Evolução molecular e padrões de expressão de genes da família das proteínas ligantes a odores (OBPs) em duas espécies de moscas-das-frutas do grupo Anastrepha fraterculus
Resumen
Odorant-binding proteins (OBPs) are of great importance for survival and reproduction
since they participate in initial steps of the olfactory signal transduction cascade,
solubilizing and transporting chemical signals to the olfactory receptors. A comparative
analysis of OBPs between closely related species may help explain how these genes
evolve and are maintained under natural selection and how differences in these proteins
can affect olfactory responses, and consequently lead to species differentiation. We
studied OBP genes in the closely related species Anastrepha fraterculus and Anastrepha
obliqua, which, albeit generalists, have different host preferences, using transcriptomes
and real time quantitative PCR data. We identified 24 different OBP sequences from
Anastrepha fraterculus and 25 from A. obliqua, which correspond to 21 Drosophila
melanogaster OBP genes. Phylogenetic analysis separated Anastrepha OBPs sequences
in four branches that represent four subfamilies: classic, minus-C, plus-C and dimer. We
found evidence of positive selection in three classic subfamily genes OBP56h-1,
OBP56h-2 e OBP57c and in the plus-C subfamily gene OBP50a, and at least one
duplication event that preceded the speciation of these two species. Four positively
selected sites putatively resulted in radical changes in amino acid properties. Inferences
on tertiary structures of putative proteins from these genes revealed that at least one
positively selected change involves the binding cavity (the odorant binding region) in the
plus-C OBP50a, which is important because changes in the binding cavity could change
OBPs specificity. Differential gene expression analysis at different reproductive stages
showed that all nine OBP genes tested were significantly differentially expressed between
A. fraterculus and A. obliqua at several reproductive profiles, but OBP56a, OBP56d,
OBP57c and both OBP56h paralogs showed the highest differences in expression levels.
The results generated in this study indicated that at least seven OBP genes may be
involved in the A. fraterculus e A. obliqua differentiation, and in the fraterculus group
differentiation as well.