Rubi-colored crops with built-in ketocarotenoid biosynthetic pathway

Ketocarotenoid–biofortified crops are required as natural additives with respect to their Rubi-like reddish color and strong antioxidative properties for foods and feeds. They can be an alternative means of microalgal and bacterial systems and do not depend on chemical synthesis, providing safe, sustainable, and processing-free platforms. To reach sufficient commercial demands, different metabolic engineering strategies have been used in diverse crop plants. In this study, we summarized the current achievements for de novo production of ketocarotenoids in major crops and described host crop-specific tactics to optimize the ketocarotenoid biosynthetic pathway, considering the following different levels and types of carotenoid being accumulated as precursors: lutein and zeaxanthin in maize seeds; lutein in rice seeds, canola seeds, soybean seeds, and tobacco flowers; zeaxanthin in potato tubers; β–carotene in carrot roots; and lycopene in tomato fruits. This study suggests prospects for the advanced performance of ketocarotenoid biofortification in crops in two crucial points: host crop cultivar and the elaborately designed genetic strategies. The latter includes an increase in the total carotenoid capacity by co-consideration to supply precursors and stabilizers, the prevention of metabolite loss in competing or catabolic pathways or both pathways, and the sensible choice of genes and genetic elements for optimal expression. Furthermore, progresses in synthetic biology and new biotechnology, such as genome editing, could accelerate the development of high-valued “Rubi Crops,” which satisfy the nutritional and functional needs of humans and animals.