Intradiol ring cleavage dioxygenases from herbivorous spider mites as a new detoxification enzyme family in animals

Abstract

Background Generalist herbivores such as the two-spotted spider mite Tetranychus urticae thrive on a wide variety of plants and can rapidly adapt to novel hosts. What traits enable polyphagous herbivores to cope with the diversity of secondary metabolites in their variable plant diet is unclear. Genome sequencing of T. urticae revealed the presence of 17 genes that code for secreted proteins with strong homology to “intradiol ring cleavage dioxygenases (DOGs)” from bacteria and fungi, and phylogenetic analyses show that they have been acquired by horizontal gene transfer from fungi. In bacteria and fungi, DOGs have been well characterized and cleave aromatic rings in catecholic compounds between adjacent hydroxyl groups. Such compounds are found in high amounts in solanaceous plants like tomato, where they protect against herbivory. To better understand the role of this gene family in spider mites, we used a multi-disciplinary approach to functionally characterize the various T. urticae DOG genes. Results We confirmed that DOG genes were present in the T. urticae genome and performed a phylogenetic reconstruction using transcriptomic and genomic data to advance our understanding of the evolutionary history of spider mite DOG genes. We found that DOG expression differed between mites from different plant hosts and was induced in response to jasmonic acid defense signaling. In consonance with a presumed role in detoxification, expression was localized in the mite’s gut region. Silencing selected DOGs expression by dsRNA injection reduced the mites’ survival rate on tomato, further supporting a role in mitigating the plant defense response. Recombinant purified DOGs displayed a broad substrate promiscuity, cleaving a surprisingly wide array of aromatic plant metabolites, greatly exceeding the metabolic capacity of previously characterized microbial DOGs. Conclusion Our findings suggest that the laterally acquired spider mite DOGs function as detoxification enzymes in the gut, disarming plant metabolites before they reach toxic levels. We provide experimental evidence to support the hypothesis that this proliferated gene family in T. urticae is causally linked to its ability to feed on an extremely wide range of host plants.

Trans-driven variation in expression is common among detoxification genes in the extreme generalist herbivore Tetranychus urticae

“…Further, albeit with less precision in space, time, or nature of the selective agent(s), adaptation of herbivores to their host plants has also provided well-known examples of evolution in action [24,25]. Finally, a number of gene families have been associated with the detoxification, sequestration, or transport and excretion of pesticides, and are either known or are likely to be critical in host plant adaptation as well (i.e., to overcome toxic plant-produced specialized compounds, although plants deploy other defense strategies as well) [24][25][26][27][28][29][30][31][32]. Therefore, many selective agents are known for adaptation in herbivores, sometimes exactly (pesticides), as are genes and gene families that are strong candidates to underlie rapid phenotypic evolution.…”

Abundant trans-driven variation in detoxification gene expression in the extreme generalist herbivore Tetranychus urticae

“…At the family level, this was especially striking for DOG s, for which the near family-wide upregulation in MAR-ABi compared to SOL-BEi was under trans -control with only minor contributions from cis effects. Recently, several T. urticae DOGs including DOG11 were shown to have broad substrate specificity against aromatic compounds, including plant-derived specialized compounds with roles in plant defense against herbivores [41]. DOG11 was the most highly over-expressed DOG gene in both MAR-ABi and MR-VPi, both of which had comparatively high performance on tomato.…”

“…DOG11 was the most highly over-expressed DOG gene in both MAR-ABi and MR-VPi, both of which had comparatively high performance on tomato. RNAi knockdown of DOG11 in the MR-VPi progenitor strain was recently found to reduce performance on tomato [41], and whether trans -mediated upregulation of DOG11 contributes to the relatively high fitness of these strains on tomato warrants further study. Apart from CYPs and DOGs, it was also striking that specific genes in most other detoxification families, and some associated with host plant use (host use or peptidase gene sets), were also among those with the highest differential expression arising from trans control.…”

“…Further, albeit with less precision in space, time, or nature of the selective agent(s), adaptation of herbivores to their host plants has also provided well-known examples of evolution in action [30][31][32][33][34]. Finally, a number of gene families have been associated with the detoxification, sequestration, or transport and excretion of pesticides, and are either known or are likely to be critical in plant host adaptation as well (i.e., to overcome toxic plant-produced specialized compounds, although plants deploy other defense strategies as well) [33][34][35][36][37][38][39][40][41]. Therefore, many selective agents are known for adaptation in herbivores, sometimes exactly (pesticides), as are genes and gene families that are strong candidates to underlie rapid phenotypic evolution.…”

“…In addition, it acquired several putative detoxification genes by horizontal gene transfer that subsequently proliferated in the genome [43]. These include intradiol-ring cleavage dioxygenases (DOGs) that have recently been shown to cleave an unexpectedly wide range of aromatic plant defense specialized compounds [41], as well as bacterial UDP- glucuronosyltransferases (UGTs) [44], demonstrating the adaptive advantage of horizontal gene transfer in the context of detoxification and host plant use [42,43,45]. Gene-expression studies have revealed large and similar transcriptomic differences in these gene families between acaricide susceptible and resistant T. urticae strains, as well as after adaptation to new host plants [33,34,46], suggesting a link between host plant use and acaricide resistance.…”