Joint Linkage-Association Mapping Identifies Genes Associated with Provitamin A and Vitamin E Content In Maize Kernel.

Maize is a primary food source for millions of people in the developing world.  However, this crop by itself does not provide adequate levels of vitamin A and E nutrition.  Consequently, vitamin A deficiency (VAD) and to a lesser extent, vitamin E deficiency (VED) are serious problems that affect many people.  Some examples of health-related issues that arise from these nutritional deficiencies include eventual blindness (from VAD) and neuromuscular problems (from VED). One solution for reducing VAD and VED is to increase the amount of provitamin A and vitamin E in the maize kernel.  These compounds naturally occur in maize, specifically in carotenoids (e.g. β-carotene) and tocopherhols (e.g., α-tocopherol), respectively.  This research uses joint linkage-association mapping methodologies to identify genes and alleles associated with kernel carotenoid and tocopherol levels.  Breeders can then use marker assisted selection to select on superior alleles and develop lines with increased vitamin content. This work focuses on identifying significant associations for approximately 1.6 million SNPs across the genome in the maize nested association mapping (NAM) population.  A stepwise model selection procedure is combined with a resampling scheme to empirically determine the robustness of our results to random genotypic and phenotypic fluctuations. To date, we reconfirmed two biosynthetic genes that are associated with elevated provitamin A carotenoids, and one biosynthetic gene that is associated with α-tocopherol.  The ultimate goal of this research is to identify enough genes to develop maize lines with 15 µg/g of β-carotene and 30 to 60 µg/g of α-tocopherol.  These amounts should result in enough vitamin A and E to meet the Daily Recommended Intake (DRI) levels specified by the National Academy Panel.