CPK12 decodes effector-triggered calcium signaling and phosphorylates PIP2;1 to facilitate apoplastic ROS transport into the cytoplasm in Arabidopsis.

Effector-triggered immunity (ETI) in plants is mediated by intracellular nucleotide-binding leucine-rich repeat receptors (NLRs), which converge on calcium (Ca) signaling pathways. However, how NLR-induced Ca signals initiate downstream immune responses, such as enhancing reactive oxygen species (ROS) signaling, remains largely unclear. In this study, we identified a calcium-dependent protein kinase (CPK) that regulates sustained ETI-ROS signaling. Upon infection with Pseudomonas syringae pv. tomato (Pst) DC3000 (avrRpm1), CPK12 was activated in a Ca-dependent manner and governed the transport of ETI-ROS from the apoplast to cytoplasm. Both in vitro and in vivo phosphorylation assays revealed that CPK12 phosphorylates the plasma membrane intrinsic protein PIP2;1, thereby enhancing ROS transport and increasing resistance to Pst DC3000 (avrRpm1). Our findings demonstrate that CPK12 deciphers effector-triggered Ca signals to regulate ROS compartmentalization, establishing a crucial link between NLR-mediated Ca signaling and the spatial control of ROS responses in plant immunity.