From UVR 8 to flavonol synthase: UV ‐ B ‐induced gene expression in S auvignon blanc grape berry

The aim of this research was to determine the effect of development and UV ‐ B on flavonols and the regulation of gene activity in V itis vinifera   L . var. S auvignon blanc grapes. Particular emphasis was placed on gene activity associated with the low and high fluence UV ‐ B responses. Flavonols, particularly quercetin and kaempferol glycosides, increased substantially upon fruit exposure due to UV ‐ B , with spatial analysis locating the changes to the berry skin. Of five VvFLS genes in grapes, two ( VvFLS4 and 5 ) were found to be transcriptionally active, with VvFLS4 also being responsive to UV ‐ B but VvFLS5 was not. Of the transcription factors known to regulate FLS ( VvMYB12 , VvMYCA1 and VvWDRs ), only VvMYB12 was found to be responsive to UV ‐ B . A number of candidate genes associated with the low and high UV ‐ B fluence responses were also studied ( VvUVR8 , VvHY5 , VvCOP1 and VvCHS ; PR genes and VvMAPK3 ; respectively). The genes associated with the low fluence response exhibited transcriptional regulation in line with reports from other species, while the PR genes and VvMAPK3 only appeared to be responsive in a high UV ‐ B fluence environment. Together, these data supports the view flavonol biosynthesis in grape is stimulated predominantly through the low fluence UV ‐ B response pathway.