Odorant Receptor PxylOR11 Mediates Repellency of Plutella xylostella to Aromatic Volatiles

Abstract

Insects can use plant volatiles to guide certain behaviors, such as courtship, mating, host positioning, and habitat selection. Plutella xylostella is a global agricultural pest and has always been closely studied, but relatively few studies assess the molecular mechanism of P. xylostella exposed to plant volatiles. In this study, we analyzed the role of the odorant receptor PxylOR11 when P. xylostella is exposed to plant volatiles. Our analysis of tissue expression demonstrated that PxylOR11 is expressed in the antennae and that expression levels in female moths were significantly higher than in male moths. Functional analyses using the Xenopus oocyte expression system demonstrated that PxylOR11 was tuned to three aromatic compounds: benzyl alcohol, salicylaldehyde, and phenylacetaldehyde. Electroantennogram analyses revealed that these three aromatic compounds can induce electrophysiological responses in the antennae of P. xylostella, and that the electroantennograms response value of female moths was significantly higher than that of male moths. Dual-choice bioassays demonstrated that the three aromatic compounds have a repellent effect on female P. xylostella. These results suggest that PxylOR11 has a role in mediating the repellent effect of aromatic volatiles on P. xylostella and can be used as a potential target to design novel olfactory regulators controlling P. xylostella.

Keywords: Plutella xylostella; behavioral response; odorant receptor; repellent; two-electrode voltage clamp recordings.

FIGURE 1

Amino acid alignment of PxylOR11 homologous genes. Pxyl, P. xylostella; Harm, H. armigera; Bmor, B. mori. The seven transmembrane domains (TM1-TM7) are marked with red lines at the top.

FIGURE 2

Phylogenetic analysis of PxylOR11 with candidate ORs from Lepidoptera. Pxyl, P. xylostella (red); Harm, H. armigera (blue); Hvir, H. virescens (green); Bmor, B. mori (purple). The clade in green indicates the Orco co-receptor gene clade and the one in blue is the PRs gene clade. The PxylOR11 is indicated with the red star.

FIGURE 3

Expression profiles of PxylOR11 in different tissues of female and male P. xylostella. A, antennae; H, heads; T, thoraxes; Ab, abdomens; L, legs; G, genitalia. The one asterisks indicate significant differences between males and females (t-Test, p < 0.05). Error bars indicate the SEM (n = 3).

FIGURE 4

Responses of P. xylostella OR11/Orco to plant volatile compounds by in vitro functional scanning. (A) Inward current responses of PxylOR11/PxylOrco Xenopus oocytes exposed to compounds. (B) Buffer-injected Xenopus oocytes failed to respond to any of the compounds. (C) The structures of three aromatic compounds benzyl alcohol, salicylaldehyde, and phenylacetaldehyde are shown. (D) Response profile of PxylOR11/PxylOrco Xenopus oocytes. Error bar indicate SEM (n = 6).

FIGURE 5

Electrophysiological responses measured as electroantennograms (EAG) of female and male P. xylostella antennae to three ligands (benzyl alcohol, salicylaldehyde, and phenylacetaldehyde) of PxylOR11. Error bars indicate SEM (n = 10). Asterisks indicate the significant differences between females and males. *, p < 0.05; **, p < 0.01; ***, p < 0.001.

FIGURE 6

Behavioral responses of female and male P. xylostella to benzyl alcohol (A), salicylaldehyde (B), and phenylacetaldehyde (C). Each bar shows % of P. xylostella that chose either of the odor sources. Numbers in bars are the total numbers of P. xylostella choosing that odor sources. Choices between odor sources were analyzed with χ² goodness-of-fit tests on numbers (NS, no significant difference, p > 0.05; ***p < 0.001; **, p < 0.01; *, p < 0.05).