Chemosensory System Decoding: Transcriptome-Wide Identification and Expression Profiling of Olfactory Genes in Lytta sifanica.

The insect olfactory system relies on a sophisticated repertoire of olfactory-related proteins to enable precise odor detection and subsequent signal transduction. Their expression and regulation are crucial for mediating communication between themselves and environments. Lytta sifanica (Coleoptera: Meloidae), a species of significant economic importance, represents a notable subject for olfactory studies, particularly as it is renowned for producing the medically relevant toxin cantharidin. However, the molecular basis of olfactory sensation in the Blister Beetle Lytta sifanica has not yet been characterized. In this study, the transcriptomes of adult L. sifanica antennae were sequenced and analyzed. A total of 70 chemosensory genes, including 17 odorant binding proteins (OBPs), 5 chemosensory proteins (CSPs), 13 gustatory receptors (GRs), 17 odorant receptors (ORs), 13 ionotropic receptors (IRs) and 5 sensory neuron membrane proteins (SNMPs) were identified based on sequence homology analysis and phylogenetic reconstruction. The expression profiles of all candidate genes were confirmed by RT-PCR across multiple tissues, including antennae, head, mouthparts, pronotum, foreleg tarsus, abdomen skin, and wings. The results revealed that olfactory-related protein families were broadly expressed in the tested tissues, though with distinct tissue-specific patterns among different gene families. Among the identified chemosensory genes, eleven members are predominantly expressed in the antennae (Lsif_OBP1/2/19d, Lsif_OR2/20/49b, Lsif_IR2a, Lsif_GR7/127, Lsif_CSP1, and Lsif_SNMP2/4). In contrast, twenty-two members were exclusively expressed in the mouthparts (Lsif_OBP70/56d2, Lsif_GR12a/21/28a/68a), foreleg tarsus (Lsif_OR6/67c, Lsif_GR12, and Lsif_OBP2) and were abundant in the non-olfactory tissues head (Lsif_OBP99a, Lsif_OR9a/49b, Lsif_IR25a/56e, and Lsif_CSP6), pronotum (Lsif_OBP5/C20, Lsif_ORco, Lsif_OR13, and Lsif_IR7), abdomen skin (Lsif_SNMP5), suggesting their various functions in the olfactory system of L. sifanica. This research offers an extensive resource for investigating the chemoreception mechanism in beetle L. sifanica.