Dual phosphorylation of StCAMTA3 mediated by distinct calcium sensors orchestrates potato immunity

Plants have evolved a variety of sensors to decode calcium signatures. Precisely decoding calcium signals is essential for plants to thrive in complex environments. However, the underlying mechanism remains elusive. Here, we report that potato calcineurin B-like (CBL)-interacting protein kinase 7 (StCIPK7), a negative regulator in the defense to Phytophthora infestans, interacts with calmodulin-binding transcription activators (StCAMTA3), and directly phosphorylates StCAMTA3 at residue Ser-819. This phosphorylation enhances the transcriptional repression activity of StCAMTA3, thereby promoting plant susceptibility to P. infestans. Notably, upon immune activation, the calcium sensor StCBL3 inhibits StCIPK7-StCAMTA3 interaction as well as the phosphorylation of StCAMTA3 by StCIPK7, thereby relieving the repression of defense-responsive gene expression mediated by StCAMTA3 and enhancing disease resistance. Moreover, we demonstrated that another type of calcium sensor, StCPK5, phosphorylates and destabilizes StCAMTA3. Collectively, our findings define a two-tiered calcium sensor-controlled mechanism for plant defense against P. infestans.