Genetic analysis of variation for carotenoids and tocopherols in maize

Carotenoids and tocopherols are two classes of compounds present in maize (Zea mays L.) which may add value to the grain. Both the carotenoids and tocopherols are fat soluble antioxidant vitamins. The vitamin and antioxidant properties of the carotenoids and tocopherols provide health and economic benefits which potentially could be captured by both producers and consumers. β-carotene and α-tocopherol have the highest biological activity for the carotenoids and the tocopherols, respectively. However, neither of these compounds is in high concentration in maize kernels. The objective of this research was to gain basic genetic information about the chromosomal regions with quantitative trait loci (QTL) controlling carotenoid and tocopherol accumulation in maize kernels using molecular markers. Once the QTL are identified and validated, they could be used in a marker assisted selection program to facilitate increasing levels of these antioxidant vitamins in maize grain. Three sets of materials were assayed in this research (W64a x A632) F _2:4 mapping population, testcross progeny with AE335, and (IHO90 x B73) B73 BC₁S₁ mapping population. Molecular markers were evaluated on the F_2:4 and BC₁S₁ populations, and linkage maps were created. Each population was analyzed for four carotenoids, β-carotene, β-cryptoxanthin, lutein, and zeaxanthin and three tocopherols, α-tocopherol, δ-tocopherol, and γ-tocopherol. Composite Interval Mapping was used to identify QTL. Total carotenoids and total tocopherols were calculated to identify QTL with affects on the total concentration of carotenoids or tocopherols. Ratio (α/γ) tocopherol was analyzed to identify QTL influencing the conversion of γ-tocopherol to α-tocopherol. For the tocopherols, two chromosomal regions with QTL on chromosomes 1 and 5 were significant for the three sets of materials. For the carotenoids three regions with QTL on chromosomes 6, 7, and 8 were significant across populations. Two of the three QTL map to regions with candidate genes possibly responsible for quantitative variation in the carotenoids, yellow1 and viviparous9. yellow1 maps to chromosome six and is associated with the gene phytoene synthase, the first step in the carotenoid biosynthetic pathway. viviparous9 maps to chromosome seven, and is associated with ζ-carotene desaturase, another enzyme early in the biosynthetic pathway of the carotenoids.