SNMP1 Contributes to Sensitive Pheromone and Plant Volatile Detection in the Locust Olfactory System

In holometabolous insects, such as flies and moths, the sensory neuron membrane protein 1 (SNMP1) has been primarily linked to the olfactory detection of long-chain aliphatic pheromones, but whether it plays an important role in receiving other chemical cues is largely unknown. Here, comparing electroantennogram (EAG) recordings of wild-type (WT) and SNMP1-deficient (SNMP1^-/-) hemimetabolous desert locusts (Schistocerca gregaria), we found that mutant animals showed significantly reduced responses to several pheromones and plant odorants belonging to different classes of aromatic and aliphatic substances. Our findings show that SNMP1 contributes more broadly to the detection of various chemicals, such as benzenoids, aliphatic aldehydes, and non-aromatic cyclic substances. Importantly, the decrease in antennal reactivity of SNMP1 mutants to certain chemicals was higher at lower concentrations of these substances, suggesting the relevance of SNMP1 for the sensitivity of olfactory detection. Moreover, behavioral experiments with WT and SNMP1^-/- animals showed that SNMP1 is crucial for the attraction of desert locusts by food plant scents. To examine whether diminished olfactory responses in SNMP1^-/- animals were due to reduced expression of odorant receptors (ORs), transcriptional levels of selected OR types were scrutinized by quantitative PCR (qPCR). In these approaches, no significant reduction in the expression of the ORs was found in SNMP1^-/- locusts, suggesting that the compromised responsiveness to certain substances is presumably not based on impaired receptor expression. Overall, our findings reveal that SNMP1 is critical for olfactory sensitivity in locusts and expand the current view of SNMP1 from a protein particularly essential for receiving aliphatic pheromones to a more general olfactory element important for proper sensing of a broader range of chemical cues, including plant odorants.