Heterologous Expression of the Melon CmVQ23 Positively Regulates Resistance to Verticillium dahliae in Arabidopsis

Verticillium dahliae is a devastating soil-borne fungal pathogen that causes severe yield losses in melon (Cucumis melo L.) and other crops. Identifying novel resistance genes is crucial for sustainable disease management. In this study, we characterized the function of CmVQ23, a candidate gene previously identified through QTL mapping, in mediating defense against V. dahliae using heterologous expression in Arabidopsis thaliana. Subcellular localization assays revealed that the CmVQ23-eGFP fusion protein predominantly localized to the nucleus, consistent with its predicted role as a co-factor of transcription factor. Upon V. dahliae inoculation, CmVQ23-overexpressing Arabidopsis lines exhibited significantly reduced disease indices and restricted fungal proliferation compared with wild-type and mutant plants, although these lines displayed altered vegetative growth, including delayed bolting and reduced plant height. Mechanistically, CmVQ23 overexpression promoted reactive oxygen species (ROS) accumulation and hypersensitive response (HR)-mediated cell death at infection sites, as evidenced by intensified DAB and trypan blue staining. Furthermore, transgenic lines maintained higher photosynthetic efficiency, enhanced antioxidant enzyme activities, and increased lignin deposition via upregulation of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO). Notably, CmVQ23 overexpression markedly upregulated both salicylic acid (SA)- and jasmonic acid/ethylene (JA/ET)-responsive marker genes, including AtPR1, AtPR2, AtPR5, AtPAD4, AtPDF1.2, and AtVSP2 upon infection. Collectively, these findings demonstrate that CmVQ23 functions as a positive regulator of resistance to Verticillium dahliae by orchestrating ROS/HR-mediated cell death, antioxidant defense, phenylpropanoid pathway activation, and phytohormone signaling crosstalk, offering a promising genetic resource for improving Verticillium wilt resistance in crops.