UBC Theses and Dissertations
Detoxification of pine terpenoids by mountain pine beetle cytochromes P450 Chiu, Christine C.
The mountain pine beetle (Dendroctonus ponderosae; MPB) is an irruptive bark beetle species affecting pine forests of western North America. A recent outbreak has spread over more than 25 million hectares of pine forests now affecting pine species of sensitive boreal and mountain ecosystems. Pine hosts produce a viscous oleoresin comprised of terpenoids; monoterpene, sesquiterpenes and diterpene resin acids, as a defense against insects and other herbivores. The MPB is exposed to terpenoids for most of its life cycle and these compounds act as host defenses, kairomones, and as pheromone precursors. Cytochromes P450 (P450s) have been proposed to function in MPB detoxification of host defenses, olfaction, and pheromone biosynthesis. My research addressed the role of terpenoids as toxic host defenses and pheromone precursors, and the role of MPB P450s in the modification of terpenoids in detoxification, odorant degradation, and pheromone biosynthesis. In this thesis, I assessed the toxic effects of monoterpenes to MPB, and analyzed the terpenoid metabolic products formed by MPB and by MPB P450s from host monoterpenes and diterpene resin acids. I assessed the toxicity of ten monoterpenes to the MPB. This study helps to quantitatively define the effects of individual monoterpenes towards MPB mortality, which is critical when assessing the variable monoterpene chemical defense profiles of its host species. I identified a set of novel monoterpenyl esters in the MPB, including verbenyl ester and showed that these esters are accumulated by the female beetle early in the life cycle for future release of the MPB aggregation pheromone trans-verbenol. I investigated seven different MPB P450s, specifically CYP6DE1, CYP6DE2, CYP6DJ1, CYP6BW1, CYP6BW3, CYP9Z18 and CYP345E2, for their potential roles in detoxification, odorant degradation, and pheromone biosynthesis by quantifying the transcript abundance in the antennae and alimentary canal. I have characterized the biochemical functions of four of these MPB P450s. The results of my thesis provide new insights into MPB interactions with host terpenoids defenses and the roles of P450s in these interactions.
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