UC Davis

Brassica napus, a globally important oilseed crop, is an allotetraploid hybrid species with two subgenomes originating from Brassica rapa and Brassica oleracea. The presence of two highly similar subgenomes has made the assembly of a complete draft genome challenging and has also resulted in natural homoeologous exchanges between the genomes, resulting in variations in gene copy number, which further complicates assigning sequences to correct chromosomes. Despite these challenges, high-quality draft genomes of this species have been released. Using third generation sequencing and assembly technologies, we generated a new genome assembly for the synthetic B. napus cultivar Da-Ae. Through the use of long reads, linked-reads, and Hi-C proximity data, we assembled a new draft genome that provides a high-quality reference genome of a synthetic B. napus. In addition, we identified potential hotspots of homoeologous exchange between subgenomes within Da-Ae, based on their presence in other independently derived lines. The occurrence of these hotspots may provide insight into the genetic rearrangements required for B. napus to be viable following the hybridization of B. rapa and B. oleracea.