Abstract
Carotenoids play a critical role in animal and human health. Animals and humans are unable to synthesize carotenoids de novo, and therefore rely upon diet as sources of these compounds. However, major staple cereals often contain only small amounts of carotenoids in their grains. Consequently, there is considerable interest in genetic manipulation of carotenoid content in cereal grain. In this review, we focus on carotenoid metabolism and regulation in non-green plant tissues, as well as genetic manipulation in staple cereals such as rice, maize, and wheat. Significant progress has been made in three aspects: (1) seven carotenogenes play vital roles in carotenoid regulation in non-green plant tissues, including 1-deoxyxylulose-5-phosphate synthase influencing isoprenoid precursor supply, phytoene synthase, β-cyclase, and ε-cyclase controlling biosynthesis, 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase and carotenoid cleavage dioxygenases responsible for degradation, and orange gene conditioning sequestration sink; (2) provitamin A-biofortified crops, such as rice and maize, were developed by either metabolic engineering or marker-assisted breeding; (3) quantitative trait loci for carotenoid content on chromosomes 3B, 7A, and 7B were consistently identified, eight carotenogenes including 23 loci were detected, and 10 gene-specific markers for carotenoid accumulation were developed and applied in wheat improvement. A comprehensive and deeper understanding of the regulatory mechanisms of carotenoid metabolism in crops will be beneficial in improving our precision in improving carotenoid contents. Genomic selection and gene editing are emerging as transformative technologies for provitamin A biofortification.
Highlights
Carotenoids are mainly C40 isoprenoids comprising a large family with more than 700 members that are widely distributed in plants, algae, fungi, and bacteria (Khoo et al, 2011)
For better genetic manipulation of carotenoid content within cereal grains there is a particular interest in the regulatory mechanisms of carotenoid biosynthesis in non-green plant tissues (Farré et al, 2011)
We focus on carotenoid metabolism and regulation in non-green plant tissues, as well as genetic manipulation in staple cereals including rice, maize, and wheat
Summary
Carotenoids are mainly C40 isoprenoids comprising a large family with more than 700 members that are widely distributed in plants, algae, fungi, and bacteria (Khoo et al, 2011). Carotenoids play a critical role in animal and human health. The genetic manipulation of carotenoid accumulation in staple cereal grains should be a powerful means to combat vitamin A deficiency, and especially important for developing countries where people frequently rely on a single crop for sustenance. For better genetic manipulation of carotenoid content within cereal grains there is a particular interest in the regulatory mechanisms of carotenoid biosynthesis in non-green plant tissues (Farré et al, 2011). We focus on carotenoid metabolism and regulation in non-green plant tissues, as well as genetic manipulation in staple cereals including rice, maize, and wheat. The extensive literature on carotenoid biosynthesis in bacteria or other plants is discussed, as it contributes to a better understanding of the pathway in cereals
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