Abstract
The structural differences of MYB14 promoter in two grapevine genotypes affect the expression of MYB14 and stilbene synthesis in response to Al3+ and UV-C radiation. Grapevines provide an important fruit crop worldwide, but production is often limited by pathogen infection. Stilbenes, a class of secondary metabolite, represent phytoalexins that contribute to defence against pathogens in many plants, including grapevine. It is known that the transcription factors MYB14 and MYB15 are required for the activation of the promoters of resveratrol synthase to regulate stilbene biosynthesis. In the current study, we observed that stilbene levels were more highly induced by Al3+ and UV-C radiation treatments in the cultivar Vitis labrusca 'Concord' than in the cultivar V. vinifera 'Cabernet Sauvignon'. We investigated whether genetic/structural variations in the MYB14 and MYB15 promoters between these two representative genotypes are responsible for the differences in stilbene accumulation. Significant differences in the structure and activity of the promoter of MYB14, but not MYB15 were identified between the two genotypes, following heterologous expression in Nicotiana benthamiana system and treatments with Al3+ and UV-C. Hydrogen peroxide (H2O2) was detected in Concord soon after the stress treatments, but after diphenyleneiodonium chloride pre-treatment, the expressing level of VlMYB14, the promoter activity of VlMYB14 and the accumulation of stilbenes was significantly reduced. A model is presented where the induction of MYB14 contributes to stilbene accumulation in Concord following Al3+ and UV-C treatments involving reactive oxygen species (ROS) production as an early signal.