Over-expression of a grape WRKY transcription factor gene, VlWRKY48, in Arabidopsis thaliana increases disease resistance and drought stress tolerance

Members of the plant WRKY transcription factor family play important roles in regulating response to various biotic and abiotic stresses. A previous gene expression study suggested that the grape gene, WRKY48, was up-regulated during drought stress and fungal infection, as well as in response to exogenous addition of plant hormones. To examine this relationship in more details, we over-expressed VlWRKY48 from V. labrusca x V. vinifera (cv. Kyoho) in Arabidopsis thaliana. Root length and the rate of seed germination were greater in three transgenic lines than that in wild type (WT) plants, the seedlings and adult plants displayed fewer stress-related symptoms following drought treatment than WT, in addition to lower water loss rate. Moreover, over-expression of VlWRKY48 resulted in an increase in the activities of the antioxidant enzymes of catalase, peroxidase and superoxide dismutase after drought treatment, as well as in the expression of several stress-related genes. We also observed that the VlWRKY48 over-expressing lines exhibited higher resistance to powdery mildew, as evidenced by fewer disease symptoms and an increased expression of defense-related genes following infection. Taken together, the results suggest that VlWRKY48 regulates a range of responses to drought stresses, and enhances resistance to powdery mildew infection.