Abstract
Glycosylated volatile precursors are important, particularly in wine grape berries, as they contribute to the final aroma in wines by releasing volatile aglycones during yeast fermentation and wine storage. Previous study demonstrated that VviGT14 was functioned as a critical monoterpene glucosyltransferase in grape berry, while the transcriptional regulation mechanism of VviGT14 was still unknown. Here we identified VviWRKY40 as a binding factor of VviGT14 promoter by both DNA pull-down and yeast one-hybrid screening, followed by a series of in vitro verification. VviWRKY40 expression pattern negatively correlated with that of VviGT14 in grape berries. And the suppressor role of VviWRKY40 was further confirmed by using the dual luciferase assay with Arabidopsis protoplast and grape cell suspension system. Furthermore, the grape suspension cell ABA treatment study showed that ABA downregulated VviWRKY40 transcript level but promoted that of VviGT14, indicating that VviWRKY40 was at the downstream of ABA signal transduction network to regulate monoterpenoid glycosylation. These data extend our knowledge of transcriptional regulation of VviGT14, and provide new targets for grape breeding to alter monoterpenoid composition.
Highlights
Aroma is one of the important indicators of grape and wine quality, which directly affects consumers’ acceptance
The VviGT14 promoter contained several cis-acting elements related to the adversity stress and hormone responses, such as an ABA response element (ABRE) at −578 bp, CGTCA-motif at −173 bp, and GARE-motif at −668 bp, which respond to methyl jasmonate and gibberellin, respectively
The results showed that ABA application led to more than two-fold increase in VviGT14 expression and a visible reduction in VviWRKY40 expression, whereas the expression of VviNCED1, which is required for ABA biosynthesis, was greatly promoted (Figure 9B)
Summary
Aroma is one of the important indicators of grape and wine quality, which directly affects consumers’ acceptance. There are mainly six groups of aroma compounds in Vitis vinifera L. wine grapes, namely, terpenoids, norisoprenoids, aromatic compounds, aliphatic volatile compounds, methoxypyrazines, and organo-sulfur compounds. Among these compounds, grape-derived terpenoids have garnered interest because they have a low sensory threshold values and impart pleasant floral/fruity odor. Monoterpenoids are typical volatile compounds of white wines made from aromatic Muscat grape varieties, in which their concentration may exceed the threshold by 100-fold [1].
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