ABSTRACT
(-)-Rotundone is a potent odorant molecule with a characteristic spicy aroma existing in various plants including grapevines (Vitis vinifera). It is considered to be a significant compound in wines and grapes because of its low sensory threshold and aroma properties. (-)-Rotundone was first identified in red wine made from the grape cultivar Syrah and here we report the identification of VvSTO2 as a α-guaiene 2-oxidase which can transform α-guaiene to (-)-rotundone in the grape cultivar Syrah. It is a cytochrome P450 (CYP) enzyme belonging to the CYP 71BE subfamily, which overlaps with the very large CYP71D family and, to the best of our knowledge, this is the first functional characterization of an enzyme from this family. VvSTO2 was expressed at a higher level in the Syrah grape exocarp (skin) in accord with the localization of (-)-rotundone accumulation in grape berries. α-Guaiene was also detected in the Syrah grape exocarp at an extremely high concentration. These findings suggest that (-)-rotundone accumulation is regulated by the VvSTO2 expression along with the availability of α-guaiene as a precursor. VvSTO2 expression during grape maturation was considerably higher in Syrah grape exocarp compared to Merlot grape exocarp, consistent with the patterns of α-guaiene and (-)-rotundone accumulation. On the basis of these findings, we propose that VvSTO2 may be a key enzyme in the biosynthesis of (-)-rotundone in grapevines by acting as a α-guaiene 2-oxidase.
Subject(s)
Biocatalysis , Cytochrome P-450 Enzyme System/metabolism , Odorants , Sesquiterpenes/metabolism , Vitis/enzymology , Amino Acid Sequence , Azulenes/metabolism , Cytochrome P-450 Enzyme System/chemistry , Cytochrome P-450 Enzyme System/genetics , Enzyme Assays , Fruit/enzymology , Fruit/genetics , Gas Chromatography-Mass Spectrometry , Gene Expression Regulation, Plant , Genes, Plant , Kinetics , Molecular Sequence Data , Phylogeny , Plant Proteins/chemistry , Plant Proteins/genetics , Plant Proteins/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Recombination, Genetic/genetics , Sequence Alignment , Sesquiterpenes, Guaiane/metabolism , Substrate Specificity , Vitis/geneticsABSTRACT
Linalool is an important compound that contributes to the floral aroma in wines. This study showed the effect of light exposure on linalool accumulation in berries. The grape bunches were covered with films that block the full light spectrum (Shade) and the UV spectrum (UV-block), and a transparent film (Control). The linalool content was significantly higher in juice from Control-covered berries than in juice from Shade- and UV-block-covered berries, and the expression levels of the representative genes in linalool biosynthesis in Shade- and UV-block-covered berries were markedly lower than in Control-covered berries. These findings suggest that exposing berries to light is essential for linalool biosynthesis. To reflect sunlight onto grape clusters, reflective sheets were placed on the ground of a vineyard. The linalool content in berries exposed to sunlight reflected from the reflective sheets was higher than those in the control.
Subject(s)
Fruit/metabolism , Fruit/radiation effects , Light , Monoterpenes/metabolism , Vitis/metabolism , Vitis/radiation effects , Acyclic Monoterpenes , Fruit/genetics , Gene Expression Regulation, Plant/radiation effects , Organ Specificity , Surface Properties , Vitis/geneticsABSTRACT
2,5-Dimethyl-4-hydroxy-3(2H)-furanone (furaneol) is an important aroma compound in fruits, such as pineapple and strawberry, and is reported to contribute to the strawberry-like note in some wines. Several grapevine species are used in winemaking, and furaneol is one of the characteristic aroma compounds in wines made from American grape (Vitis labrusca) and its hybrid grape. Furaneol glucoside was recently isolated as an important furaneol derivative from the hybrid grapevine cultivar, Muscat Bailey A (V. labrusca × V. vinifera), and this was followed by its isolation from some fruits such as strawberry and tomato. Furaneol glucoside is a significant 'aroma precursor of wine' because furaneol is liberated from it during alcoholic fermentation. In this study, a glucosyltransferase gene from Muscat Bailey A (UGT85K14), which is responsible for the glucosylation of furaneol was identified. UGT85K14 was expressed in the representative grape cultivars regardless of species, indicating that furaneol glucoside content is regulated by the biosynthesis of furaneol. On the other hand, furaneol glucoside content in Muscat Bailey A berry during maturation might be controlled by the expression of UGT85K14 along with the biosynthesis of furaneol. Recombinant UGT85K14 expressed in Escherichia coli is able to transfer a glucose moiety from UDP-glucose to the hydroxy group of furaneol, indicating that this gene might be UDP-glucose: furaneol glucosyltransferase in Muscat Bailey A.
