Phylogenetic analysis of a collection of Brassica genomes
reveals Chinese flowering cabbage has a closer evolutionary relationship
with the diploid progenitor of the allotetraploid species, B.
juncea
The Brassicaceae family serves as a useful model for studying polyploidy
and chromosome evolution. The evolutionary relationship of six
ecologically important Brassica species including three diploid
species (B. rapa , B. oleracea , and B. nigra ) and
three allotetraploid species (B. napus , B. juncea , andB. carinata ) was well described in a classical U triangle
model(Cheng et al., 2016) .
To elucidate the evolutionary distance of the current Chinese flowering
cabbage genome to other Brassica genomes, we constructed a
phylogenetic tree (Fig. 4) for 12 collected Brassica genomes and
eight related Brassicaceae species using the coding sequences of 434
single-copy genes that are present in all of the species. The result
shows that the three Brassica genome types are clearly separated
from each other among the investigated species. The current Chinese
flowering cabbage has a AA genome type which is closer to the AA genome
of the allotetraploid species, B. juncea , than the AA genome of
another B. rapa line, B. rapa var pekinensis in the
phylogenetic tree, suggesting Chinese flowering cabbage is
evolutionarily closer to the diploid progenitor of the allotetraploid
species, Brassica juncea . Also, in the CC genome clade, B.
oleracea var capitata was clustered firstly with two B.
napus CC genomes and then with B. oleracea var italica ,
implying B. oleracea var capitata has a CC genome that is
closer to the donor of CC genome of the B. napus . Similarly,B. rapa Z1 was clustered firstly with B. napus AA genome
and then other AA genomes, pointing to it as being evolutionarily closer
to the AA genome progenitor of B. napus .