Vitamin A is a group of fat-soluble compounds that humans cannot synthesize themselves, so they must be widely present in the human diet. If there is a deficiency of the vitamin, it can lead to many problems, including blindness, which, in addition to hunger, is a big problem in most developing countries where the starchy diet of the population does not contain sufficient amounts of said vitamin. For this purpose, scientists have developed several cultivated crops that have increased synthesis and accumulation of provitamin A, which is converted into functional vitamin A in the human body. This was achieved by biofortification methods (conventional crossing and genetic engineering of cultivated crops) and by means of 2 approaches: overexpression and gene silencing. The methods used led to a significant accumulation of carotenoids in the edible parts of rice, tomatoes, potatoes and corn, and to an obvious change in the colour of their fruits, which, with a higher content of carotenoids, showed more intense shades of orange or yellow colour. For the successful manipulation of carotenogenesis, a thorough understanding of the biosynthesis pathway of carotenoids is crucial and played a key role in the selection of individual genes. In the cultivated plants described, the genes were mainly of bacterial origin (genus Erwinia), but plant genes were also used, both endogenous and genes from other plant species, which by themselves contain larger amounts of carotenoids.
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