Access to the odor world: olfactory receptors and their role for signal transduction in insects

Abstract

The sense of smell enables insects to recognize and discriminate a broad range of volatile chemicals in their environment originating from prey, host plants and conspecifics. These olfactory cues are received by olfactory sensory neurons (OSNs) that relay information about food sources, oviposition sites and mates to the brain and thus elicit distinct odor-evoked behaviors. Research over the last decades has greatly advanced our knowledge concerning the molecular basis underlying the reception of odorous compounds and the mechanisms of signal transduction in OSNs. The emerging picture clearly indicates that OSNs of insects recognize odorants and pheromones by means of ligand-binding membrane proteins encoded by large and diverse families of receptor genes. In contrast, the mechanisms of the chemo-electrical transduction process are not fully understood; the present status suggests a contribution of ionotropic as well as metabotropic mechanisms. In this review, we will summarize current knowledge on the peripheral mechanisms of odor sensing in insects focusing on olfactory receptors and their specific role in the recognition and transduction of odorant and pheromone signals by OSNs.

The diversity and evolution of odorant receptors in beetles (Coleoptera)

“…The behaviour and ecology of insects can often be framed in terms of their olfactory biology, which mediates such diverse activities as host‐seeking, mating, communication, and avoidance behaviours (Wyatt, ; Gadenne et al ., ). Complex olfactory information is encoded by a large and divergent repertoire of chemoreceptor proteins, which includes three primary families of receptors (Fleischer et al ., ): the gustatory receptors (GRs), ionotropic receptors (IRs) and odorant receptors (ORs). GRs detect nonvolatile chemicals and contribute to the detection of carbon dioxide (Jones et al ., ; Robertson and Kent, ), whereas the olfactory antennal IRs are associated with the detection of mainly acids and amines (Ai et al ., ; Min et al ., ).…”

A subset of chemosensory genes differs between two populations of a specialized leaf beetle after host plant shift

“…In smell and taste, the receptor proteins of peripheral neurons play a pivotal role as biological transducers that convert external chemical signals into a sensory input. These receptors operate as ligand-gated ion channels and a potential modulatory role for G proteins, and second messenger downstream of the receptor is suggested (Fleischer, Pregitzer, Breer, & Krieger, 2017;Sato, Tanaka, & Touhara, 2011;Sato et al, 2008;Wicher et al, 2008;Zhang et al, 2011).…”

The Two Main Olfactory Receptor Families in Drosophila, ORs and IRs: A Comparative Approach

“…Despite the recent increase in knowledge about the main receptor families in olfaction in Drosophila (see reviews by Wilson, 2013; Carraher et al, 2015; Joseph and Carlson, 2015; Fleischer et al, 2018; Rimal and Lee, 2018), there are still many open questions that remain to be answered.…”

“…Furthermore, in both types of organisms, each OSN expresses one or very few olfactory molecular receptors, and the axons of OSNs that express the same receptor project to the same glomeruli in both the olfactory bulb and the antennal lobe (Su et al, 2009). These similarities and the fact that Drosophila is a widespread model organism in genetics and neurobiological research made its olfactory system an attractive and simple model to study olfaction (see, for example, the recent reviews by Wilson, 2013; Barish and Volkan, 2015; Carraher et al, 2015; Joseph and Carlson, 2015; Fleischer et al, 2018; Grabe and Sachse, 2018; Rimal and Lee, 2018). …”