Organization of the genome sequence of the polyploid crop species Brassica juncea
- Nature Genetics
- A draft genome sequence of Brassica juncea, a member of the Brassicaceae and therefore a species benefiting from the functional genomics advances in the ‘model’ species Arabidopsis thaliana, was reported recently by Yang et al.1 . B. juncea is a recently formed allotetraploid, whose diploid progenitors were mesohexaploids: Brassica rapa (which contributed the A genome) and Brassica nigra (which contributed the B genome). In addition to underpinning future trait-oriented work in this important crop species, which includes both vegetable and oil types, the sequences were analyzed for characteristics of genome evolution under crop selection. For both purposes, the genome sequences must represent with high fidelity (though not perfectly in ‘draft’ form) both the gene complement and gene order of the species. As a model for addressing the challenges of achieving an adequate representation of the latter for allopolyploid crops, the construction methodology employed short shotgun sequence reads, single-molecule long reads, BioNano sequencing and highresolution genetic mapping.