Coordinated control of calcium signaling by CPK3 and CaM2 via CNGCs in response to cold stress in Arabidopsis

Abstract

Calcium (Ca²⁺) signaling plays a pivotal role in cellular responses to cold stress. Exposure of plant cells to cold water triggers cytosolic Ca²⁺ elevations; however, this treatment may not fully recapitulate Ca²⁺ signal dynamics observed under natural cold stress conditions. In this study, we characterize a distinct Ca²⁺ signal triggered by gradual cooling and demonstrate that CYCLIC-NUCLEOTIDE-GATED CHANNEL 5 (CNGC5) and CNGC6 control this process in plants. Their activities are tightly controlled by CALCIUM-DEPENDENT PROTEIN KINASE 3 (CPK3) and CALMODULIN 2 (CaM2). Cold stress rapidly activates CPK3, which is essential for the activation of CNGC5 and CNGC6 during the initial phases of Ca²⁺ signaling. In contrast, CaM2 negatively controls the activities of CNGC5 and CNGC6 in a Ca²⁺-dependent manner after Ca²⁺ influx. This study demonstrates a previously unidentified mechanism by which the CPK3-CNGC-CaM2 module precisely orchestrates Ca²⁺ signaling dynamics in response to cold stress in Arabidopsis.