Multi-omics approach reveals the contribution of brassinosteroids to salt tolerance for seed germination in rice

Seed germination initiates the plant life cycle, but it exhibits high sensitivity to salt stress, which is a significant environmental factor limiting rice production. Brassinosteroid (BR) is a growth-promoting phytohormone that mitigates various stresses in rice including salt, drought, and extreme temperatures. However, the mechanisms by which BR alleviates salt stress during seed germination remain inadequately characterized. This study demonstrates that seed-specific overexpression of OsDWF4, a rate-limiting gene in BR biosynthesis, enhances rice germination. The DWF4-OX lines, which have greater endogenous BR content in the seeds, showed better germination under salt stress, corroborating the results obtained through exogenous BR application. Antioxidant enzyme analyses demonstrated that BR enhances the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Metabolomic analysis revealed that BR mitigates salt stress primarily through the biosynthesis of phenylpropanoids and secondary metabolites. Transcriptomic analysis indicated that both endogenous and exogenous BR share five co-regulated target genes and utilize a common biosynthetic pathway for stilbenoids, diarylheptanoids, and gingerols. These findings confirm the capacity of BR to enhance seed germination under salt stress and identified several BR-mediated targets for developing salt-tolerant rice varieties that are suitable for direct seeding cultivation.