Biotechnological production of resveratrol in tomato improves the health properties of fruits and affects the seeds set

Resveratrol, a plant phenolic compound, is found in grapes and red wine but is not widely distributed in other common food sources. The pathway for resveratrol biosynthesis is well characterised. In this work metabolic engineering of resveratrol has been achieved in tomato plants (Lycopersicon esculentum Mill.). Tomato plants synthesising resveratrol were obtained via the heterologous expression of a grape (Vitis vinifera L.) cDNA encoding for the enzyme stilbene synthase (StSy), under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Transgenic plants accumulated novel compounds identified by high-pressure liquid chromatography, as trans-resveratrol and trans-resveratrol-glucopyranoside. The amount of trans-resveratrol and its piceid form was evaluated in different tissues of the transgenic plants. It was found that the content of the metabolite varied during fruit maturation by up to 53 ?g g-1 fresh weight of the total trans-resveratrol at the red stage of ripening. This metabolite accumulation was possibly dependent upon a combination of sufficiently high levels of stilbene synthase and the availability of substrates. To establish whether the presence of a novel antioxidant molecule affected the redox regulation in transgenic tomato fruit cells, the effect of resveratrol accumulation on the naturally present antioxidant pool was analysed. We show here that in transgenic fruits which accumulate trans-resveratrol there is an increase in the levels of ascorbate and glutathione, the soluble antioxidants of primary metabolism, as well as in the total antioxidant activity. These results could explain the higher capability of transgenic fruits to counteract the pro-inflammatory effects of phorbol ester in monocyte-macrophages, via the inhibition of induced cyclooxygenase-2 enzyme. Moreover stsy overexpression caused altered pollen formation and male sterility, probably due to competition between the introduced StSy enzyme and the endogenous Chalcone Synthase for the common substrates. Thus, StSy gene expression in tomato can be promising strategy for the production of parthenocarpic fruits and the development of a novel hybrid seed system.