Carotenoid Biosynthesis and their Regulation in Citrus Fruits

Carotenoids are the main pigments responsible for the attractive color of the peel and pulp of citrus fruits and greatly contribute to their nutritional and antioxidant value. Fruits of different Citrus species display a broad array of color singularities and in many cultivars the peel and the pulp also exhibit different color, envisaging specieand tissuespecific regulation of the carotenoid content and composition. In addition, citrus mutants affected in fruit color are a useful experimental system to identify molecular mechanisms regulating carotenoid biosynthesis. Citrus is, therefore, an excellent model to study fruit carotenoid accumulation and their regulation. In this review, we summarize and update information on carotenoid content and composition in fruits of agronomically important Citrus species. Current understanding of carotenoids biosynthesis in citrus, highlighting the main regulatory steps of the pathway and how may be related to carotenoid content and complement in peel and pulp of Citrus fruits are discussed. Finally, the effect of environmental and endogenous factors on citrus fruits carotenoids is also evaluated. _____________________________________________________________________________________________________________