Abstract
BackgroundThe mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) is a highly destructive pest of pine forests in western North America. During flight to a new host tree and initiation of feeding, mountain pine beetles release aggregation pheromones. The biosynthetic pathways of these pheromones are sex-specific and localized in the midgut and fat body, but the enzymes involved have not all been identified or characterized.ResultsWe used a comparative RNA-Seq analysis between fed and unfed male and female MPB midguts and fat bodies to identify candidate genes involved in pheromone biosynthesis. The 13,407 potentially unique transcripts showed clear separation based on feeding state and gender. Gene co-expression network construction and examination using petal identified gene groups that were tightly connected. This, as well as other co-expression and gene ontology analyses, identified all four known pheromone biosynthetic genes, confirmed the tentative identification of four others from a previous study, and suggested nine novel candidates. One cytochrome P450 monooxygenase, CYP6DE3, identified as a possible exo-brevicomin-biosynthetic enzyme in this study, was functionally characterized and likely is involved in resin detoxification rather than pheromone biosynthesis.ConclusionsOur analysis supported previously characterized pheromone-biosynthetic genes involved in exo-brevicomin and frontalin biosynthesis and identified a number of candidate cytochrome P450 monooxygenases and a putative cyclase for further studies. Functional analyses of CYP6DE3 suggest its role in resin detoxification and underscore the limitation of using high-throughput data to tentatively identify candidate genes. Further functional analyses of candidate genes found in this study should lead to the full characterization of MPB pheromone biosynthetic pathways and the identification of molecular targets for possible pest management strategies.
Highlights
The mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) is a highly destructive pest of pine forests in western North America
RNA sequencing (RNA-Seq) quality control and validation A total of 424,776,657 paired-end reads consisting of at least 76 bp were recovered from the 16 libraries, with reads per library ranging from 18,659,429 to 33,943,439 with a mean of 26,548,541
For the 15 genes in the seven samples measured by qRTPCR and RNA-Seq, Pearson and Spearman Correlation Coefficients averaged to 0.924 and 0.878, respectively (Table 2)
Summary
The mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) is a highly destructive pest of pine forests in western North America. During flight to a new host tree and initiation of feeding, mountain pine beetles release aggregation pheromones. The biosynthetic pathways of these pheromones are sex-specific and localized in the midgut and fat body, but the enzymes involved have not all been identified or characterized. The mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) uses three main pheromone components to coordinate the “mass attack” necessary to overcome a host tree’s defenses. Each component has a distinctive role and is produced from a different metabolic pathway (Fig. 1). Females produce the aggregation pheromone (–)-trans-verbenol [(1S,2R,5S)4,6,6-trimethylbicyclo[3.1.1] hept-3-en-2-ol], to attract. Nadeau et al BMC Genomics (2017) 18:311 A P450
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