Salt stress response in Rice (Oryza sativa ssp. japonica): a focus on glutathione and sulphur metabolism

Increasing soil salinization poses a significant challenge to global agriculture, necessitating the identification of crop varieties with enhanced salt tolerance. This study investigates the phenotypic and molecular salt-stress response of four Italian rice varieties, Baldo, Onice, Selenio, and Vialone Nano, showing dissimilar susceptibility to salinity, aiming to identify molecular traits related to plant tolerance toward soil salinization. Phenotypic evaluations revealed Baldo and Onice as the most tolerant varieties while Selenio and Vialone Nano exhibited greater susceptibility. The different phenotypes observed after salt exposure were consistent with distinct patterns of reactive oxygen species (ROS) and antioxidant responses observed in the four rice varieties subjected to salt stress. These different biochemical responses were underpinned by the up-regulation of critical genes involved in glutathione biosynthesis and sulphur assimilation, which led to elevated glutathione levels in the stress-tolerant varieties of rice. Consequently, this caused a more pronounced rise in the antioxidant shield of the tolerant varieties compared to the sensitive ones. Moreover, a more detailed molecular investigation of the mechanisms possibly regulating sulphur metabolism revealed that epigenetic differences in sulphur-related genes highlighted potential heritable mechanisms of stress tolerance. In addition, tolerant varieties exhibited faster and more effective miR395-mediated post- translational regulation of key sulphur genes compared to sensitive ones, ensuring their efficient sulphur assimilation and glutathione production. Therefore, the findings reported in this study provide valuable insights into the physiological, molecular, and epigenetic mechanisms of salt tolerance in rice.