, and UDP glucose-flavonoid 3-o-glucosyl transferase [UFCT]) was determined. I n flowers and grape berry skins, expression of all of the genes, except UFCT, was detected up to 4 weeks postflowering, followed by a reduction in this expression 6 to 8 weeks postflowering. Expression of CHS, CHI, F3H, DFR, LDOX, and UFCT then increased 1 O weeks postflowering, coinciding with the onset of anthocyanin synthesis. I n grape berry flesh, no PAL or UFCT expression was detected at any stage of development, but CHS, CHI, F3H, DFR, and LDOX were expressed up to 4 weeks postflowering. These results indicate that the onset of anthocyanin synthesis in ripening grape berry skins coincides with a coordinated increase in expression of a number of genes in the anthocyanin biosynthetic pathway, suggesting the involvement of regulatory genes. UFCT is regulated independently of the other genes, suggesting that in grapes the major control point in this pathway is later than that observed in maize, petunia, and snapdragon.

No abstract

The transition from vegetative to reproductive growth is an essential process in the life cycle of plants. Plant floral induction pathways respond to both environmental and endogenous cues and much has been learnt about these genetic pathways by studying mutants of Arabidopsis. Gibberellins (GAs) are plant growth regulators important in many aspects of plant growth and in Arabidopsis they promote flowering. Here we provide genetic evidence that GAs inhibit flowering in grapevine. A grapevine dwarf mutant derived from the L1 cell layer of the champagne cultivar Pinot Meunier produces inflorescences along the length of the shoot where tendrils are normally formed. The mutated gene associated with the phenotype is a homologue of the wheat 'green revolution' gene Reduced height-1 (ref. 6) and the Arabidopsis gene GA insensitive (GAI). The conversion of tendrils to inflorescences in the mutant demonstrates that the grapevine tendril is a modified inflorescence inhibited from completing floral development by GAs.

Abstract:Wine is an ancient beverage and has been prized throughout time for its unique and pleasing flavor. Wine flavor arises from a mixture of hundreds of chemical components interacting with our sense organs, producing a neural response that is processed in the brain and resulting in a psychophysical percept that we readily describe as "wine." The chemical components of wine are derived from multiple sources; during fermentation grape flavor components are extracted into the wine and new compounds are formed by numerous chemical and biochemical processes. In this review we discuss the various classes of chemical compounds in grapes and wines and the chemical and biochemical processes that influence their formation and concentrations. The overall aim is to highlight the current state of knowledge in the area of grape and wine aroma chemistry.

The expression of seven genes from the anthocyanin biosynthesis pathway was determined in different tissues of Shiraz grapevines. All of the tissues contained proanthocyanidins, but only the berry skin accumulated anthocyanins. In most tissues, all of the flavonoid genes except UDP glucose-flavonoid 3-o-glucosyl transferase (UFGT) were expressed, but UFGT expression was only detected in berry skin. Similar patterns of expression were observed in the skin of other red grapes. In white grapes, UFGT expression was not detected. White grape cultivars appear to lack anthocyanins because they lack UFGT, although they also had decreased expression of other flavonoid pathway genes.

Plant stilbenes are phytoalexins that accumulate in a small number of plant species, including grapevine (Vitis vinifera), in response to biotic and abiotic stresses and have been implicated in many beneficial effects on human health. In particular, resveratrol, the basic unit of all other complex stilbenes, has received widespread attention because of its cardio-protective, anticarcinogenic, and antioxidant properties. Although stilbene synthases (STSs), the key enzymes responsible for resveratrol biosynthesis, have been isolated and characterized from several plant species, the transcriptional regulation underlying stilbene biosynthesis is unknown. Here, we report the identification and functional characterization of two R2R3-MYB-type transcription factors (TFs) from grapevine, which regulate the stilbene biosynthetic pathway. These TFs, designated MYB14 and MYB15, strongly coexpress with STS genes, both in leaf tissues under biotic and abiotic stress and in the skin and seed of healthy developing berries during maturation. In transient gene reporter assays, MYB14 and MYB15 were demonstrated to specifically activate the promoters of STS genes, and the ectopic expression of MYB15 in grapevine hairy roots resulted in increased STS expression and in the accumulation of glycosylated stilbenes in planta. These results demonstrate the involvement of MYB14 and MYB15 in the transcriptional regulation of stilbene biosynthesis in grapevine.

