Identifying pheromone biosynthetic genes in Neoclytus m. mucronatus (Coleoptera: Cerambycidae) using a differential gene expression approach

The longhorned beetles (Coleoptera: Cerambycidae) are among the most economically important pests of natural and managed forest systems worldwide. Many species produce volatile pheromones to unite the sexes on an appropriate host, and display a characteristic posture while releasing pheromone, or “calling.” Pheromones have been identified for several species and are used in monitoring efforts, but little is known about the biosynthesis of cerambycid pheromones. In this study, we used a differential gene expression approach to identify genes that may be involved in pheromone production. Total RNA was extracted from male Neoclytus m. mucronatus that were either 1) dormant in the morning before dawn, 2) actively calling at noon and 3) actively feeding beetles that were not calling at noon (n=3 for each group). We test the hypothesis that transcripts from pheromone biosynthetic genes are expressed at higher levels in beetles actively releasing pheromone than in resting beetles. A total RNA library was constructed from the extracts using RNAseq, and the relative expression levels between each treatment were compared using the edgeR and DESeq2 packages in R/Bioconductor. We found 50 contigs that were more highly expressed in the noon group, and 48 that were more highly expressed in the morning group. Among the differentially expressed contigs were a short-chain dehydrogenase/reductase resembling a pheromone biosynthetic gene found in Musca domestica, and a cytochrome P450 that closely resembles CYP18A1 in Tribolium castaneum. Understanding genes and key enzymes in the biosynthetic pathway may open new avenues for controlling these pests. This project will also add valuable information about the coding regions from the genome in this group of beetles for which very little is known.