A highly contiguous genome assembly ofBrassica nigra(BB) and revised nomenclature for the pseudochromosomes

AbstractBrassica nigra(BB), also called black mustard, is grown as a condiment crop in India.B. nigrarepresents the B genome of U’s triangle and is one of the progenitor species ofB. juncea(AABB), an important oilseed crop of the Indian subcontinent. We report here a highly contiguous genome assembly ofB. nigravariety Sangam. The genome assembly has been carried out using Oxford Nanopore long-read sequencing and optical mapping. The resulting chromosome-scale assembly is a significant improvement over the previous draft assemblies ofB. nigra; five out of the eight pseudochromosomes were represented by one scaffold each. The assembled genome was annotated for the transposons, centromeric repeats, and genes. TheB. nigragenome was compared with the recently available contiguous genome assemblies ofB. rapa(AA),B. oleracea(CC), andB. juncea(AABB). Based on the maximum homology among the three diploid genomes of U’s triangle, we propose a new nomenclature forB. nigrapseudochromosomes, taking theB. rapapseudochromosome nomenclature as the reference.