ZmMYC7 negatively regulates salt tolerance in maize through ZmMAPK3-mediated phosphorylation-dependent proteasomal...

Salt stress severely limits maize growth and productivity, yet the molecular mechanisms controlling transcription factor stability during salt stress remain poorly understood. Here, we identified ZmMYC7 as a negative regulator of maize salt tolerance and uncovered its post-translational regulation by ZmMAPK3. ZmMYC7 was rapidly induced by salt stress and localized to the nucleus. CRISPR/Cas9-mediated knockout of ZmMYC7 significantly enhanced salt tolerance, accompanied by reduced membrane damage, lower Na⁺ accumulation, higher K⁺ retention, and improved Na⁺/K⁺ homeostasis under saline conditions. Mechanistically, yeast two-hybrid, bimolecular fluorescence complementation, pull-down, and co-immunoprecipitation assays demonstrated that ZmMAPK3 physically interacts with ZmMYC7 both in vitro and in vivo. In vitro kinase assays further showed that ZmMAPK3 directly phosphorylates ZmMYC7 at Thr367, while phos-tag analysis revealed that salt stress markedly enhances ZmMYC7 phosphorylation in planta. Cell-free degradation assays demonstrated that phosphorylation at Thr367 accelerates the 26S proteasome-dependent degradation of ZmMYC7, thereby reducing its protein abundance. Together, our findings establish a novel ZmMAPK3-ZmMYC7 regulatory module in which salt-induced phosphorylation promotes proteasomal turnover of ZmMYC7, relieving its negative effect on salt tolerance.