The autophagy-related protein OsCOST1 negatively regulates the salt tolerance in rice

The autophagy-related protein COST1 (constitutively stressed 1) is essential for the normal growth and response to abiotic stress via modulating the autophagy pathway in plants. However, the biological functions of COST family proteins in graminaceous crops like rice in response to salt stress remain uncharacterized. Here, OsCOST1 RNAi lines were generated. Knockdown of OsCOST1 expression enhanced the salt tolerance of transgenic plants, as shown by alleviated growth inhibition in them. The increased salt tolerance was accompanied by increased proline accumulation, elevated antioxidant enzyme activity, up-regulated stress-responsive gene expression and improved K⁺/Na⁺ homeostasis in transgenic plants. Yeast two-hybrid and BiFC assays demonstrated that OsCOST1 interacted with OsATG8 autophagy proteins. Monodansylcadaverine (MDC) staining showed that the autophagy activity was significantly improved, as exhibited by increased autophagosome formation, in transgenic plants when grown under salt stress conditions. Nonsynonymous single-nucleotide polymorphism (SNP) screening in the OsCOST1 gene across 202 rice varieties indicated that natural variation in the coding sequence was closely associated with their divergences in salt tolerance. Our study on the interplay between autophagy and environmental stress could offer a strategic insight into the breeding of new salt-tolerant rice varieties.