Brassinosteroids improve nitrogen utilization by antagonizing BIN2-mediated SnRK1 activation

Nitrogen is an essential nutrient for plant growth and development, and is central to increasing crop yield. Brassinosteroids (BRs) and their analogs are widely used in agriculture to enhance crop yields and improve nitrogen utilization, yet the underlying mechanism remains fragmentary. Here, we demonstrate that BR conservatively improves nitrogen utilization by modulating the activity of SnRK1, an evolutionarily conserved regulator balancing carbon and nitrogen metabolism. Exogenous BR application increases plant biomass and nitrogen utilization, and enhances key nitrogen assimilation enzyme activities when photosynthesis is inhibited. Metabolomic reveals that BR restores 47.8% of metabolic alterations caused by photosynthetic suppression. Mechanistically, BIN2, a key kinase in BR signaling, interacts with and phosphorylates KIN10, the catalytic α-subunit of SnRK1, at conserved Thr175 and Ser179, thereby stabilizing KIN10. BR inhibits BIN2, promoting KIN10 degradation and thereby activating nitrate-responsive gene expression and enhancing nitrogen assimilation. These findings reveal how BR signaling enhances nitrogen utilization and offer insights for improving crop productivity and sustainability. Brassinosteroids are widely used in agriculture, but their modes of action remain incompletely understood. Here, the authors show that brassinosteroids inhibit BIN2, leading to KIN10 degradation and activation of gene expression and nitrogen assimilation enzymes.