CIPK11 Regulates Plant Adaptation to Nitrate Availability in Arabidopsis.

Nitrate (NO3-) is an essential nitrogen source and an important signaling molecule that regulates plant growth and development in response to nitrogen availability. Although several CBL-interacting protein kinases (CIPKs) have been implicated in nitrate signaling, the role of CIPK11 (PKS5) in nitrate availability responses remains unknown. Here, we investigated the function of CIPK11 using Arabidopsis mutants under nitrate-deficient and nitrate-resupply conditions by analyzing growth phenotypes, nitrate and protein accumulation, nitrate-responsive gene expression, extracellular H+ dynamics, and responses to the plasma membrane (PM) H+-ATPase inhibitor protonstatin-1 (PS-1). CIPK11 expression was downregulated under nitrate deficiency and rapidly induced after nitrate resupply. The loss-of-function mutant pks5-1 exhibited enhanced growth, increased nitrate and protein accumulation, and stronger induction of nitrate-responsive genes (NRT2.1, NRT2.4, NIA1, and NIA2), whereas the gain-of-function mutants pks5-3 and pks5-4 showed opposite phenotypes. Altered extracellular H+ dynamics and PS-1 sensitivity further suggested that PM H+-ATPase activity contributes to CIPK11-mediated nitrate responses. Collectively, our findings identify CIPK11 as a negative regulator of plant adaptation to nitrate availability and suggest that CIPK11 modulates nitrate acquisition and assimilation, at least partly through regulation of PM H+-ATPase activity.