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Light promotes expression of monoterpene and flavonol metabolic genes and enhances flavour of winegrape berries (Vitis vinifera L. cv. Riesling)

Friedel, M., Frotscher, J., Nitsch, M., Hofmann, M., Bogs, J., Stoll, M., Dietrich, H.
Australian journal of grape and wine research 2016 v.22 no.3 pp. 409-421
Vitis vinifera, biochemical pathways, biosynthesis, cultivars, flavonols, flavor, gene expression, genes, glycosyltransferases, monoterpenoids, odors, quantitative polymerase chain reaction, ripening, small fruits, solar radiation, wine grapes, wines
BACKGROUND AND AIMS: Insolation of grape bunches has long been postulated to enhance the flavour of aromatic grape cultivars. This hypothesis was tested by combining gene expression and metabolic analysis of the monoterpene and flavonol synthesis pathways. METHODS AND RESULTS: Grape bunches were shaded or shaded and reilluminated to investigate the influence of light on the monoterpene and flavonol biosynthetic pathways. The expression of terpenoid and flavonol metabolic genes was measured by quantitative polymerase chain reaction under light and shade conditions during the ripening phase and compared to the accumulation of their respective metabolic products. Expression of flavonol synthase and flavonol glycosyltransferase genes was virtually absent in shaded bunches, but expression increased strongly upon reillumination, as did the flavonol content of the berries. The expression of the terpene synthase genes as well as the monoterpene content were greatly reduced in shaded bunches, and then increased upon reillumination. The expression of terpene glycosyltransferases was affected only slightly by light. CONCLUSIONS: The results of this study show the positive influence of light on monoterpene and flavonol biosynthesis. SIGNIFICANCE OF THE STUDY: Optimising the light exposure of grape berries enables the viticulturist to manipulate grape berry aroma and consequently the composition of wine.