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

Abstract

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.