Abstract
The recent outbreak of the mountain pine beetle (Dendroctonus ponderosae; MPB) has affected over 20 M hectares of pine forests in western North America. During the colonization of host trees, female MPB release the aggregation pheromone (−)-trans-verbenol. (−)-trans-Verbenol is thought to be produced from the pine defense compound (−)-α-pinene by cytochrome P450 (P450) dependent hydroxylation. MPB may also use P450s for the detoxification of other monoterpenes of the pine defense system. Here we describe the functional characterization of MPB CYP6DE1. CYP6DE1, but not the closely related CYP6DE2, used the bicyclic monoterpenes (−)-α-pinene, (+)-α-pinene, (−)-β-pinene, (+)-β-pinene and (+)-3-carene as substrates. CYP6DE1 was not active with other monoterpenes or diterpene resin acids that were tested as substrates. trans-Verbenol is the major product of CYP6DE1 activity with (−)-α-pinene or (+)-α-pinene as substrates. When tested with blends of different ratios of (−)-α-pinene and (+)-α-pinene, CYP6DE1 produced trans-verbenol with an enantiomeric profile that was similar to that produced by female MPB exposed to the α-pinene enantiomers.
Highlights
The mountain pine beetle (Dendroctonus ponderosae; MPB) is a pest of several pine (Pinus) species in western North America[1]
In a recent transcriptome screen of the MPB P450 gene family we identified P450s that are expressed in different body parts where monoterpene oxidation may occur, in antennae for olfaction, as well as in the alimentary canal and fat body for detoxification and pheromone formation[22]
MPB CYP6DE1 and CYP6DE2 were produced in Spodoptera frugiperda cells, isolated as microsomal membrane-bound proteins (Supporting Fig. S1), and identified as functional P450s based on carbon monoxide (CO)-spectra (Supporting Fig. S2)
Summary
The mountain pine beetle (Dendroctonus ponderosae; MPB) is a pest of several pine (Pinus) species in western North America[1]. It is conceivable that ancestors of MPB first evolved genes and enzymes for monoterpene detoxification as an essential process to survive conifer host defenses Such a detoxification resulted in the formation and release of monoterpenoid derivatives by beetles that may have been co-opted as pheromones. In a recent transcriptome screen of the MPB P450 gene family we identified P450s that are expressed in different body parts where monoterpene oxidation may occur, in antennae for olfaction, as well as in the alimentary canal and fat body for detoxification and pheromone formation[22]. Transcripts of CYP6DE3 (72% and 65% translated amino acid identity with CYP6DE1 and CYP6DE2, respectively) were more abundant in unfed males compared to fed males, unfed and fed females[21]
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