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In response to the ratio of available carbon (C) and nitrogen (N) nutrients,plants regulate their metabolism,growth,and development,a process called the C/N-nutrient response.However,the molecular basis of C/N-nutrient signaling remains largely unclear.In this study,we identified three CALCINEURIN B-LIKE (CBL)-INTERACTING PROTEIN KINASES (CIPKs),CIPK7,CIPK12,and CIPK14,as key regulators of the C/N-nutrient response during the post-germination growth in Arabidopsis.Single-knockout mutants of ClPK7,ClPK12,and CIPK14 showed hypersensitivity to high C/low N conditions,which was enhanced in their triple-knockout mutant,indicating that they play a negative role and at least partly function redundantly in the C/N-nutrient response.Moreover,these ClPKs were found to regulate the function of ATL31,a ubiquitin ligase involved in the C/N-nutrient response via the phosphorylation-dependent ubiquitination and proteasomal degradation of 14-3-3 proteins.ClPK7,ClPK12,and CIPK14 physically interacted with ATL31,and CIPK14,acting with CBL8,directly phosphorylated ATL31 in a Ca2*-dependent manner.Further analyses showed that these CIPKs are required for ATL31 phosphorylation and stabilization,which mediates the degradation of 14-3-3 proteins in response to C/N-nutrient conditions.These findings provide new insights into C/N-nutrient signaling mediated by protein phosphorylation.