Genome-Wide Identification of the ZF-HD Gene Family in Melon and Functional Characterization of CmZHD8 in Salt Stress Tolerance

Zinc finger homeodomain (ZF-HD) proteins are critical for plant growth, development, and responses to abiotic stress, yet systematic research on the ZF-HD gene family in melon (Cucumis melo L.) remains limited. This study performed a genome-wide characterization of the melon ZF-HD family, followed by functional validation of CmZHD8 under salt stress. Thirteen CmZF-HD genes were identified, unevenly distributed across eight chromosomes, and classified into five subfamilies (ZHD I–IV, MIF), with no ZHD V members, consistent with the classification of cucumber. Family expansion was primarily driven by dispersed and tandem duplication events, with duplicated genes undergoing strong purifying selection (Ka/Ks < 1). Most CmZF-HD promoters contained ABA- and MeJA-responsive cis-acting element and displayed tissue-specific expression patterns. RT-qPCR analysis showed that CmZHD8 expression was sharply induced at 24 h under salt stress, reaching a 26-fold increase over the control, consistent with RNA-seq data. Heterologous expression in yeast confirmed that overexpression of CmZHD8 enhanced salt tolerance. These findings reveal the evolutionary features and functional mechanisms of the CmZF-HD family in salt stress response, identify CmZHD8 as a key candidate gene, and provide a theoretical foundation for stress-resistance research and molecular breeding in melon.