher tolerance. Plants employ intricate hormonal crosstalk to overcome abiotic and biotic stresses. Therefore, understanding the associated molecular regulatory mechanisms will facilitate development of elite, stress-tolerant varieties with high yield.