Deorphanization of Cydia pomonella Or22 using a two-electrode voltage clamp

Insects use a variety of chemosensory proteins to detect and to respond to chemicals in their environments. Chemical cues dictate crucial behaviors such as host seeking, mate selection, and oviposition. Odorant receptors (ORs) are one family of transmembrane proteins that function as ligand-gated ion channels to specifically detect volatile compounds. Cydia pomonella (Lepidoptera: Tortricidae) is one of the most significant apple and pear pests worldwide. Understanding the chemical cues that lead this insect to host trees is crucial to controlling C. pomonella populations and reducing the damaging effects of infestations. Or22 of C. pomonella has been previously identified as a potentially important receptor for host seeking behavior. However, a more complete picture of Or22 sensitivities to different ligands is necessary to facilitate the development of novel attractant or repellents. In this study we used the two-electrode voltage clamp (TEVC) technique to measure Or22 responses to a novel panel of chemical ligands. Briefly, Or22 cRNA was coinjected into Xenopus laevis oocytes along with an obligate coreceptor, Aedes aegypti Orco, as a heterologous expression platform. Voltage changes were recorded in real time while a variety of chemical volatiles were perfused past oocytes in solution. We discovered that Or22 responds most robustly to the fruit odorant lactones delta-dodecalactone and gamma-undecalactone. Further work deorphanizing C. pomonella Ors and Or22 homologues will be required to elucidate the general principles of olfaction as well as specific chemosensory mechanisms in important pest species.