Grapevine flavan 3-ols are found as monomers, oligomers, and polymers. In vegetative organs, PA content constantly increases during leaf development, but the rate of synthesis decreases in old leaves ( Bogs et al., 2005).
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induction of ripening Kennedy et al., 2001 Verriès et al., 2008), whereas anthocyanin accumulation in skin is restricted to ripening. In pericarp, flavan 3-ols accumulate mainly before véraison (i.e. In grapevine fruit, flavan 3-ols are present in skin and seed tissues ( Kennedy et al., 2001) and to a lesser extent in the pulp ( Mané et al., 2007 Verriès et al., 2008). Grapevine ( Vitis vinifera) flavonoids are also of particular importance for wine quality: anthocyanins of red-skinned cultivars are responsible for the red wine color, while PAs or so-called “condensed tannins” confer its astringency to the wine. flavan 3-ol oligomers and polymers) protect plants against microbial attacks and fungal growth ( Dixon et al., 2005), and anthocyanins of flowers and fruits attract pollinators and help to disseminate seeds ( Grotewold, 2006). In particular, flavonols play a role in protection against UV radiation ( Winkel-Shirley, 2002), proanthocyanidins (PAs i.e. anthocyanins, flavonols, and flavan 3-ols) and accumulate in a wide variety of plant tissues, where they are involved in diverse functions. The functional annotation of the genes whose expression was modified revealed putative new actors of the proanthocyanidin pathway, such as glucosyltransferases and transporters.įlavonoids are a family of plant secondary metabolites that comprise several groups of compounds (e.g. Both genes significantly activated enzymes of the flavonoid pathway, including anthocyanidin reductase and leucoanthocyanidin reductase 1, the specific terminal steps in the biosynthesis of epicatechin and catechin, respectively, but not leucoanthocyanidin reductase 2. High-throughput transcriptomic analyses of transformed grapevine organs identified a large set of putative targets of the VvMybPA1 and VvMybPA2 transcription factors. Ectopic expression of either VvMybPA1 or VvMybPA2 in grapevine hairy roots induced qualitative and quantitative changes of the proanthocyanidin profiles. This transcription factor shows very high protein sequence homology with other plant Myb factors, which regulate flavonoid biosynthesis.
A novel Myb factor, VvMybPA2, which is described in this study, is in contrast mainly expressed in the exocarp of young berries and in the leaves. A previous study has already identified VvMybPA1 as the first transcription factor involved in the regulation of the proanthocyanidin pathway during seed development in grapevine. In grapevine berry, these compounds are mainly accumulated in exocarps and seeds in the very early stages of development. Grapevine ( Vitis vinifera) proanthocyanidins contribute to plant defense mechanisms against biotic stress and also play a critical role in organoleptic properties of wine.
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