Genotypic variation of tocopherol content in a representative genetic population and genome-wide association study on tocopherol in rapeseed (Brassica napus)

Tocopherols (Tocs) are a kind of lipid-soluble substance required for the normal physiological function of mammals, particularly their antioxidant capacity. Rapeseed (Brassica napus) oil is an important source of exogenous Tocs. However, the genotypic differences in the total Toc contents, the Toc composition in the seeds, and the molecular markers associated with the seed Toc remain largely unknown. Here, we selected 290 rapeseed accessions based on the resequencing of 991 genomes in a worldwide collection of rapeseed germplasm. The contents of the four Toc isoforms, namely, alpha-, beta-, gamma-, and delta-Tocs, were also measured. Results show that the total Toc content and the gamma-/alpha-Toc ratio varied greatly across the accessions from 85.34 to 387.00 mg/mg and 0.65 to 5.03, respectively. Furthermore, we conducted genome-wide association studies on the Tocs, which identified 28 and 73 single nucleotide polymorphisms significantly associated with the variation of total Toc content and gamma-/alpha-Toc ratio, respectively. Bna.C02.VTE4, a putative orthologue of Arabidopsis VITAMIN E DEFICIENT 4, was tightly associated with the gamma-/alpha-Toc ratio. This study recommends specific genetic materials with particularly high total Toc and/or low gamma-/alpha-Toc ratio and the molecular markers and haplotypes associated with these quality traits for rapeseed breeding.