Search

Flavonoids are secondary metabolites with multiple functions. In grape ( Vitis vinifera), the most abundant flavonoids are proanthocyanidins ( PAs), major quality determinants for fruit and wine. However, knowledge about the regulation of PA composition is sparse. Thus, we aimed to identify novel genomic regions involved in this mechanism., Expression quantitative trait locus (e QTL) mapping was performed on the transcript abundance of five downstream PA synthesis genes (dihydroflavonol reductase ( Vv DFR), leucoanthocyanidin dioxygenase ( Vv LDOX), leucoanthocyanidin reductase ( Vv LAR1), Vv LAR2 and anthocyanidin reductase ( Vv ANR)) measured by real-time quantitative PCR on a pseudo F1 population in two growing seasons., Twenty-one e QTLs were identified; 17 of them did not overlap with known candidate transcription factors or cis-regulatory sequences. These novel loci and the presence of digenic epistasis support the previous hypothesis of a polygenic regulatory mechanism for PA biosynthesis., In a genomic region co-locating e QTLs for Vv DFR, Vv LDOX and Vv LAR1, gene annotation and a transcriptomic survey suggested that Vv MYBC2- L1, a gene coding for an R2 R3- MYB protein, is involved in regulating PA synthesis. Phylogenetic analysis showed its high similarity to characterized negative MYB factors. Its spatiotemporal expression profile in grape coincided with PA synthesis. Its functional characterization via overexpression in grapevine hairy roots demonstrated its ability to reduce the amount of PA and to down-regulate expression of PA genes. [ABSTRACT FROM AUTHOR]

In grapevine ( Vitis vinifera), anthocyanins are responsible for most of the red, blue, and purple pigmentation found in the skin of berries. In cells, anthocyanins are synthesized in the cytoplasm and accumulated into the vacuole. However, little is known about the transport of these compounds through the tonoplast. Recently, the sequencing of the grapevine genome allowed us to identify genes encoding proteins with high sequence similarity to the Multidrug And Toxic Extrusion (MATE) family. Among them, we selected two genes as anthocyanin transporter candidates and named them anthoMATF21 (AM1) and AM3. The expression of both genes was mainly fruit specific and concomitant with the accumulation of anthocyanin pigment. Subcellular localization assays in grapevine hairy roots stably transformed with AM1:: or AM3::green fluorescent protein fusion protein revealed that AM1 and AM3 are primarily localized to the tonoplast. Yeast vesicles expressing anthoMATEs transported acylated anthocyanrns in the presence of MgATP. Inhibitor studies demonstrated that AM1 and AM3 proteins act in vitro as vacuolar H+-dependent acylated anthocyanin transporters. By contrast, under our experimental conditions, anthoMATEs could not transport malvidin 3-O-glucoside or cyanidin 3-O-glucoside, suggesting that the acyl conjugation was essential for the uptake. Taken together, these results provide evidence that in vitro the two grapevine AM1 and AM3 proteins mediate specifically acylated anthocyanin transport. [ABSTRACT FROM AUTHOR]

Grapevine (Vitis) is considered to be one of the major fruit crops in the world based on hectares cultivated and economic value. Grapes are used not only for wine but also for fresh fruit, dried fruit, and juice production. Wine is by far the major product of grapes, and the focus of this chapter is on wine grape cultivars. Grapevine cultivars of Vitis vinifera L. have a reputation for producing premium quality wines. These premium quality wines are produced from a small number of cultivars that enjoy a high level of consumer acceptance and are firmly entrenched in the market place because of varietal name branding and the association of certain wine styles and regions with specific cultivars. In light of this situation, grapevine improvement by a transgenic approach is attractive when compared to a classical breeding approach. The transfer of individual traits as single genes with a minimum disruption to the original genome would leave the traditional characteristics of the cultivar intact. However, a reliable transformation system is required for a successful transgenic approach to grapevine improvement. There are three criteria for achieving an efficient Agrobacterium-mediated transformation system: (1) the production of highly regenerative transformable tissue, (2) optimal cocultivation conditions for both grapevine tissue and Agrobacterium, and (3) an efficient selection regime for transgenic plant regeneration. In this chapter, we describe a grapevine transformation system that meets these criteria. We also describe a protocol for the production of transformed roots suitable for functional gene studies and for the production of semi-transgenic grafted plants.