The role of horizontally transferred genes in the xenobiotic adaptations of the spider mite Tetranychus urticae

Plant feeding arthropods adapt in diverse ways to dietary plant toxins. The genetic basis of these adaptations is not well characterized, especially in non-insect lineages. Using the sequenced genome of the herbivorous spider mite Tetranychus urticae as a starting point, this work aimed at uncovering which genes and mechanisms underpin spider mite resistance to chemical plant defenses. First, the detoxification of the defensive compound produced by cyanogenic plants in spider mites was investigated. This work successfully identified the gene of which the protein product (B-cyanoalanine synthase) detoxifies plant synthesized cyanide and uncovered that this gene was horizontally transferred from a bacterial species. Second, genome-wide gene-expression responses upon various chemical pressures were further analyzed to explore the spider mite’s xenobiotic metabolism in more detail. New gene families, including one which was horizontally transferred from fungi (intradiol ring-cleaving dioxygenases), emerged as potential key components in the mite’s detoxification pathways. Additionally, these transcriptomic comparisons support the theorem that polyphagous herbivores co-opt their pre-evolved phytochemical detoxification pathways to detoxify synthetic pesticides.