Sequencing U's Triangle: Update and Insights from the B and C Genomes

U’s triangle describes the relationship between six common Brassica species, which together contribute almost all of the world’s Brassica crops.  Although largely determined through cytological means in the 1930’s, U’s triangle has proved robust with confirmation being provided initially by early generation marker technology and more latterly by next generation sequencing technology. The close relationship between the A and C genomes of B. rapa and B. oleracea, respectively, had been well established through genetic mapping and the relative ease with which their chromosomes pair.  The B genome of B. nigra falls in a separate lineage to the A/C genomes and although it was shown to share some homology with the A/C genomes at the genetic level, it was also known to be recalcitrant to inter-specific gene transfer, which was speculated to result from divergence at the sequence level. The three diploid species that form the apices of U’s triangle have now each been sequenced allowing a more detailed comparison of their genomes. The generation of the B genome sequence assembly, and the results from the inter-genomic analyses in the context of Brassica genome evolution, will be described.