GhWRKY39, a member of the WRKY transcription factor family in cotton, has a positive role in disease resistance and salt stress tolerance

WRKY transcription factors have been suggested to play crucial roles in the response to biotic and abiotic stresses. However, previous studies concerning WRKYs have primarily focused on model plants, and fairly limited research has been performed with cotton. In the present study, we functionally characterized a stress-responsive IId WRKY gene (GhWRKY39) from cotton. GhWRKY39 is present as a single copy gene, and subcellular localization analysis indicated that GhWRKY39 localizes to the nucleus. Additionally, some cis-acting elements associated with the environmental stress response were observed in the promoter region of this gene. Consistently, a β-glucuronidase activity assay and quantitative PCR analysis revealed that GhWRKY39 expression could be induced by bacterial and fungal infection or NaCl treatment. Furthermore, the constitutive overexpression of GhWRKY39 in Nicotiana benthamiana conferred greater resistance to bacterial and fungal pathogen infections, and the expression of several pathogenesis-related (PR) genes was significantly increased. The transgenic plants also exhibited less H₂O₂ accumulation than wild-type plants following pathogen infection. Moreover, GhWRKY39-overexpressing plants displayed enhanced tolerance to salt and oxidative stress and increased transcription of antioxidant enzyme genes, including ascorbate peroxidase (APX), catalase (CAT), glutathione-S-transferase (GST) and superoxide dismutase (SOD). Importantly, overexpression of GhWRKY39 improved the activities of the antioxidant enzymes SOD, POD and CAT after pathogen infection and salt stress treatment. Overall, our data suggest that the overexpression of GhWRKY39 may positively regulate the plant response against pathogen infection and salt stress, likely through the regulation of the reactive oxygen species system via multiple signaling pathway.