Expansion of a bitter taste receptor family in a polyphagous insect herbivore.

Wei Xu,Alisha Anderson,Alexie Papanicolaou,Hui-Jie Zhang

doi:10.1038/srep23666

Abstract

The Insect taste system plays a central role in feeding behaviours and co-evolution of insect-host interactions. Gustatory receptors form the interface between the insect taste system and the environment. From genome and transcriptome sequencing we identified 197 novel gustatory receptor (GR) genes from the polyphagous pest Helicoverpa armigera. These GRs include a significantly expanded bitter receptor family (180 GRs) that could be further divided into three categories based on polypeptide lengths, gene structure and amino acid sequence. Type 1 includes 29 bitter Gr genes that possess introns. Type 2 includes 13 long intronless bitter Gr genes, while Type 3 comprises 131 short intronless bitter Gr genes. Calcium imaging analysis demonstrated that three Type 3 GRs (HarmGR35, HarmGR50 and HarmGR195) can be activated by a crude extract of cotton leaves. HarmGR195, a GR specifically and selectively expressed in adult tarsi, showed a specific response to proline, an amino acid widely present in plant tissues. We hypothesise that the expansion in the H. armigera GR family may be functionally tied to its polyphagous behavior. Understanding the molecular basis of polyphagy may provide opportunities for the development of new environmentally friendly pest control strategies.

Highlights

Chemosensory receptors represent an interface between an insect and its chemical environment, mediating pivotal biological processes such as host finding, mate selection and choice of oviposition sites[1]
A bioinformatics screen of the H. armigera genome and transcriptome data revealed a total of 197 gustatory receptor (GR) and 64 odorant receptor (OR) genes (Fig. 1A)
In comparison with all insect species with currently available genomes, H. armigera showed the second highest number of GRs, 197. This is the highest number of GRs identified in a lepidopteran genome with only the red flour beetle T. castaneum having more, 220 (Fig. 1A)

Summary

Introduction

Chemosensory receptors represent an interface between an insect and its chemical environment, mediating pivotal biological processes such as host finding, mate selection and choice of oviposition sites[1]. The gustatory receptors (GRs), plays a central role in co-ordinating insect feeding behaviours[1]. Insect Gr genes were first identified from the Drosophila melanogaster genome[2]. They have been classified into four clades: CO23, GR43a-like[4], sugar[5,6,7,8,9,10] and bitter[11,12]. We utilized genome and transcriptome data from H. armigera and manually identified this species repertoire of Gr genes. Comparative gene expression, and topological and calcium imaging analyses to structurally and functionally characterize the GR repertoire, in the process uncovering a markedly expanded family of lepidopteran GRs

Methods

Results

Conclusion