Deep inside the genetic regulation of ascorbic acid during fruit ripening and postharvest storage

Since the early characterization of vitamin C (ascorbic acid, AsA) as a major antioxidant molecule that human beings are unable to synthesize de novo, the discovery of adequate natural sources of AsA, as well as its elevation and preservation in fruit and vegetables through the entire food chain, has become a cutting-edge research topic in plant science as well as in nutrition research. Over the last decades, the progressive genetic characterization of the AsA metabolic pathways, including biosynthesis, recycling and degradation, in combination with the availability of a plethora of advanced molecular and biotechnological techniques, created high expectations towards the enhancement of AsA in horticultural crops. Yet, either the single or the multiple overexpression of AsA biosynthetic and recycling genes failed to boost AsA contents beyond a certain level, confirming the difficulties in “un-locking” AsA biosynthesis, probably owing to the tight regulation of the biosynthetic machinery. From an evolutionary point of view, the unlimited rise in AsA content in horticultural crops may be infeasible, as AsA itself may negatively interfere with plant development, acting as prooxidant depending on the conditions. In the present review, we aimed to discuss the recent genetic advances in improving AsA content of horticultural crops, as well as the potential of maintaining the reduced AsA pool during postharvest.