Molecular evolution of Odorant-binding proteins gene family in two closely related Anastrepha fruit flies.

Emeline Boni Campanini,Reinaldo Alves De Brito

doi:10.1186/s12862-016-0775-0

Emeline Boni Campanini, Reinaldo Alves De Brito

Open Access

https://doi.org/10.1186/s12862-016-0775-0

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Journal: BMC ecology	Publication Date: Oct 7, 2016
Citations: 22	License type: cc-by

Affiliation: Universidade Federal de São Carlos

Abstract

BackgroundOdorant-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. We studied OBP genes in the closely related species Anastrepha fraterculus and A. obliqua, which have different host preferences, using data from RNA-seq cDNA libraries of head and reproductive tissues from male and female adults, aiming to understand the speciation process occurred between them.ResultsWe identified 23 different OBP sequences from Anastrepha fraterculus and 24 from A. obliqua, which correspond to 20 Drosophila melanogaster OBP genes. Phylogenetic analysis separated Anastrepha OBPs sequences in four branches that represent four subfamilies: classic, minus-C, plus-C and dimer. Both species showed five plus-C members, which is the biggest number found in tephritids until now. We found evidence of positive selection in four genes and at least one duplication event that preceded the speciation of these two species. 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.Conclusions A. fraterculus and A. obliqua have a bigger OBP repertoire than the other tephritids studied, though the total number of Anastrepha OBPs may be larger, since we studied only a limited number of tissues. The contrast of these closely related species reveals that there are several amino acid changes between the homologous genes, which might be related to their host preferences. The plus-C OBP that has one amino acid under positive selection located in the binding cavity may be under a selection pressure to recognize and bind a new odorant. The other positively selected sites found may be involved in important structural and functional changes, especially ones in which site-specific changes would radically change amino acid properties.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0775-0) contains supplementary material, which is available to authorized users.

Highlights

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
OBP genes in Anastrepha fraterculus and Anastrepha obliqua We identified a similar number of sequences associated with OBPs in the two species: different sequences in A. fraterculus and in A. obliqua, which corresponded to 20 different D. melanogaster OBP genes (Table 1)
We found great similarity in amino acid and DNA sequences among orthologous OBPs in A. fraterculus and A. obliqua, which may be a reflection of their recent divergence or evolutionary conservatism

Summary

Introduction

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. The study of the genetics of species differences generally requires the identification of fixed genes between lineages. The solubilization and transport of chemical signals through the aqueous lymph of insect’s sensilla to the olfactory receptors is the initial step of the transduction cascade of olfactory signals, and is mediated by the Odorantbinding proteins – OBPs [10]. It is expected that more generalist species would have a larger OBP repertoire to recognize various plant chemicals, in contrast to more specialist species, in which the power of natural selection to maintain a large OBP repertoire may have been weaker [20]

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