Identification and Expression Pattern Analysis of Cuticular Protein Gene Family in Monochamus alternatus (Coleoptera: Cerambycidae)

The pine sawyer beetle (Monochamus alternatus Hope, 1842) is a major vector of the pinewood nematode [Bursaphelenchus xylophilus (Steiner & Buhrer, 1934) Nickle, 1970]. A total of 119 cuticular protein (CP) genes were identified from the M. alternatus genome, belonging to nine families, namely 34 CPR-RR1, 39 CPR-RR2, 6 CPAP1, 7 CPAP3, 2 CPF, 3 CPFL, 4 CPCFC, 14 CPU, and 10 TWEEDLE, with the CPR family being the most abundant (73 genes, 61.34%). Comparative genomic analysis across six insect orders revealed that the CP gene count in M. alternatus (119) falls within the range observed among other Coleoptera species (119–173). Synteny analysis revealed seven tandem duplication events on chromosome 6 within the M. alternatus genome and 16 conserved syntenic gene pairs between M. alternatus and Tribolium castaneum (Herbst, 1797), distributed across six chromosomes. Expression profiling across larval, pupal, and adult stages revealed that CP genes within the same family exhibited distinct developmental-stage-specific expression patterns. Among the CPR-RR1 family, four genes (Malt029850.1, Malt047022.1, Malt029928.1, and Malt029871.1) showed higher expression levels; among the CPR-RR2 family, three genes (Malt014886.1, Malt031777.1, and Malt014882.1) showed higher expression. Quantitative real-time PCR validation confirmed that two CPR-RR1 genes (Malt029850.1 and Malt047022.1) were highly expressed in larvae, two CPR-RR1 genes (Malt029928.1 and Malt029871.1) were highly expressed in adults, and three CPR-RR2 genes (Malt014886.1, Malt031777.1, and Malt014882.1) were expressed predominantly in pupae.