Pumpkin CmoCDPK20 improved the salt tolerance of grafted cucumber by phosphorylating CmoDREB2A to promote jasmonic acid biosynthesis and antioxidant enzyme activities

Soil salinization hinders crop growth, but salt-tolerant pumpkin is a valuable rootstock for grafting cucumbers. Calcium-dependent protein kinases (CDPKs) play an important role in plant salt tolerance, yet their specific functions in pumpkin and the underlying mechanisms regulating salt tolerance remain largely unknown. In this study, we identified CmoCDPK20 as a key regulator of salt tolerance in pumpkin and grafted cucumber. Functional characterization revealed that CmoCDPK20 enhanced the salt tolerance of grafted cucumbers by inducing jasmonic acid (JA) biosynthesis and antioxidant enzyme activities. Mechanistic investigations demonstrated that CmoCDPK20 interacts with and phosphorylates the transcription factor dehydration-responsive element-binding protein 2A (CmoDREB2A) at Ser241/396 residues. The activated CmoDREB2A subsequently binds to the promoters of CmoAOC2, CmoPOD2, and CmoCAT3, leading to increased JA production and antioxidant enzyme activity. These findings elucidate a novel regulatory pathway underlying salt tolerance in pumpkin and provide insights for developing salt-tolerant pumpkin rootstocks.