Abstract
BackgroundTocopherols are important antioxidants in vegetable oils; when present as vitamin E, tocopherols are an essential nutrient for humans and livestock. Rapeseed (Brassica napus L, AACC, 2 n = 38) is one of the most important oil crops and a major source of tocopherols. Although the tocopherol biosynthetic pathway has been well elucidated in the model photosynthetic organisms Arabidopsis thaliana and Synechocystis sp. PCC6803, knowledge about the genetic basis of tocopherol biosynthesis in seeds of rapeseed is scant. This project was carried out to dissect the genetic basis of seed tocopherol content and composition in rapeseed through quantitative trait loci (QTL) detection, genome-wide association analysis, and homologous gene mapping.Methodology/Principal FindingsWe used a segregating Tapidor × Ningyou7 doubled haploid (TNDH) population, its reconstructed F2 (RC-F2) population, and a panel of 142 rapeseed accessions (association panel). Genetic effects mainly contributed to phenotypic variations in tocopherol content and composition; environmental effects were also identified. Thirty-three unique QTL were detected for tocopherol content and composition in TNDH and RC-F2 populations. Of these, seven QTL co-localized with candidate sequences associated with tocopherol biosynthesis through in silico and linkage mapping. Several near-isogenic lines carrying introgressions from the parent with higher tocopherol content showed highly increased tocopherol content compared with the recurrent parent. Genome-wide association analysis was performed with 142 B. napus accessions. Sixty-one loci were significantly associated with tocopherol content and composition, 11 of which were localized within the confidence intervals of tocopherol QTL.Conclusions/SignificanceThis joint QTL, candidate gene, and association mapping study sheds light on the genetic basis of seed tocopherol biosynthesis in rapeseed. The sequences presented here may be used for marker-assisted selection of oilseed rape lines with superior tocopherol content and composition.
Highlights
Vitamin E is an essential micronutrient for humans and mammals, which have no ability to synthesize it
Moderate differences were observed between Tapidor and Ningyou7 for a-tocopherol content (aTC), c-tocopherol content, total tocopherol content (TTC), and tocopherol composition (TCO)
Dozens of unique quantitative trait loci (QTL) and associated loci were detected in the bi-parental populations and the association panel for tocopherol content and composition from multiple environments, indicating that tocopherol content variation was caused by variations in many genetic loci
Summary
Vitamin E is an essential micronutrient for humans and mammals, which have no ability to synthesize it. The atocopherol form is considered to have the highest nutritional value for humans and livestock [1,2,3,4]. Tocopherols are the major form of vitamin E in the seeds of dicots, but tocotrienols exist widely in the seeds of monocots [5,6]. Tocopherols are important antioxidants in vegetable oils; when present as vitamin E, tocopherols are an essential nutrient for humans and livestock. PCC6803, knowledge about the genetic basis of tocopherol biosynthesis in seeds of rapeseed is scant This project was carried out to dissect the genetic basis of seed tocopherol content and composition in rapeseed through quantitative trait loci (QTL) detection, genome-wide association analysis, and homologous gene mapping
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