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The unique dioxygenases of phytophagous spider mites: new enzyme players in plant-herbivore interactions?

Periodic Reporting for period 1 - DOGMITE (The unique dioxygenases of phytophagous spider mites: new enzyme players in plant-herbivore interactions?)

Reporting period: 2015-09-01 to 2017-08-31

Detoxification of poisonous xenobiotics in animals is typically performed by multi-gene enzyme families. Within arthropods, only insect genomes have been studied in detail where these detoxification families are well characterized. We recently uncovered a new enzyme family in the genome of a non-insect arthropod, the extremely polyphagous plant-feeding spider mite Tetranychus urticae. Phylogenetic analysis showed that this proliferated family was acquired through horizontal gene transfer from a fungal donor. The fungal homologues are known to code for secreted intradiol ring-cleavage dioxygenases that cleave a particular set of complex aromatic structures, commonly found in pesticides and toxic plant metabolites. It is our hypothesis that the acquisition and proliferation of this novel family in plant-feeding spider mites provides a selective advantage by detoxifying both natural and synthetic xenobiotics. This newly discovered genetic repertoire of spider mites is of huge interest for the bioremediation of man-made aromatic environmental pollutants such as PCBs and pesticides. By means of this multi-disciplinary project, we aim to study its precise role in mite (xenobiotic) metabolism and expect to open up avenues to new and exciting biotechnological applications that will extend well beyond agriculture.
In a first set of experiments, we quantified and timed the transcriptional responses of five dioxygenase genes to different plants and artificial diets. These experiments significantly advanced our knowledge of which specific toxic plant metabolites and nutritive factors induce dioxygenase gene-expression in spider mites. The role of the laterally acquired dioxygenases in mite physiology was further investigated by functionally expressing five intradiol ring-cleavage dioxygenase genes in a range of biological systems. These were: E. coli, insect cells (Sf9 and Hi5), Arabidopsis (Agrobacterium-mediated flower dipping) and Drosophila melanogaster (UAS-GAL4). Cutting-edge differential metabolomics will now identify the substrates and reaction products.
As the dioygenase genes seem to be associated with the xenobiotic metabolism of mite pests, pest management strategies benefit from the elucidation of their precise biological role. In addition, this project gives more insight into how horizontal gene transfer shapes eukaryotic evolution and is of interest within the broader societal debate of genetic modification.