Mitogen-activated protein kinase 7 phosphorylates transcription factor ZmWRKY104 to enhance salt tolerance in maize

Salt stress is one of the main environmental factors that severely constrain plant growth, development, and productivity. Our recent study showed that the WRKY transcription factor ZmWRKY104 activated ZmSOD4 expression and improved maize salt tolerance. However, the upstream regulator of the ZmWRKY104-ZmSOD4 module in salt response is unknown. Here, we identified a mitogen-activated protein kinase ZmMAPK7, as an upstream regulator of ZmWRKY104 in salt stress response, which physically interacts with ZmWRKY104 in vitro and in vivo. ZmMAPK7 enhances the salt tolerance of maize by increasing superoxide dismutase (SOD) activity to reduce the accumulation of superoxide anion (O2-) generation. Genetic analysis showed that ZmMAPK7 is dependent on ZmWRKY104 in regulating maize salt tolerance. Furthermore, ZmMAPK7 phosphorylates ZmWRKY104 at Ser142, and ZmMAPK7-mediated phosphorylation of ZmWRKY104 enhances its ability to bind to the ZmSOD4 promoter, thereby improving salt tolerance in maize. This study elucidates a novel mechanism by which ZmMAPK7 functions upstream of ZmWRKY104 to positively regulate salt tolerance in maize.