Provitamin A biofortification of crop plants: a gold rush with many miners

Carotenoids are synthesized de novo by plants, where they play fundamental physiological roles as photosynthetic pigments and precursors for signaling molecules. They are also essential components of a healthy diet, as dietary antioxidants and vitamin A precursors. Vitamin A deficiency is a public health problem in developing countries, which has prompted a series of efforts toward the biofortification of plant-derived foods with provitamin A carotenoids (mainly β-carotene), giving rise to 'golden' crops. Since the 'golden rice' exploit, a number of biofortified crops have been generated, using transgenic approaches as well as conventional breeding. Bioavailability studies have demonstrated the efficacy of several 'golden' crops in maintaining vitamin A status. This review presents the state of the art and the areas that need further experimentation.