Genome-wide association study reveals that the SUS domain protein SS7 positively regulates seed storability in rice (Oryza sativa L.).

Abstract

Key message: The rice seed storability gene Seed storability 7 (SS7) encodes a cytosol localized sucrose synthase (SUS) domain protein. SS7 positively regulates seed storability by enhancing the activity of peroxidase and nitrate reductase (NR) in seeds, resulting in the reduction of ROS and NO accumulation during seed storage. Long-term storage of crop seeds is essential for conserving germplasm resources, ensuring food security, and supporting sustainable agriculture. In this study, we characterized the function of Seed storability 7 (SS7), the causal gene for the QTL qSS7-1 responsible for rice seed storability identified by genome-wide association studies (GWAS). SS7 encodes a cytosol localized sucrose synthase (SUS) domain protein. Overexpression of SS7 significantly enhanced seed storability under both artificial and natural aging conditions. While knockout of SS7 has no significant effects in seed storability, but showed a phenotype of enhanced elongation of rice root. Transcriptome analysis revealed that differentially expressed genes (DEGs) involving in the hydrogen peroxide (H₂O₂) catabolic pathway were significantly enriched in SS7 overexpression lines; in contrast, the DEGs in both H₂O₂ catabolism and nitric oxide (NO) biosynthesis pathways were enriched in SS7 knockout lines. Furthermore, ROS accumulated significantly in SS7 knockout seeds, whereas SS7 overexpression in seeds resulted in a significant enhancement of peroxidase activity and a significant reduction in nitrate reductase (NR) activity, compared to SS7 knockout seeds. These results suggested that SS7 enhances seed storability by reducing the accumulation of peroxides, but inhibits root elongation by promoting NO accumulation, of which provides new insights into understanding the molecular mechanisms of rice seed storability.