Functional characterization of sensory neuron membrane protein 1a involved in sex pheromone detection of Apolygus lucorum (Hemiptera: Miridae)

The mirid bug Apolygus lucorum (Hemiptera: Miridae) is a polyphagous pest that affects a wide range of host plants. Its control remains challenging mainly due to its rapid reproduction, necessitating an understanding of sex pheromone communication. The recognition of sex pheromones is vital for courtship and mating behaviors, and is mediated by various chemosensory-associated proteins. Among these, sensory neuron membrane protein (SNMP), a CD36-related protein, is suggested to play crucial roles in detecting sex pheromones. In this study, we employed transcriptomic and genomic data from A. lucorum and phylogenetic approaches, and identified four putative SNMP genes (AlucSNMP1a, AlucSNMP1b, AlucSNMP2a, and AlucSNMP2b) with full open reading frames. Expression analysis revealed the ubiquitous presence of AlucSNMP transcripts in multiple tissues, with only AlucSNMP1a exhibiting male-biased expression in the antennae, suggesting its potential role in male chemosensation. Functional analysis using the Xenopus oocyte expression system, coupled with two-electrode voltage clamp recording, demonstrated that the co-expression of AlucSNMP1a with specific pheromone receptors (PRs) and the co-receptor (Orco) significantly enhanced electrophysiological responses to sex pheromones compared to the co-expression of PRs and Orco alone. Moreover, the results indicated that the presence of AlucSNMP1a not only affected the responsiveness to sex pheromones but also influenced the kinetics (activation and inactivation) of the induced signals. In contrast, the co-expression of AlucSNMP1b with AlucPR/Orco complexes had no impact on the inward currents induced by two pheromone compounds. An examination of the selective pressures on SNMP1 genes across 20 species indicated strong purifying selection, implying potential functional conservation in various insects. These findings highlight the crucial role of AlucSNMP1a in the response to sex pheromones.