Genome Evolution after Whole Genome Triplication: the Subgenome Dominance in Brassica rapa

Subgenome dominance is widely existed in plant species that experienced allopolyploidization. Subgenome dominance represents a series of biased pehnomenons as that one subgenome retains more genes, more dominantly expressed genes, less functional mutations etc., over the other subgenomes. Brassica rapa, which experienced a whole genome triplication (WGT) event ~11 million years ago, exhibits significant subgenome dominance, with the LF (the least fractionated) subgenome retains ~1.5 times more genes in average than the other two subgenomes MF1 and MF2 (more fractionated 1 and 2). Furthermore, paralogous genes in LF are always expressed to higher levels and accumulated less functional mutations than that located at MF1 and MF2. Further research found that small RNA mediated methylation of transposons that distributed at genes’ flanking regions plays an important role in the formation of subgenome dominance. Finally, based on these findings, a two-step process was proposed to illustrate the WGT event in B. rapa.