Genome triplication drove the diversification of Brassica plants

Abstract

Brassica species are significant in diversity. First, it has many close but different species, such as Brassica rapa, Brassica oleracea, Brassica nigra, Brassica napus, Brassica juncea, etc, many of which are important crops. Second, for each Brassica species, it is rich in morphotypes, they have distinctive and impressive traits, such as the heading leaves and enlarged roots in B. rapa (Chinese cabbage and turnip) or B. oleracea (cabbage and kohlrabi), and the enlarged inflorescences in B. oleracea, i.e. broccoli, cauliflower. All these Brassicas are evolved from a common hexaploidy ancestor that experienced a whole genome triplication (WGT) event. Studies show that WGT drove the diversification of Brassica plants in both the speciation and booming of morphotypes. Following WGT, the extensive block reshuffling and chromosome reduction of the triplicated diploid ancestor through rediploidization process as well as hybridization promoted the Brassica speciation. The biased gene retention and subgenome dominance effect further promoted function evolution of multi-copy genes, and finally lead to the expansion of rich morphotypes in Brassicas. Conclusively, the WGT event plays important role in driving the diversification of Brassicas by initiating the genome and gene-level evolution.