Mapping loci controlling fatty acid profiles, oil and protein content by genome-wide association study in Brassica napus

Optimizing the profile and quantity of fatty acids in rapeseed (Brassica napus L.) is critical for maximizing the value of edible oil and biodiesel. However, selection of these complex seed quality traits is difficult before haplotypes controlling their contents are identified. To efficiently identify genetic loci influencing these traits and underlying candidate genes and networks, we performed a genome-wide association study (GWAS) of eight seed quality traits (oil and protein content, palmitic, stearic, oleic, linoleic, eicosenoic and erucic acids content). The GWAS population comprised 370 diverse accessions, which were phenotyped in five environments and genotyped using 60K SNP arrays. The results indicated that oil and protein contents generally showed negative correlations, while fatty acid contents showed positive or negative correlations, with palmitic and erucic acid contents directly affecting oil content. Seven SNPs on five chromosomes were associated with both seed oil and protein content, and five genes orthologous to genes in Arabidopsis thaliana were predicted as candidates. From resequencing data, besides known haplotypes in BnaA.FAE1.a and BnaC.FAE1.a, three accessions harboring a new haplotype conferring moderate erucic acid content were identified. Interestingly, in a haplotype block, one haplotype was associated with high palmitic acid content and low oil content, while the others showed the reverse effects. This finding was consistent with a negative correlation between palmitic acid and oil contents, suggesting historical selection for high oil content. The identification by this study of genetic variation and complex correlations of eight seed quality traits may be beneficial for crop selection strategies.