<italic>EXO70</italic> gene duplication and divergent evolution in <italic>Brassica oleracea</italic> and <italic>B. rapa</italic>

Abstract

To understand <italic>EXO70</italic> gene duplication in <italic>Brassica rapa</italic> and <italic>B. oleracea</italic> genomes, we identified and analyzed 39 <italic>BrEXO70</italic> and 45 <italic>BoEXO70</italic> genes. <italic>EXO70s</italic> from <italic>B. rapa</italic> show the same pattern of high interspecies conservation as those from <italic>B. oleracea</italic>. The number of exons differs among <italic>EXO70</italic> genes, with the greatest number observed in <italic>EXO70A</italic>. Although each encoded EXO70 contains a highly conserved pfam03081 domain, the domains differ from one another in amino acid composition. The gene duplication mechanism of <italic>BoEXO70</italic> is more complex than that of <italic>BrEXO70</italic>. Although few differences in synonymous codon preference exist between <italic>BoEXO70</italic> and <italic>BrEXO70</italic>, obvious differences in codon preference are present among different <italic>EXO70</italic> types. We conclude that <italic>EXO70</italic> has been duplicated multiple times during the evolution of both <italic>B. rapa</italic> and <italic>B. oleracea</italic>. More duplications have occurred in <italic>B. oleracea</italic> than in <italic>B. rapa</italic>, even though the same modes of gene duplication are found in both <italic>BoEXO70</italic> and <italic>BrEXO70</italic>. In addition, high conservation is exhibited by the same types of <italic>EXO70</italic> genes in both <italic>B. oleracea</italic> and <italic>B. rapa</italic>. We also propose that the pfam03081 domain plays an essential role in EXO70 functional determination. Finally, <italic>EXO70</italic> evolutionary divergence is evident in both <italic>B. rapa</italic> and <italic>B. oleracea</italic>.