Dual function of VvWRKY18 transcription factor in the β-aminobutyric acid-activated priming defense in grapes.

Induction of phytoalexin production after invading pathogens is recognized as an essential aspect of the plant-induced resistance. The WRKY family includes plant-specific transcriptional factors associated with plant defense responses, but the comprehensive mechanisms are poorly understood. Here, we attempted to elaborate the regulatory function of VvWRKY18 from the group IIa of WRKY transcription factor (TF) from Vitis vinifera, in the regulation of β-aminobutyric acid (BABA)-activated stilbene phytoalexins biosynthesis and PATHOGENESIS-RELATED (PR) genes expressions in grapes. BABA at 10 mmol L-1 triggered a priming protection in grapes and conferred a potentiation of the expression levels of VvWRKY18, VvNPR1, and several salicylic acid (SA)-responsive genes, which was accompanied by enhanced stilbene production upon Botrytis cinerea infection. In addition, a physical interaction between VvWRKY18 and the regulatory protein VvNPR1 was detected in vivo and in vitro by yeast-2-hybrid (Y2H), pull-down and co-immunoprecipitation assay (Co-IP) assays. Furthermore, yeast-1-hybrid (Y1H) and dual-luciferase reporter (DLR) assays indicated that VvWRKY18 activated the transcription of STILBENE SYNTHASE (STS) genes, including VvSTS1 and VvSTS2, by directly binding the W-box elements within the specific promoters and resultantly enhancing stilbene phytoalexins biosynthesis. Further investigation demonstrated that heterologous expression of VvWRKY18 elevated the transcriptions of STS and PR genes, thus contributing to potentiating the defense of transgenic Arabidopsis thaliana plants and resultantly inhibiting B. cinerea invasion. Hence, VvWRKY18 serves as a singular effector involved in the synthesis of stilbene phytoalexins in grapes and its interaction with VvNPR1 provided DNA binding ability required for VvNPR1 to initiate systemic acquired resistance (SAR) defense.