OsGSK2‐OsTCP19 Module Integrates Nitrogen and Brassinosteroid Signaling to Regulate Nitrogen Utilization and Root Growth in Rice

Nitrogen (N) and brassinosteroids (BRs) are key regulators of plant developmental plasticity in fluctuating nutrient environments, yet the direct molecular link coordinating these two signaling pathways remains elusive. Here, we report a synergistic interplay between nitrate and BR signaling that governs N utilization and lateral root development in rice (Oryza sativa L.). Nitrate activates BR response in a dose-dependent manner, with maximal induction at 2.5 mM nitrate. Conversely, activated BR signaling enhances nitrate signaling and lateral root elongation, which strictly depends on the protein level of OsTCP19, a negative regulator of root growth. Nitrate-induced BR signaling promotes OsTCP19 degradation within 2-4 h, while the BR signaling core kinase OsGSK2 interacts with and phosphorylates OsTCP19 at Ser141 and Thr289 to stabilize its protein. OsTCP19 directly binds to the promoters of nitrate-responsive genes (e.g., OsNRT2.4, OsNADH-GOGAT1, OsASN1) and root development genes (e.g., OsIAA3, OsPIN1b, OsARF19) to negatively regulate N responses and lateral root growth, respectively. Together, the OsGSK2-OsTCP19 module establishes a direct molecular link between nitrate and BR signaling, coordinating N utilization and root plasticity in rice.