The Road to Biofortification: Progress and Prospects for Orange, High Provitamin Α Maize.

The improvement of crop nutritional quality through breeding, termed biofortification, is advocated as a low-cost, sustainable approach to address micronutrient deficiencies worldwide, especially vitamin A, iron, and zinc. In particular, efforts are ongoing in multiple crops to develop varieties with increased levels of provitamin A carotenoids. With considerable variation in grain carotenoid composition, maize is an important staple that could have pervasive impact in the global South where vitamin A deficiency is prevalent. Through a genome-wide association study (GWAS) of the maize nested association mapping (NAM) and the Goodman-Buckler inbred association panels, we detected associations between several candidate genes relevant to the biosynthesis and retention of carotenoids and quantitative levels of carotenoids in grain. As a corollary, results from an analysis of RNA-seq data derived from a catalog of six stages of grain development across the NAM founder lines revealed that genetic control of carotenoid composition is largely regulated at the transcriptional level. In addition, we demonstrated the accuracy of prediction models built on marker sets with different levels of genome coverage for predicting carotenoid levels in the inbred association panel. Given the findings from GWAS and genomic prediction studies, we outline a flexible strategy to rapidly convert elite white- or yellow-grain germplasm to orange varieties with high levels of provitamin A.