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

Abstract Background Drosophila suzukii is among the main pests of berries, and to which control, primarily through application of insecticides is challenging and urges alternative strategies. Methods based on targeting chemical sensing and interfering with the behavior of this pest insect are promising, and are facilitated by the isolation and functional characterization of chemosensory receptors aimed to identify 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. OR69a is well conserved within the genus Drosophila, and represents a candidate target for a broad behavioral interference based on chemosensory communication towards the design of novel control strategies. 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) with a panel of 48 ligands. We deorphanized these subunits to several compounds, including two possible kairomones (3-octanol and R-carvone) and (Z)-4-nonenal, a possible fly-emitted volatile compound, although with different pharmacological qualities. By coupling Gas Chromatography to Single Sensillum Recording (GC-SSR), we demonstrated these three ligands enhance ab3A-spiking at nanogram aliquots in a complementary fashion among the different OR69a variants, and we identified another possible kairomone, methyl salicylate, as the most active and specific ligand for the sole subunit DsuzOR69aB. In testing headspaces collected from D. suzukii female and from the fly-associated yeast Hanseniaspora uvarum by GC-SSR we did not observe 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 suggests kairomone specificity, even if effects may coexist for binding the possible fly-emitted volatile compound (Z)-4-nonenal in a complementary fashion. Among the possible kairomones, methyl salicylate is the most active ligand and it demonstrated to be specific to the sole DsuzOR69aB subunit, inspiring future investigation to validate potentials of this compound for D. suzukii pest control strategies.