Heterologous expression and functional characterization of Drosophila suzukii OR69a transcript variants unveiled response to kairomones and to a candidate pheromone

Authors: CATTANEO, ALBERTO - Swedish University Of Agricultural Sciences; WITZGALL, PETER - Swedish University Of Agricultural Sciences; KWADHA, CHARLES - Swedish University Of Agricultural Sciences; BECHER, PAUL - Swedish University Of Agricultural Sciences; Walker, William

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2022
Publication Date: 12/14/2022
Citation: Cattaneo, A.M., Witzgall, P., Kwadha, C., Becher, P.G., Walker III, W.B. 2022. Heterologous expression and functional characterization of Drosophila suzukii OR69a transcript variants unveiled response to kairomones and to a candidate pheromone. Journal of Pest Science. 96:1149-1171. https://doi.org/10.1007/s10340-022-01585-2.
DOI: https://doi.org/10.1007/s10340-022-01585-2

Interpretive Summary: The spotted wing drosophila (SWD) is a globally invasive insect pest to several fruit crops around the world. A better understanding of the basic biology of SWD could lead to novel ways to control this pest by disrupting host- or mate- finding behaviors. These behaviors in insects such as SWD are largely regulated by the sense of smell. Detection of odors from the environment result in activation of behavioral responses. Odorant detection is primarily mediated by a family of proteins known as odorant receptors. Researchers at the USDA-ARS in Wapato, WA and at the Swedish University of Agricultural Sciences studied the function of three odorant receptors identified from SWD. They discovered that SWD uses these receptors to food, and perhaps to communicate using pheromones. Some of the odorants that were discovered to activate these receptors were also not previously known to be important to SWD behavior. These results will allow the researchers to find ways to block these receptors and influence or manipulate SWD behavior in the orchards as a novel way to control SWD.

Technical Abstract: Drosophila suzukii is among the main pests threatening berry production with a host preference for ripened fruit, making application of insecticides challenging, urging the need for alternative control strategies. Methods based on targeting chemical sensing and interfering with the behavior of this pest insect are promising, opening to the isolation and the functional characterization of its chemosensory receptors aimed to identify novel behaviorally active ligands. In our previous investigations we functionally characterized subunits of the OR69a locus of Drosophila melanogaster as being capable to bind both pheromones and kairomones, representing possible candidates within the genus Drosophila for a broad behavioral interference to the design of novel control strategies based on chemosensory communication. Results: By means of heterologous expression in empty ab3A neurons of D. melanogaster together with Single Sensillum Recording (SSR), we screened three OR69a-subunits we have identified in D. suzukii (DsuzOR69aA, DsuzOR69aB, DsuzOR69aC) to a panel of 48 ligands. We deorphanized these subunits to several compounds, including two possible kairomones (3-octanol and R-carvone) and one possible pheromone [(Z)-4-nonenal] capable to bind OR69as, although with different pharmacology. By coupling Gas Chromatography to Single Sensillum Recording (GC-SSR), we demonstrated these ligands enhancing ab3A-spiking at nanogram aliquots in a complementary fashion, and we identified another possible kairomone, methyl salicylate, as the most active and specific ligand for the sole subunit DsuzOR69aB. By testing headspaces collected from D. suzukii female and from the yeast Hanseniaspora uvarum by GC-SSR we demonstrated absence of activation from female headspaces but activation from headspaces collected from yeast. In situ hybridization analysis conducted on D. suzukii antennae suggested unique expression of OR69a-subunits into specific neurons as well as their possible co-expression within the same neurons. Conclusions: The OR69a-subunits of D.suzukii constitute cation channels which binding seem to be specific to kairomones, even if effects coexist for binding the possible pheromone (Z)-4-nonenal in a complementary fashion. Among the kairomones, methyl salicylate is the most active ligand and it demonstrated to be specific to the sole DsuzOR69aB subunit, opening validation of its potentials for D. suzukii pest control strategies.