OsNRT1.1B‐OsCNGC14/16‐Ca 2+ ‐OsNLP3 Pathway: Phosphorylation‐Mediated Maintenance of Nitrogen Homeostasis

Abstract Nitrate, a crucial nutrient and signaling molecule, is extensively studied across plants. While the NRT1.1‐NLP‐centered pathway dominates nitrate signaling in Arabidopsis and rice, however, whether there is functional interaction or co‐regulation between the primary nitrate response (PNR) and long‐term nitrogen utilization remains unclear. Here, a novel nitrate signaling pathway is identified in rice that works alongside the established ubiquitination‐mediated OsNRT1.1B‐OsSPX4‐OsNLP3 cascade. It is demonstrated that OsCNGC14, OsCNGC16, and OsNRT1.1B form a plasma membrane‐localized complex in root tips, mediating nitrate‐triggered Ca 2 ⁺ influx. The absence of either OsCNGC14 or OsCNGC16 abolished Ca 2 ⁺ signaling and suppressed PNR. The OsNRT1.1B‐OsCNGC14/16 complex activates Ca 2 ⁺‐dependent phosphorylation of OsNLP3 at Ser193, which accelerates its nuclear translocation and transcriptional activation of nitrate‐responsive genes. This phosphorylation enhances both short‐term PNR and long‐term nitrogenutilization. This findings reveal a dual regulatory network in rice: the Ca 2 ⁺‐OsNLP3 pathway rapidly amplifies nitrate signals, while the ubiquitination‐mediated OsSPX4 degradation ensures sustained nitrogen homeostasis.