An odorant receptor from Anopheles gambiae that demonstrates enantioselectivity to the plant volatile, linalool

Abstract

Insects express chemical receptors within sensory neurons that are activated by specific cues in the environment, thereby influencing the acquisition of critical resources. A significant gap in our current understanding of insect chemical ecology is defining the molecular mechanisms that underlie sensitivity to plant-emitted volatiles. Linalool is a commonly-occurring monoterpene that has various effects on insect behavior, either acting as an attractant or a repellent, and existing in nature as one of two possible stereoisomers, (R)-(–)-linalool and (S)-(+)-linalool. In this study, we have used a cell-based functional assay to identify linalool and structurally-related compounds as ligands of Odorant receptor 29, a labellum-expressed receptor in the malaria vector mosquito, Anopheles gambiae (AgamOr29). While (R)-(–)-linalool activates AgamOr29, a mixture of the (R) and (S) stereoisomers activates the receptor with higher potency, implying enantiomeric selectivity. Orthologs of Or29 are present in the genomes of Anophelines within the Cellia subgenus. The conservation of this receptor across Anopheline lineages suggests that this ecologically important compound might serve as an attraction cue for nectar-seeking mosquitoes. Moreover, the characterization of a mosquito terpene receptor could serve as a foundation for future ligand-receptor studies of plant volatiles and for the discovery of compounds that can be integrated into push-pull vector control strategies.

Metabolomics as an Emerging Tool for the Study of Plant–Pathogen Interactions

“…Maize plants exposed to molasses grass (Melinis minutiflora) for a period of three weeks showed decreased egg deposition by stemborers (Chilo partellus) compared to maize kept in isolation [103]. Interestingly, this research group found that VOCs from the molasses grass-exposed plants contained elevated levels of compounds such as (R)-linalool, a molecule known to influence insect behavior [103,104]. In another study on switchgrass, feeding by fall armyworms (Spodoptera frugiperda) induced significant production of monoterpenes and sesquiterpenes-at 17% and 26% of the total VOC composition, respectively-which are compounds known to have defense activity against herbivory [157,158].…”

Culex quinquefasciatus larvae development arrested when fed on Neochloris aquatica

“…These compounds have effects on reproduction, survival and in inhibiting the growth of competitive species, and maybe this is the reason why the initial culture, in the mosquito breeding site, was almost a monoalgal culture. On the other hand, microalgae produce volatiles compounds that might act as attractants for some insects, including mosquitoes, such as fatty acids derivatives [44,45], terpenoids [46], alcohols [47], and aldehydes [48]. Mosquitoes depend on olfactory signals to carry out behavioral activities, such as locating preys or hosts, selecting places to lay their eggs, courtship, and others, that they detect through their sensory organs.…”

Olfactory systems across mosquito species

“…For instance, cells expressing AgOR29 in Anopheles gambiae show a larger response to a mixture of (R)-(−)-and (S)-( +)-linalool compared with (R)-(−)-linalool alone. This suggests that AgOR29 is more sensitive to (S)-(+)-linalool than to (R)-(−)-linalool (Huff and Pitts 2019). In contrast, AaOR8 of Aedes aegypti is more sensitive to (R)-1-octen-3-ol than to (S)-1-octen-3-ol (Bohbot and Dickens 2009), which translates to a larger neuronal response to (R)-1-octen-3-ol than to (S)-1-octen-3-ol as well as a behavioural preference (Cook et al 2011).…”

“…Some mosquito ORs show enantio-selectivity, which means that they have different affinities to the two forms, R and S, of a chiral molecule (Bohbot and Dickens 2009;Cook et al 2011;Dekel et al 2016;Huff and Pitts, 2019). For instance, cells expressing AgOR29 in Anopheles gambiae show a larger response to a mixture of (R)-(−)-and (S)-( +)-linalool compared with (R)-(−)-linalool alone.…”