| Sumario: | Orange is a major crop and an important source of health-promoting bioactive compounds. Increasing the levels of specific antioxidants in orange fruit through metabolic engineering could strengthen the fruit's health benefits. In this work, we have afforded enhancing the -carotene content of orange fruit through blocking by RNA interference the expression of an endogenous -carotene hydroxylase gene (Cs-CHX) that is involved in the conversion of -carotene into xanthophylls. Additionally, we have simultaneously overexpressed a key regulator gene of flowering transition, the FLOWERING LOCUS T from sweet orange (CsFT), in the transgenic juvenile plants, which allowed us to obtain fruit in an extremely short period of time. Silencing the Cs-CHX gene resulted in oranges with a deep yellow (golden') phenotype and significant increases (up to 36-fold) in -carotene content in the pulp. The capacity of -carotene-enriched oranges for protection against oxidative stress in vivo was assessed using Caenorhabditis elegans as experimental animal model. Golden oranges induced a 20% higher antioxidant effect than the isogenic control. This is the first example of the successful metabolic engineering of the -carotene content (or the content of any other phytonutrient) in oranges and demonstrates the potential of genetic engineering for the nutritional enhancement of fruit tree crops.
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