ARS | Publication request: Rare Genetic Variation at Zea mays crtRB1 Increases B-Carotene in Maize Grain

Submitted to: Nature Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2010
Publication Date: March 21, 2010
Citation: Yan, J., Kandianis, C.B., Haries, C.E., Bai, L., Kim, E., Yang, X., Skinner, D., Fu, Z., Mitchell, S., Li, Q., Fernandez, M., Zaharieva, M., Babu, R., Fu, Y., Palacios, N., Li, J., DellaPenna, D., Brutnell, T., Buckler, E.S., Warburton, M.L., Rocheford, T. 2010. Rare Genetic Variation at Zea mays crtRB1 Increases B-carotene in Maize Grain. Nature Genetics. 42:322-329.

Interpretive Summary: Blindness and disease caused by a deficiency of vitamin A is a problem for millions of children in the developing world, and may be easily reduced by increasing the content of provitamin A in maize grains. Provitamin A is converted to vitamin A in the human body, and the world’s poorest populations eat a disproportionate amount of staple cereals compared to fruits and vegetables; therefore, making the staple grains, such as maize, healthier would be a cheap and efficient way to address this problem. There is genetic variation for increased provitamin A in maize, but the best genes for this trait have only now been discovered using new techniques. This paper uses one of these new techniques (association mapping) to identify a gene that greatly increases provitamin A content in the maize grains; in addition, this study confirms these results using three independent techniques (QTL mapping, gene expression, and transient assays in E. coli). Finally, and very importantly, this study identifies which maize lines have the favorable forms of this new gene and of a previously reported gene. Because the most favorable form of each gene was found in diverse corn cultivars that are very rarely crossed in maize breeding programs, we further provide the markers that can most rapidly move these favorable forms into modern maize for human consumption.

Technical Abstract: Breeding to increase b-carotene levels in cereal grains, termed Provitamin A biofortification, is an economical approach to address the challenge of dietary vitamin A deficiency in the developing world. We draw upon experimental evidence from DNA sequence, transcriptional expression, and recombinant protein activity to demonstrate that the maize b-carotene hydroxylase 1 (ZmCrtR-B1) gene underlies an important quantitative trait locus associated with the concentration of b-carotene in maize kernels. ZmCrtR-B1 alleles associated with reduced expression lead to decreased hydroxylation of b-carotene pools, resulting in higher concentration of b-carotene in maize grain. The most favorable ZmCrtR-B1 allele, unique to temperate germplasm and rare in frequency, is being introgressed through marker assisted selection (MAS) with inexpensive PCR markers into tropical adapted germplasm, where it is most needed for human health.