Effect of solar ultraviolet radiation on grape berry skin transcriptome. Vitis vinifera

UV radiation (UV) alters secondary metabolism in the skin of Vitis vinifera L. berries, which may affect on the final composition of both, grapes and wines. We compared berry skin transcriptome and phenolic composition between Tempranillo berries grown in the presence or absence of solar UV in a mid-altitude Tempranillo vineyard. By analysing two different ripening degrees, expression of 121 genes was significantly altered. Functional enrichment identified that, principally, secondary metabolism-related transcripts were induced by UV, including VvFLS1, VvGT5 and VvGT6 flavonol biosynthetic genes induction. Concurrently, flavonol accumulation was the most evident impact of UV on the berry skin phenolic composition. Monoterpenoid biosynthetic transcripts were also up-regulated by UV, whereas induction of stilbenoid biosynthetic transcripts and stilbenes accumulation was probably induced by the joint action of UV and other condition under the UV-blocking filter, likely higher temperature. Among regulatory genes, VvMYBF1, VvMYB24 and three bHLH transcription factors were up-regulated by UV. Homologs to Arabidopsis UVR8-dependent UV-B-induced genes were also induced, including VvHY5-1, VvHY5-2 and VvRUP UV-B signalling genes. This suggests that the UV-B-specific signalling pathway is activated in the skin of grapes grown at low-medium altitudes. The biosynthesis and accumulation of UV-absorbing compounds that are appreciated for winemaking were almost specifically triggered, which indicates that viticultural practices increasing solar UV incidence may improve grape features important to wine production. Overall design: A total of 12 samples were hybridized. Grape skin RNA from berries ripening under a UV-transmitting filter (FUV+) and a UV-blocking filter (FUV-) was compared. Berry skin of two different ripening stages was analysed on each UV treatment. All samples were harvested simultaneously and a NaCl series was used to select the ripening degree in a non-invasive way. Three biological replicates were analyzed for each sample.