Mutagenesis of the odorant receptor co-receptor (Orco) reveals severe olfactory defects in the crop pest moth Helicoverpa armigera

Abstract

Background Odorant receptors (ORs) as odorant-gated ion channels play a crucial role in insect olfaction. They are formed by a heteromultimeric complex of the odorant receptor co-receptor (Orco) and a ligand-selective Or. Other types of olfactory receptor proteins, such as ionotropic receptors (IRs) and some gustatory receptors (GRs), are also involved in the olfactory system of insects. Orco as an obligatory subunit of ORs is highly conserved, providing an opportunity to systematically evaluate OR-dependent olfactory responses. Results Herein, we successfully established a homozygous mutant (Orco−/−) of Helicoverpa armigera, a notorious crop pest, using the CRISPR/Cas9 gene editing technique. We then compared the olfactory response characteristics of wild type (WT) and Orco−/− adults and larvae. Orco−/− males were infertile, while Orco−/− females were fertile. The lifespan of Orco−/− females was longer than that of WT females. The expressions of most Ors, Irs, and other olfaction-related genes in adult antennae of Orco−/− moths were not obviously affected, but some of them were up- or down-regulated. In addition, there was no change in the neuroanatomical phenotype of Orco−/− moths at the level of the antennal lobe (including the macroglomerular complex region of the male). Using EAG and SSR techniques, we discovered that electrophysiological responses of Orco−/− moths to sex pheromone components and many host plant odorants were absent. The upwind flight behaviors toward sex pheromones of Orco−/− males were severely reduced in a wind tunnel experiment. The oviposition selectivity of Orco−/− females to the host plant (green pepper) has completely disappeared, and the chemotaxis toward green pepper was also lost in Orco−/− larvae. Conclusions Our study indicates that OR-mediated olfaction is essential for pheromone communication, oviposition selection, and larval chemotaxis of H. armigera, suggesting a strategy in which mate searching and host-seeking behaviors of moth pests could be disrupted by inhibiting or silencing Orco expression.

RNAi verifications on olfactory defects of an essential biocontrol agent Agasicles hygrophila (Coleoptera: Chrysomelidae) regarding mating and host allocation

“…One is as Zhang et al (2019) discovered that both Orco pathway and IRs pathway are involved in acid sensing. Alternatively, as in Helicoverpa armigera, defects in Orco pathway do not alter the insect's response to acid (Fan et al, 2022). An interesting question for future research is whether Orco pathway is involved in acid sensing in A. hygrophila along with IRs pathway.…”

The larva and adult of Helicoverpa armigera use differential gustatory receptors to sense sucrose

“…The PER percentage of Gr6 −/− adults was not disappeared when the antennae and tarsi were stimulated by high fructose concentrations (Figure 7F and 7I ); this indicates that fructosetuned GRs other than Gr6 were involved. Previous studies have shown that Gr9 (Gr4 in Jiang et al, 2015 ), as an ortholog of DmelGr43a and BmorGr9, is a fructose-tuned GR (Ai et showed that Orco knockout had no significant effect on the expression of most OR, IR and GR genes in adult antennae of H. armigera although some genes were up-or down-regulated to a certain extent (Fan et al 2022 ). To elucidate the precise molecular mechanisms of sugar reception in H. armigera is necessary to compare a series of single, double and even multiple Gr knock-out lines and investigate the downstream effects of the GRs.…”

The olfactory system of Pieris brassicae caterpillars: from receptors to glomeruli

“…, 2019; Fan et al. , 2022). Chemoreceptors expressed in larvae are generally related to food sources.…”

“…It has the highest expression among all ORs in most cases and determines the olfactory sensitivity of insects. Insects lose most olfaction when Orco is knocked down or knocked out (Fandino et al, 2019;Fan et al, 2022). Chemoreceptors expressed in larvae are generally related to food sources.…”