Abstract

Lepidopteran pheromone receptors (PRs), for which orthologies are evident among closely related species, provide an intriguing example of gene family evolution in terms of how new functions may arise. However, only a limited number of PRs have been functionally characterized so far and thus evolutionary scenarios suffer from elements of speculation. In this study we investigated the turnip moth Agrotis segetum, in which female moths produce a mixture of chemically related pheromone components that elicit specific responses from receptor cells on male antennae. We cloned nine A. segetum PR genes and the Orco gene by degenerate primer based RT-PCR. The nine PR genes, named as AsegOR1 and AsegOR3-10, fall into four distinct orthologous clusters of known lepidopteran PRs, of which one contains six paralogues. The paralogues are under relaxed selective pressure, contrasting with the purifying selection on other clusters. We identified the receptors AsegOR9, AsegOR4 and AsegOR5, specific for the respective homologous pheromone components (Z)-5-decenyl, (Z)-7-dodecenyl and (Z)-9-tetradecenyl acetates, by two-electrode voltage clamp recording from Xenopus laevis oocytes co-expressing Orco and each PR candidate. These receptors occur in three different orthologous clusters. We also found that the six paralogues with high sequence similarity vary dramatically in ligand selectivity and sensitivity. Different from AsegOR9, AsegOR6 showed a relatively large response to the behavioural antagonist (Z)-5-decenol, and a small response to (Z)-5-decenyl acetate. AsegOR1 was broadly tuned, but most responsive to (Z)-5-decenyl acetate, (Z)-7-dodecenyl acetate and the behavioural antagonist (Z)-8-dodecenyl acetate. AsegOR8 and AsegOR7, which differ from AsegOR6 and AsegOR1 by 7 and 10 aa respectively, showed much lower sensitivities. AsegOR10 showed only small responses to all the tested compounds. These results suggest that new receptors arise through gene duplication, and relaxed evolutionary constraints or positive selection among paralogues allow functional divergence to occur in spite of purifying selection being the norm.

Highlights

  • Sex pheromone communication in moths, which involves the production of specific sex pheromones in females and the corresponding selective detection and response by pheromone receptors (PRs) in conspecific male antennae, has long been the intriguing subject for evolutionary studies

  • Based on these findings and analysis of selection operating on the different genes, we propose a possible scenario for the functional evolution of the pheromone receptor multigene family in moths

  • Nine candidate pheromone receptor genes and Orco gene cloned from A. segetum

Read more

Summary

Introduction

Sex pheromone communication in moths, which involves the production of specific sex pheromones in females and the corresponding selective detection and response by pheromone receptors (PRs) in conspecific male antennae, has long been the intriguing subject for evolutionary studies. Previous studies have shown that the pheromone production can evolve both by gene duplication followed by structural mutations in the gene coding region [1,2,3,4] and by differential regulation in the expression of a standing set of genes [5,6]. It remains a conundrum how the corresponding variation in male detection and response originates and evolves. As a limited number of insect PR genes have been deorphaned, the functional evolution of the receptors remains poorly understood and little is known about how sequence changes are associated with changes in ligand specificity or sensitivity

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call