CALCIUM-DEPENDENT PROTEIN KINASE9 negatively regulates cold tolerance by phosphorylating the NADPH oxidase VpRBOHD in grapevine

Calcium-dependent protein kinases (CPKs) are key regulators of plant responses to abiotic stress; however, their roles in grapevine under cold stress remain poorly understood. In this study, we demonstrate that cold-repressed VpCPK9 and its counterpart NADPH oxidase VpRBOHD negatively regulate cold tolerance in grapevine. VpCPK9 interacts with VpRBOHD and phosphorylates VpRBOHD at Ser33, Ser132, and Ser138. This phosphorylation enhances VpRBOHD stability, thereby promoting reactive oxygen species (ROS) production under cold conditions, leading to reduced cold tolerance of grapevine. Our study reveals a negative role of the VpCPK9-VpRBOHD module in grapevine cold response and provides candidate genes for improving cold tolerance through genome editing.