Mesocarp localization of a bi-functional resveratrol/hydroxycinnamic acid glucosyltransferase of Concord grape (Vitis labrusca)

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Resveratrol is a stilbene with well-known health-promoting effects in humans that is produced constitutively or accumulates as a phytoalexin in several plant species including grape (Vitissp.). Grape berries accumulate stilbenes in the exocarp ascis- andtrans-isomers of resveratrol, together with their respective 3-O-monoglucosides. An enzyme glucosylatingcis- andtrans-resveratrol was purified to apparent homogeneity from Concord (Vitis labrusca) grape berries, and peptide sequencing associated it to an uncharacterizedVitis viniferafull-length clone (TC38971, tigr database). A corresponding gene fromVitis labrusca(VLRSgt) had 98% sequence identity to clone TC38971 and 92% sequence identity to aVitis vinifera p-hydroxybenzoic acid glucosyltransferase that produces glucose esters. The recombinant enzyme was active over a broad pH range (5.5–10), producing glucosides of stilbenes, flavonoids and coumarins at higher pH and glucose esters of several hydroxybenzoic and hydroxycinnamic acids at low pH.Vitis labruscagrape berries accumulated both stilbene glucosides and hydroxycinnamic acid glucose esters, consistent with the bi-functional role of VLRSgt in stilbene and hydroxycinnamic acid modification. While phylogenetic analysis of VLRSgt and other functionally characterized glucosyltransferases places it with other glucose ester-producing enzymes, the present results indicate broader biochemical activities for this class of enzymes.

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