Functional analysis of a bitter gustatory receptor highly expressed in the larval maxillary galea of Helicoverpa armigera

PLoS Genet. 2022 Oct 7;18(10):e1010455. doi: 10.1371/journal.pgen.1010455. eCollection 2022 Oct.

Abstract

Many plant secondary substances are feeding deterrents for insects and play a key role in the selection of host plants. The taste sensilla of phytophagous insects contain gustatory sensory neurons sensitive to deterrents but the molecular basis of deterrent chemoreception remains unknown. We investigated the function of Gr180, the most highly expressed bitter gustatory receptor in the maxillary galea of Helicoverpa armigera larvae. Functional analyses using the Xenopus oocyte expression system and two-electrode voltage clamp revealed that the oocytes expressing Gr180 responded to coumarin. Tip recording results showed that the medial sensilla styloconica of the maxilla of fifth instar larvae exhibited electrophysiological responses to coumarin. Two-choice feeding bioassays confirmed that coumarin inhibited larval feeding. A homozygous mutant strain of H. armigera with truncated Gr180 proteins (Gr180-/-) was established using the CRISPR-Cas9 system. The responses of the medial sensilla styloconica in Gr180-/- to coumarin were almost abolished, and the responses to sinigrin and strychnine were also significantly decreased. Knockout of Gr180 alleviated the feeding deterrent effects of coumarin, sinigrin, and strychnine. Thus, we conclude that Gr180 is a receptor responding to coumarin,and also participates in sensing sinigrin and strychnine. These results enhance our understanding of the gustatory sensing mechanisms of phytophagous insects to deterrents.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Coumarins / metabolism
  • Coumarins / pharmacology
  • Larva / metabolism
  • Maxilla / metabolism
  • Moths* / genetics
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism
  • Strychnine / metabolism
  • Strychnine / pharmacology
  • Taste* / genetics

Substances

  • sinigrin
  • Strychnine
  • Receptors, Cell Surface
  • Coumarins

Grants and funding

This work was supported by the National Natural Science Foundation of China (Grant No. 31830088 and 32130090; URL: www.nsfc.gov.cn) to C-ZW and Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDPB16) to C-ZW; URL: https://prp.cas.cn/#/specialIntroduction. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.