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Genetic Basis of Tocopherol Accumulation in Soybean (Glycine Max [L.] Merr.) Seeds

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Title: Genetic Basis of Tocopherol Accumulation in Soybean (Glycine Max [L.] Merr.) Seeds
Author: Shaw, Eric
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: Rajcan, Istvan
Abstract: This thesis is an investigation of the genetic basis of tocopherol accumulation in soybean (Glycine max [L.] Merrill) seeds. Soybean is the world’s most widely grown protein and oilseed crop and the principle source of vitamin E (tocopherols) as a supplement. Tocopherols (α-, β-, γ- and δ-isomers) are powerful antioxidants that contain human health benefits, including a decrease in the risk of lung cancer, heart disease and osteoporosis. The purpose of this research was to identify genetic and biochemical components affecting tocopherol accumulation in soybean seeds. The objectives were to: 1) investigate location and year effects on soybean seed tocopherol levels in the field; 2) determine environmental factors affecting soybean seed tocopherol levels under controlled conditions; 3) identify simple sequence repeat (SSR) markers that tag quantitative trail loci (QTL) for individual and total tocopherols; and 4) evaluate the potential role of VTE1, VTE3 and VTE4 genes in tocopherol accumulation using the candidate gene approach. Seventy nine recombinant inbred lines (RILs) derived from the cross between OAC Bayfield and OAC Shire were grown in the field at Elora, Woodstock and St. Pauls, ON, in 2009 and 2010. The tocopherol components were quantified using high performance liquid chromatography (HPLC). The results showed a significant (p < 0.001) genotype, environment and genotype x environment effect for each tocopherol component. It was discovered that a 2 x phosphate fertilizer (K2SO4 at 1.0M/150mL) and 30 ˚C temperature treatment increased each tocopherol component, whereas drought had no effects. Single marker analysis identified 42 QTL and interval mapping identified 26 QTL across 17 chromosomes. Significant two-locus epistatic interactions were found with a total of 122 and 152 in the 2009 and 2010 field seasons, respectively. The multiple locus models explained 18.4% to 72.2% with an average of 45.7% of the total phenotypic variation. The candidate gene approach using nucleotide sequences from the coding regions identified two single nucleotide polymorphisms (SNPs) in VTE1, five SNPs in VTE4 and none in VTE3. The SNPs were predicted to cause functional protein changes and the genes co-localized with some of the identified QTL. The results of this study provide a better understanding of the environmental factors and genetic mechanisms that influence the accumulation of tocopherols in soybean seeds.
Date: 2012-09
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