Molecular Basis of Xenobiotic Metabolism and Resistance in Tetranychus urticae

This dissertation addresses the molecular basis of xenobiotic metabolism and chemical resistance in the two-spotted spider mite, Tetranychus urticae (TSSM). TSSM is an exceptionally polyphagous agricultural pest that attacks more than 1,100 plant species and is a significant cause of crop loss worldwide. The global impact of this single pest, driven in part by its rapid reproduction and capacity to evolve resistance to acaricides, has been estimated at approximately $1.6 billion in losses annually. Confronting this economic and agronomic threat requires new strategies for control, and this research focuses on identifying and characterizing specific mite proteins that underpin detoxification and resistance mechanisms, with the goal of informing rational acaricide design.

The project systematically characterizes four classes of TSSM enzymes implicated in xenobiotic metabolism: intradiol ring-cleavage dioxygenases, a glutathione S-transferase (GST), a β-cyanoalanine synthase, and uridine diphosphate glycosyltransferases (UGTs). Each enzyme class contributes to the mite’s capacity to neutralize or eliminate toxic compounds encountered in its environment, whether plant-produced xenobiotics or synthetic acaricides. Intradiol ring-cleavage dioxygenases participate in the breakdown of toxic aromatic compounds, facilitating their metabolic processing. GSTs conjugate reduced glutathione to diverse xenobiotics, a canonical detoxification route often associated with insecticide resistance. The β-cyanoalanine synthase contributes to detoxification of cyanide; functional silencing of this gene in TSSM reduces mite survival on cyanogenic plants, indicating its ecological and defensive importance. UGTs catalyze glycosylation of xenobiotics, attaching sugar moieties via UDP-sugar donors to increase solubility and promote excretion; these enzymes have been implicated in detoxifying acaricides such as abamectin.

A central emphasis of the research is not merely cataloging enzyme activities but revealing structural and functional details, particularly via crystallographic characterization, that expose unique properties of these proteins. By solving crystal structures and combining structural insight with functional assays, the work aims to identify active-site features, substrate interactions, and mechanistic vulnerabilities that could be exploited in the design of new acaricides selective for mite targets. Such targeted design could overcome broad-spectrum resistance mechanisms and reduce non-target impacts by focusing on mite-specific structural motifs or catalytic mechanisms.

Through the combined structural biology and biochemical characterization of these detoxification enzymes, Chruszcz’s research frames potential protein targets for novel control measures against TSSM. The approach integrates fundamental enzymology with applied goals: understanding how TSSM processes xenobiotics at the molecular level can drive the development of inhibitors or novel chemistries that evade existing resistance. Ultimately, this work contributes a molecular roadmap for designing acaricides that are more effective against resistant TSSM populations and supports long-term strategies to mitigate agricultural losses caused by this pervasive pest.