Fine mapping and candidate gene analysis of a major QTL for oil content in the seed of Brassica napus

Brassica napus is one of the most important oil crops in the world, and enhancing seed oil content is an important goal in its genetic improvement. However, the underlying genetic basis for the important trait remains poorly understood in this crop. We previously identified a major locus, OILA5 responsible for seed oil content on chromosome A5 through genome-wide association study. To better understand the genetics of the QTL, we performed fine mapping of OILA5 with a double haploid population and a BC3F2 segregation population consisting of 6227 individuals. We narrowed down the QTL to an approximate 43 kb region with twelve annotated genes, flanked by markers ZDM389 and ZDM337. To unveil the potential candidate gene responsible for OILA5, we integrated fine mapping data with transcriptome profiling using high and low oil content near-isogenic lines. Among the candidate genes, BnaA05G0439400ZS was identified with high expression levels in both seed and silique tissues. This gene exhibited homology with AT3G09840 in Arabidopsis that was annotated as cell division cycle 48. We designed a site-specific marker based on resequencing data and confirmed its effectiveness in both natural and segregating populations. Our comprehensive results provide valuable genetic information not only enhancing our understanding of the genetic control of seed oil content but also novel germplasm for advancing high seed oil content breeding in B. napus and other oil crops.