Subject(s)
Glucosyltransferases/genetics , Plant Proteins/genetics , Vitis/genetics , Cloning, Molecular , Escherichia coli/genetics , Furans/metabolism , Glucosyltransferases/metabolism , Molecular Sequence Data , Organisms, Genetically Modified , Phylogeny , Plant Proteins/metabolism , Recombinant Proteins , Sequence Analysis, DNA , Uridine Diphosphate Glucose/metabolism , Vitis/metabolismABSTRACT
The biosynthesis of S-(3-hexan-1-ol)-glutathione (3MH-S-glut) and S-(3-hexan-l-ol)-L-cysteine (3MH-S-cys), which act as flavour precursors in wines, in Vitis vinifera grapes exposed to various environmental stress conditions is reported here. Ultraviolet (UV-C) irradiation, water deficit, and biological stimulation up-regulated 3MH-S-glut and 3MH-S-cys biosynthesis in grape leaves. 3MH-S-glut and 3MH-S-cys contents in grape berries were increased by cold shock, heat shock, UV-C irradiation, and biological stimulation. The results suggest that environmental stress enhances the biosynthesis of both flavour precursors in grapevine. The transcription of VvGST1, VvGST3, VvGST4, and GGT in grapevine exposed to the stress conditions was increased markedly compared with that in control grapevine. Also, UV irradiation increased GST (glutathione S-transferase) and GGT (γ-glutamyl transferase) enzyme activities in grape berries. Recombinant VvGST3 and VvGST4, but not VvGST1, mediated the synthesis of 3MH-S-glut from reduced glutathione and trans-2-hexenal in vitro. The enzymatic mediation of flavour precursor production is a novel function of plant GSTs and may result in the detoxification of damaged grape cells under stress conditions.
Subject(s)
Cysteine/analogs & derivatives , Flavoring Agents/metabolism , Glutathione Transferase/metabolism , Glutathione/analogs & derivatives , Plant Proteins/metabolism , Vitis/enzymology , Vitis/physiology , Cold Temperature , Cysteine/biosynthesis , Droughts , Enzyme Activation , Gene Expression Regulation, Enzymologic , Glutathione/biosynthesis , Glutathione Transferase/genetics , Hot Temperature , Plant Proteins/genetics , Stress, Physiological , Ultraviolet Rays , Vitis/genetics , Vitis/radiation effects , Wine/analysisABSTRACT
3-Sulfanylhexan-1-ol (3SH) is an important contributor to the fruity notes of wine. 3SH exists as odorless precursors in grape and its release from the precursors is generally mediated by yeast during alcoholic fermentation. Here, the impact of lactic acid bacteria on 3SH production was investigated. Among the species tested, only Lactobacillus plantarum released 3SH from S-3-(hexan-1-ol)-l-cysteine (3SH-S-cys) and S-3-(hexan-1-ol)-l-cysteinylglycine (3SH-S-cysgly) in the whole-cell biotransformation assay. The conversion yields of 3SH from 3SH-S-cysgly by L. plantarum were always higher than those from 3SH-S-cys, suggesting that the direct cleavage of 3SH-S-cysgly to yield 3SH predominantly occurred. L. plantarum biotransformed the 3SH precursors, including 3SH-S-glut, to release 3SH in fermented grape juice. The results indicate that L. plantarum induces the release of 3SH from the 3SH precursors. To the best of our knowledge, this is the first study showing the impact of L. plantarum on thiol precursor biotransformation.