Discrete Roles of the Ir76b Ionotropic Co-Receptor Impact Olfaction, Blood Feeding, and Mating in the Malaria Vector Mosquito Anopheles coluzzii

Abstract

Anopheline mosquitoes rely on their highly sensitive chemosensory apparatus to detect diverse chemical stimuli that drive the host-seeking and blood-feeding behaviors required to vector pathogens for malaria and other diseases. This process incorporates a variety of chemosensory receptors and transduction pathways. We have used advanced in vivo gene-editing and -labelling approaches to localize and functionally characterize the ionotropic co-receptor AcIr76b in the malaria mosquito Anopheles coluzzii, where it impacts both olfactory and gustatory systems. AcIr76b has a broad expression pattern in female adult antennal grooved pegs, T1 and T2 sensilla on the labellum, stylets, and tarsi, as well as the larval sensory peg. AcIr76b is co-localized with the Orco odorant receptor (OR) co-receptor in a subset of cells across the female antennae and labella. In contrast to Orco and Ir8a, chemosensory co-receptors that appear essential for the activity of their respective sets of chemosensory neurons in mosquitoes, AcIr76b-/- mutants maintain wild-type peripheral responses to volatile amines on the adult palps, labellum, and the larval sensory cone. Interestingly, AcIr76b-/- mutants display significantly increased responses to amines in antennal grooved peg sensilla while coeloconic sensilla reveal significant deficits in responses to several acids and amines. Behaviorally, AcIr76b mutants manifest significantly female-specific insemination deficits and, although AcIr76b-/- mutant females are able to locate, alight, and probe artificial blood hosts, they are incapable of blood feeding successfully. Taken together, our study reveals a multi-dimensional functionality of Ir76b in Anopheline olfactory and gustatory pathways that directly impacts the vectorial capacity of these mosquitoes. SummaryChemosensory receptors play crucial roles across mosquito lifecycles where they often form functional complexes that require cognate co-receptors. To better understand mosquito chemosensory pathways in the malaria vector mosquito An. coluzzii we have utilized advanced gene editing approaches to localize and functionally characterize the ionotropic receptor co-receptor AcIr76b. Expression of AcIr76b was observed in antennal grooved pegs and other accessory olfactory appendages. Mutagenesis of AcIr76b uncovers both reduced and elevated neuronal responses to amines, which suggests a role in response modulation. In addition to olfactory phenotypes, AcIr76b mutants display significantly impaired mating and blood feeding capabilities. Our data reveals discrete roles of AcIr76b across olfactory and gustatory pathways and shed lights on the potential molecular target for vector control strategies.