Genetic dissection of tocopherol content and composition in maize grain using quantitative trait loci analysis and the candidate gene approach

Tocopherols are essential micronutrients for humans and animals, with several beneficial effects in plants. Among cereals, only maize grains contain high concentrations of tocopherols. In this investigation we analyzed, during 2004 and 2005, by high-performance liquid chromatography (HPLC), a population of 233 recombinant inbred lines (RIL) which were derived from two diverse parents and had extremely variable tocopherol content and composition. A genetic map was constructed using 208 polymorphic molecular markers including gene-targeted markers based on six candidate genes of the tocopherol biosynthesis pathway (HPPD, VTE1, VTE3, VTE4, P3VTE5, and P4VTE5). Thirty-one quantitative trait loci (QTL) associated with quantitative variation of tocopherol content and composition were identified by composite interval mapping (CIM); these were located on sixteen genomic regions covering all the chromosomes except chromosome 4. Most (65%) QTL were co-located, suggesting that in some cases the same QTL predominantly affected the amounts of more than one tocopherol. Two candidate genes, HPPD and VTE4 showed co-localization with major QTL for tocopherol content and composition whereas only one interval (umc1075-umc1304) on chromosome eight exhibited a QTL for alpha, delta, gamma, and total tocopherols with high LOD and PVE values. The candidate genes associated with tocopherol content and with composition, especially VTE4 and HPPD, could be precisely used for alteration of the tocopherol content and composition of maize grains by development of functional markers. Other identified major QTL especially those on chromosomes 8, 1, and 2 (near candidate gene VTE5) can also be used for improvement of maize grain quality by marker-assisted selection.