Flavonoids pathway engineering for the induction of novel sets of healthy phytochemicals in tomato fruit.

Flavonoids are a large family of plant polyphenolic secondary metabolites. Although they are widespread throughout the plant kingdom, some flavonoid classes are specific for only a few plant species. Due to their presumed health benefits there is growing interest in the development of food crops with tailor-made levels and composition of flavonoids, designed to exert an optimal biological effect. In order to explore the possibilities of flavonoid engineering in tomato fruits, we have targeted this pathway towards novel classes of potentially healthy flavonoids. Using a structural flavonoid gene (encoding a grape stilbene synthase), we were able to produce transgenic tomatoes accumulating new stilbene-related phytochemicals. Afterwards, we performed a breeding programme taking advantage of the ability of some transcription factors (MYB12, Delila and Rosea) to strongly activate the expression of several phenylpropanoid biosynthetic genes and provide high rates of metabolic flux for different classes of polyphenols. Biochemical analyses showed that these new tomato lines were able to accumulate high levels of specific classes of polyphenols such as stilbenes, flavonols and anthocyanins. We demonstrated that, due to the presence of the novel phytochemicals, the transgenic tomato fruits displayed a significantly higher antioxidant profile. Our data show that a combination of biosynthetic and regulatory genes together with the availability of natural tomato varieties could provide novel insights into genetic and biochemical regulation of the flavonoid pathway in this worldwide important vegetable.