The evolution of volatile compounds was explored in grape berries at fortnightly intervals from fruit-set to late ripening to identify when biosynthetic pathways may be targeted for enhancement of grape and wine aroma. Stepwise linear discriminant analysis (SLDA) fully recognized patterns in berry physiological developmental stages with most of the variance (>99.0%) explained. The preveraison berry developmental stage was identified as a transition stage for volatile compound biosynthesis when most compounds were potentially sequestered to nonvolatile conjugates and berries lost their potential to synthesize esters and terpenes. Terpenes (predominantly eucalyptol, beta-caryophyllene, and alpha-humulene) characterized early berry development, whereas benzene derivatives (2-phenylethanol and 2-phenylethanal) appeared toward late ripening. Furthermore, C(6) volatile compounds changed from acetate esters to aldehydes and finally to alcohols during early, middle, and late berry developmental stages, respectively. The dominance of alcohols in the late stages of berry development, preceded by aldehydes, offers an opportunity for alcohols to aldehydes ratios to be used in the prediction of harvest timing for enhanced grape and wine aroma. The evolution of volatile compounds during berry development suggests a greater dependency on enzyme activity and specificity than extent of fatty acid unsaturation. The dependence of the stage of berry development on the accumulation of the products of alcohol dehydrogenase (ADH), alcohol acetyl transferase (AAT), and enal isomerase enzyme activity from the lipoxygenase pathway raises possibilities for the manipulation of aroma profiles in grapes and wines.

We report here the cloning and optimized expression at 16°C and the characterization of a Vitis vinifera UDPglucose:flavonoid 3-O-glucosyltransferase, an enzyme responsible for a late step in grapevine anthocyanin biosynthesis. The properties of this and other UDP-glucose:flavonoid 3-O-glucosyltransferases, homologues of the product encoded by the maize Bronze-1 locus, are a matter of conjecture. The availability of a purified recombinant enzyme allowed for the unambiguous determination of the characteristics of a flavonoid 3-O-glucosyltransferase. Kinetic analyses showed that k cat for glucosylation of cyanidin, an anthocyanidin substrate, is 48 times higher than for glucosylation of the flavonol quercetin, whereas K m values are similar for both substrates. Activity toward other classes of substrates is absent. Cu 2؉ ions strongly inhibit the action of this and other glucosyltransferases; however, we suggest that this phenomenon in large part is due to Cu 2؉ -mediated substrate degradation rather than inhibition of the enzyme. Additional lines of complementary biochemical data also indicated that in the case of V. vinifera, the principal, if not only, role of UDP-glucose:flavonoid 3-Oglucosyltransferases is to glucosylate anthocyanidins in red fruit during ripening. Other glucosyltransferases with a much higher relative activity toward quercetin are suggested to glucosylate flavonols in a distinct spatial and temporal pattern. It should be considered whether gene products homologous to Bronze-1 in some cases more accurately should be referred to as UDPglucose:anthocyanidin 3-O-glucosyltransferases.Phytochemists have identified some 70,000 plant chemicals, many thousands of which are glycosylated (1). From a chemical point of view, two main properties differ between the glycosylated secondary products and their respective aglycones, as glycosylation invariably results in enhanced water solubility and lower chemical reactivity. Glycosylated compounds are therefore often thought of as transportable storage compounds or indeed waste/detoxification products assumed to lack physiological activity (2).Despite the widespread occurrence of glycosylated secondary metabolites, including flavonols (3), anthocyanins (4), monoterpenes (5), plant hormones (2), and metabolites of systemic fungicides (6), isolation and characterization of purified enzymes responsible for their metabolism have only been reported in a couple of select instances (7,8). The most widely studied groups of plant glycosyltransferases are those associated with the biosynthesis of flavonoid glucosides, including flavonol glucosides, flavanone glucosides, and anthocyanins (3, 4, 9, 10). Earliest reports included the detection of an anthocyanidin and flavonol glucosylating activity in endosperm extracts of maize (Zea mays), (11)(12)(13). This work formed the basis for identification by transposon tagging of the gene product of the maize Bronze-1 locus (14). cDNAs encoding flavonoid glucosyltransferases have been isolated from a number of plant species uti...