Identification and Functional Characterization of the Leg-Enriched Chemosensory Protein PxylCSP9 in Plutella xylostella (Lepidoptera: Plutellidae)

<i>Plutella xylostella</i>, a major pest of cruciferous vegetables, depends predominantly on chemoreception to locate host plants. Legs are crucial in insect chemical perception, particularly during close-range and contact chemoreception. However, the molecular basis underlying the chemosensory repertoire in <i>P. xylostella</i> legs remains elusive. To address this, we sequenced chemosensory-related genes in diamondback moth legs. Sequencing identified 32 odorant binding protein (OBP), 18 chemosensory protein (CSP), 26 odorant receptor (OR), 20 gustatory receptor (GR), 15 ionotropic receptor (IR), and 3 sensory neuron membrane protein (SNMP) genes. Comparative analysis with antennal transcriptome data revealed three CSPs, seven ORs, and two GRs newly identified in the legs. Transcriptome analysis showed higher fragments per kilobase of transcript per million mapped reads values for CSPs than for other chemosensory-related gene families. Furthermore, qRT-PCR confirmed the highest expression of <i>PxylCSP9</i> in the legs, suggesting its role in perceiving external compounds. Fluorescent binding assays revealed high binding affinity of PxylCSP9 for several host plant semiochemicals. Molecular docking predicted a hydrophobic binding pocket in PxylCSP9 with Met11, Leu13, and Leu43 frequently participating in ligand interactions. Our findings indicate that leg-enriched PxylCSP9 is pivotal for host plant recognition during close-range chemoreception, suggesting its potential as a molecular target for precision management through behavior-based strategies.