Identification of an R2R3 MYB transcription factor involved in the regulation of the stilbene synthase pathway in grapevine

Stilbene synthases (STSs) are a class of enzymes belonging to the general CHS type III polyketide synthase family involved in the last step of the biosynthesis of stilbenes. These enzymes, and their main products resveratrol or pynosylvin are detectable in only a limited number of unrelated plant species, including grape, and accumulate in response to biotic and abiotic stresses. Despite numerous studies that have been performed on the accumulation, metabolism and biological properties of resveratrol, little is known about the transcriptional regulation of this pathway. Based on mRNA-sequencing data obtained from grapevine leaf discs treated with biotic and abiotic stresses we identified a candidate R2R3 MYB transcription factor that shows an expression pattern similar to that observed for STS genes and could to be involved in their regulation in grape. This R2R3 MYB factor was designated VvMYB14, based on homology with the AtMYB14 R2R3 MYB factor. Neither gene has previously been functionally characterized in either plant species. Analysis of VvMYB14 expression in grape leaf discs treated with biotic (downy mildew infection) and abiotic stresses (wounding and UV-C exposure) known to be involved in the transcriptional activation of VvSTS genes, showed a close correlation between the pattern and timing of expression of selected VvSTS genes and VvMYB14. Using a Dual Luciferase Reporter Assay System in transiently transformed grapevine cells, VvMYB14 was also demonstrated to increase stilbene synthase promoter activity. Confirmation of the role of VvMYB14 in the trans-activation of VvSTS genes in-planta is currently being examined using a transgenic grapevine hairy root system for testing the effect of both silencing and over expression of VvMYB14 on the response of VvSTS expression.