Identification of a General Odorant Receptor for Repellents in the Asian Corn Borer Ostrinia furnacalis

Abstract

Attractants and repellents are considered to be an environment-friendly approach for pest management. Odorant receptors (ORs), which are located on the dendritic membranes of olfactory sensory neurons in insects, are essential genes for recognizing attractants and repellents. In the Asian corn borer, Ostrinia furnacalis, ORs that respond to sex pheromones have been characterized, but general ORs for plant odorants, especially for repellents, have not been identified. Nonanal is a plant volatile of maize that could result in avoidance of the oviposition process for female adults in O. furnacalis. In this study, we identified a female-biased OR that responds to nonanal using a Xenopus oocyte expression system. In addition, we found that OfurOR27 was also sensitive to two other compounds, octanal and 1-octanol. Behavioral analysis showed that octanal and 1-octanol also caused female avoidance of oviposition. Our results indicated that OfurOR27 is an OR that is sensitive to repellents. Moreover, the two newly identified repellents may help to develop a chemical ecology approach for pest control in O. furnacalis.

Keywords: heterologous expression system; host plant volatile; nonanal; odorant receptor; repellent.

FIGURE 1

Functional analysis of OfurOR27 using a Xenopus oocyte expression system. (A) Responses of OfurOR27/Orco to eight identified odorants (10^{– 4} M). (B) Response profile of OfurOR27/Orco. Error bars indicate standard error of the mean [p < 0.001, ANOVA, least-significant difference (LSD), n = 6]. (C) Tuning curve for the OfurOR27/Orco to an odorant panel comprising 95 odorants, arranged along the x-axis according to the strength of the response they elicit. The odorants that elicited the strongest responses were placed near the center of the distribution, while those that elicited the weakest responses were placed near the edges. (D) Dose–response curve for OfurOR27/Orco in responding to nonanal, 1-octanol, and octanal. Error bars indicate SEM (n = 6).

FIGURE 2

Tissue-specific expression of OfurOR27 in O. furnacalis. FA, female antennae; MA, male antennae; FP, female proboscis; MP, male proboscis; FT, female thorax; MT, male thorax; FL, female legs; ML, male legs; FSG, female sex glands; MSG, male sex glands. Error bars represent the standard error; those labeled with different letters are significantly different [p < 0.05, ANOVA, least-significant difference (LSD)].

FIGURE 3

Oviposition assay using three repellents for gravid females in O. furnacalis. The black bars indicate the preference of oviposition for each test chemical. The asterisks indicate a significant difference (**p < 0.01; ***p < 0.001).

FIGURE 4

Single sensillum recordings of s. trichoidea from female adults in O. furnacalis. Three different types (Type A–C) of s. trichoidea characterized by the response to nonanal, 1-octanol and octanal. The stimulus was applied for 300 ms which was represented with a red line under the trace.

FIGURE 5

Phylogenetic analysis for OfurOR27 and its homologous genes. Odorant receptors including PxylOR16, MsexOR12, MsepOR28, HassOR67, HarmOR67, CsupOR17, and CpomOR59 (Supplementary Dataset S1) were downloaded from the National Center for Biotechnology Information. All sequences were aligned using MAFFT software. The phylogenetic analysis was conducted by RAxML version 8. The final tree was visualized by FigTree version 1.4.0 software (http://tree.bio.ed.ac.uk/software/figtree/).

FIGURE 6

Alignment of the amino acid sequences of OfurOR27 and its homologous genes. The transmembrane domains of genes were predicted using TMHMM version 2.0 (http://www.cbs.dtu.dk/services/TMHMM/), and sequences were aligned using DNAMAN version 8 software (Lynnon LLC, San Ramon, CA, United States). Amino acids identical in all sequences were marked with black shading. Numbers to the left refer to the position of the last residue in a line in each odorant receptor (OR) sequence. The horizontal lines indicated the position of predicted transmembrane domains.