Nat. Genet http://doi.org/bqr3 (2016)
The allopolyploid crop Brassica juncea, varieties of which are grown both for their leaves and for seed oil, was derived from the hybridization between diploid ancestors, B. rapa and B. nigra. Jinghua Yang, at Zhejiang University, China, and colleagues have assembled the genome of B. juncea, providing insights into the evolutionary processes behind the origination and trait differentiation of this important species.
Combining shotgun and single-molecule sequencing techniques, the researchers obtained a well-assembled genome of B. juncea, anchored to pseudochromosomes. The genome of B. nigra was also assembled using shotgun reads. The A genomes of the allopolyploids B. juncea and B. napus appear to be of different geographic origins. However, the A subgenomes of all B. juncea varieties have a single ancestor, shown by phylogenetic and principal component analyses based on resequencing data of multiple B. juncea, B. napus and B. rapa accessions.
Scans for selective sweeps identified 794 genes selected between vegetable- and oil-use B. juncea varieties. The unexpected high proportion (36%) of the selected genes displaying homoeolog expression dominance implies its role in trait improvement. For example, homoeologue expression dominance is associated with the selection of glucosinolate and lipid metabolism genes of the vegetable and oilseed B. juncea varieties, respectively.
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Journal of the Royal Society of New Zealand (2020)