Interplay between glutathione and mitogen-activated protein kinase 3 via transcription factor WRKY40 under combined osmotic and cold stress in Arabidopsis

Glutathione (GSH) plays a fundamental role in plant defense. Recent reports showed that enhanced GSH content activates mitogen-activated protein kinases (MPKs). However, the molecular mechanism behind this GSH-mediated MPKs expression during environmental challenges is unexplored. Here, we found that under control and combined abiotic stress-treated conditions, GSH feeding activates MPK3 expression in Arabidopsis thaliana by inducing its promoter, as established through the promoter activation assay. Additionally, transgenic A. thaliana overexpressing the LeMPK3 gene (AtMPK3 line) showed increased γ-ECS expression, which was decreased in mpk3, the MPK3-depleted mutant. An in-gel kinase assay exhibited hyperphosphorylation of Myelin Basic Protein (MBP) in the GSH-fed AtMPK3 transgenic line. Under control and combined abiotic stress treated conditions, expression of transcription factor WRKY40 binding to MPK3 promoter was up-regulated under enhanced GSH condition. Interestingly, GSH feeding was rendered ineffective in altering MPK3 expression in the Atwrky40 mutant, emphasizing the involvement of WRKY40 in GSH-MPK3 interplay. This was further confirmed by a wrky40 co-transformation assay. The immunoprecipitation assay followed by ChIP-qPCR showed a significant increase in the binding of WRKY40 to MPK3 promoter, which further established MPK3-WRKY40 association upon GSH feeding. In conclusion, this study demonstrated that GSH modulates MPK3 expression via WRKY40 in response to stress.