Rapid evolution of two odorant-binding protein genes, Obp57d and Obp57e, in the Drosophila melanogaster species group

Genes encoding odorant-binding protein (OBP) form a large family in an insect genome. Two OBP genes, Obp57d and Obp57e, were previously identified to be involved in host-plant recognition in Drosophila sechellia. Here, by comparing the genomic sequences at the Obp57d/e locus from 27 Drosophila species, we found large differences in gene number between species. Phylogenetic analysis indicates that Obp57d and Obp57e in the Drosophila melanogaster species group arose by gene duplication of an ancestral OBP gene that remains single in the obscura species group. Further gain and loss of OBP genes were observed in several lineages in the melanogaster group. Site-specific analysis of evolutionary rate suggests that Obp57d and Obp57e have functionally diverged from each other. Thus, there are two classes of gene number differences in the Obp57d/e region: the difference of the genes at the early stage of evolution after gene duplication, and the difference of the genes that have functionally diverged from each other. Our analyses demonstrate that these two classes of differences can be distinguished by comparisons of many genomic sequences from closely related species.

Key Words: functional divergence, gene duplication, gene number difference

Online ISS 1091-6490
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