The ZmRACK1–ZmCDPK7–ZmAPX1 module regulates plant antiviral immunity

Calcium-dependent protein kinases (CDPKs) in plants play crucial roles in mediating responses to both biotic and abiotic stresses. However, the molecular mechanism through which CDPKs regulate antiviral immunity in plants remains largely elusive. In this study, we identified ZmCDPK7 as a key player in response to various stimuli. Lines overexpressing ZmCDPK7 exhibited enhanced resistance to maize chlorotic mottle virus (MCMV) infection, while ZmCDPK7 knock-out lines demonstrated increased sensitivity, indicating that ZmCDPK7 positively regulates maize immunity against MCMV. Furthermore, ZmCDPK7 interacts with ZmAPX1 and enhances its enzymatic activity by phosphorylating ZmAPX1 at Thr164, thereby reducing reactive oxygen species (ROS) production. The scaffold protein ZmRACK1 interacts with both ZmCDPK7 and ZmAPX1, facilitating the formation of a ternary complex that enhances ZmCDPK7-mediated ZmAPX1 enzymatic activity. Lines overexpressing ZmAPX1 also showed increased resistance to MCMV infection, while ZmAPX1 mutant lines (Zmapx1 MU1 and Zmapx1 MU2) exhibited increased sensitivity. Additionally, CRISPR/Cas9-mediated genome editing of ZmRACK1 in maize resulted in increased susceptibility to MCMV. To counteract plant defense, the MCMV protein P31 interacts with ZmCDPK7 and ZmRACK1, disrupting the interaction between ZmRACK1-ZmCDPK7 and ZmCDPK7-ZmAPX1, thereby blocking the ternary complex formation. Moreover, ZmCDPK7 is also implicated in defense against drought stress and corn stalk rot. Overall, our findings provide valuable insights into the molecular mechanisms by which the ZmRACK1-ZmCDPK7-ZmAPX1 module regulates plant immunity, identifying the potential new targets for the genetic control of maize viral diseases.