Genetic and physiological bases of healthy attributes of grapes and wine

Grapes and wine are claimed to have beneficial effects on human health, due mainly to their high polyphenolic content. Polyphenols include several classes of compounds regarded mostly as effective antioxidants in humans when assumed in the diet (e.g., hydroxycinnamic acids, flavonols, anthocyanins, tannins (proanthocyanidins) and stilbenes). The latter deserve particular attention due to their crucial function in plants; stilbene phytoalexins accumulate in the soft tissues of the vine and they are produced by the phenylpropanoid pathway. Stilbene synthase (STS) is the key enzyme of the above pathway, and it produces resveratrol, the basic monomer which can be glycosylated, hydroxylated, methylated or converted into more complex compounds (dimers, trimers, tetramers). According to the grapevine genome sequence, STS is encoded by a gene family of many highly similar paralogues, and recent data account for their expression in different grapevine organs. At the berry (fruit) level, stilbenes are produced by the skin after the occurrence of a biotic or abiotic stress, and by the seeds as constitutive compounds. Berry skin is the main available source of stilbenes from grape and wine consumption. Thus it is crucial to deeply understand mechanisms of biotic and abiotic elicitors of stilbene phytoalexins in order to increase their production. Study of metabolomics allows identification of a large array of stilbenes in grapes and wine that could have major implications for health. Under the same elicitation pressure, the final concentration of stilbenes in grapes and wine is affected by decisions applied for viticultural practices and, in the case of wine, for winemaking (i.e., oenological factors). The most recent health claims for resveratrol are discussed, including the effect in extending the lifespan of organisms (human beings, too) by triggering the Sir/SIRT genes.