HvMAPK5‐Mediated Phosphorylation of HvWRKY75 Enhances Salt Tolerance in Barley

ABSTRACT Soil salinization is a significant constraint on crop productivity, necessitating the elucidation of the molecular mechanisms underlying salt tolerance in cereals such as barley. In this study, a novel regulatory module comprising the ion transporter HvHKT1;2 , the transcription factor HvWRKY75 , and the mitogen‐activated protein kinase HvMAPK5 was identified. HvHKT1;2 localized to the plasma membrane, and its overexpression promoted Na + efflux at the root apex, reduced Na + accumulation in shoots, increased the K + /Na + ratio, and enhanced salt tolerance, whereas HvHKT1;2 knockdown produced the opposite phenotype. Furthermore, HvWRKY75 directly bound to the HvHKT1;2 promoter and activated its transcription. Under salt stress, HvMAPK5 interacted with and phosphorylated HvWRKY75 at Ser21, thereby enhancing HvWRKY75 protein stability and transcriptional activity toward HvHKT1;2. Consistently, HvMAPK5 overexpression increased HvWRKY75 protein abundance, upregulated HvHKT1;2 expression, and enhanced salt tolerance, whereas HvMAPK5 knockdown accelerated HvWRKY75 degradation and compromised salt tolerance. Collectively, our findings identify a regulatory module consisting of HvMAPK5 , HvWRKY75 , and HvHKT1;2 that maintains cellular Na + /K + homeostasis during salt stress, providing a mechanistic framework for breeding salt‐tolerant barley varieties.