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Detoxification of diterpene resin acids by the pine weevil (Hylobius abietis)


About This PhD Project

Project Description

Background: Many insect species feed on plants containing toxic defense compounds without any apparent negative effects. Since many such insects are important agricultural or forestry pests, scientists have been making intensive efforts to discover how insects can overcome chemical defenses. Bacterial symbionts in the insect gut have been suggested to help their hosts degrade plant defenses (Hammer and Bowers, 2015), and bacterial genes potentially involved in defense detoxification have been identified (Adams et al., 2013). However, little is known about how insect metabolize diterpenes, a major component of coniferous oleoresin. Diterpenes have been demonstrated to function as repellents, antifeedants or toxins to different species of insects and are reported to be degraded by both insects and bacteria, Martin et al., 1999, but no pathways or end products have been identified so far. The pine weevil (Hylobius abietis), a serious pest of conifer forests across Northern Europe, feeds reakily on the bark of newly planted seedlings without any obvious interference from the diterpene-containing oleoresin. Norway spruce, a common pine weevil host, contains different concentrations of diterpenes throughout its life cycle, and moderate amounts of diterpenes are not effective deterrents to weevil feeding. In fact, pine weevils have greater reproductive fitness when feeding on diets containing diterpenes. Therefore we hypothesize that H. abietis may be able to metabolize diterpenes in order to colonize their host plants successfully (Berasategui et al. 2017). On the other hand Norway spruce is able to induce higher levels of diterpene production, which may make seedlings unattractive again for the weevil depending on the biochemical properties of the detoxifying enzymes of the weevil and its bacteria.

Project Description: In this project, we propose to identify the diterpene detoxification strategies of the pine weevil with isotope labeling, biochemical and molecular approaches to determine the costs and benefits of detoxification from the insect’s perspective. We wish to determine the metabolic fates of diterpenes within insects, and then compare the degradation products of diterpene acids formed by insects and microbial gut-associates to find out whether these two detoxification processes are independent or complementary. Finally, identification of insect genes involved in diterpene degradation will allow manipulation of detoxification to determine its costs and benefits.

Candidate profile: We are looking for a highly motivated candidate with an MSc degree in biochemistry, chemistry, microbiology or a related field. Expertise in basic molecular biology and analytical chemistry are essential. He or she should be able to work independently. Excellent English skills (written and spoken) are required.

References

Adams AS, et al. Mountain Pine Beetles Colonizing Historical and Naïve Host Trees Are Associated with a Bacterial Community Highly Enriched in Genes Contributing to Terpene Metabolism. Applied and Environmental Microbiology: 2013, 79(11): 3468-3475.

Berasategui A, et al. Gut microbiota of the pine weevil degrades conifer diterpenes and increases insect fitness. Molecular Ecology: 2017, 26(15): 4099-4110.

Hammer TJ and Bowers MD. Gut microbes may facilitate insect herbivory of chemically defended plants. Oecologia: 2015, 179(1): 1-14.

Martin VJJ, et al. Recent advances in understanding resin acid biodegradation: microbial diversity and metabolism. Archives of Microbiology: 1999, 172(3): 131-138.

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