Rapid specialization of counter defenses enables two-spotted spider mite to adapt to novel plant hosts

Abstract

Classification: Biological Sciences, Evolutionary Biology 1 2The generalist herbivore Tetranychus urticae (Koch) adapts to novel plant hosts through rapid 3 evolution of metabolic resistance 4 5Abstract 20Genetic adaptation, occurring over long evolutionary time, enables host-specialized herbivores 21to develop novel resistance traits and to counteract the defenses of a narrow range of host 22plants. In contrast, physiological acclimation, leading to the suppression and/or detoxification of 23 host defenses is hypothesized to enable generalists to shift between plant hosts. Here, we 24 examined the long-term response of an extreme generalist, the two-spotted spider mite, 25Tetranychus urticae Koch (TSSM), to the shift to the non-preferred and novel host plant 26Arabidopsis thaliana. We identified the key requirement of two tiers of cytochrome P450 27 monooxygenases for TSSM adaptation to Arabidopsis: general xenobiotic-responsive P450s that 28 have a limited contribution to mite adaptation to Arabidopsis and adaptation-associated P450s 29 that efficiently counteract Arabidopsis defenses, illustrating that in about 25 generations of 30 TSSM selection on Arabidopsis plants mites evolved metabolic resistances characteristic of both 31 generalist and specialist herbivores. 32 33

Short term transcriptional responses of P450s to phytochemicals in insects and mites

“…CYP6AE, CYP321 and more Clan 3, Clan 4 P450s / [ 25 ] Spodoptera frugiperda (Lepidoptera) P Corn, Rice RNA-seq (Illumina HiSeq 2500) e.g. CYP6(AB4, AE9) 3 , CYP332A1 3 , CYP4(L6, M5) 4 / [ 77 ] Tetranychus cinnabarinus (Trombidiformes) P Cowpea, Cotton RNA-seq (Illumina HiSeq 2000) RT-qPCR a CYP392A4 3 RNAi (transgenic cotton expressing dsRNA) [ 9 ] Tetranychus urticae (Trombidiformes) P Bean, Tomato Microarray CYP392(A1, A3, B1, B2, B3, D3) 2 , CYP385(C2, C3, C4) 3 , CYP381A2 M / [ 5 ] Transgenic host-plants Heliothis virescens (Lepidoptera) Pieris brassicae (Lepidoptera) P O Glucosinolates ( Arabidopsis ) RNA-seq (Illumina HiSeq 2500) Several members of Clan 3 (CYP6 and CYP9) / [ 31 • ] Tetranychus urticae (Trombidiformes) P Glucosinolates ( Arabidopsis ) RT-qPCR CYP392(A1, A16, D8) 2 RNAi of Tu-CPR [ 6 ] Tupiocoris notatus (Hemiptera) O Jasmonic acid ( Nicotiana attenuata) RNA-seq (Illumina HiSeq 2000) RT-qPCR …”

“…At least 40 genes showed a significant dose-dependent response to glucosinolates, mainly consisting of detoxification enzymes, including P450s and glycosyltransferases [ 30 ]. A follow-up study focused on whether these expression changes are indeed associated with host-plant adaptation or whether they are general stress responses [ 6 ]. Interestingly, none of three selected P450s (CYP392A1, CYP392A16, CYP392D8) that were initially highly upregulated upon short-term host shift [ 30 ] showed a constitutively higher expression after long-term adaptation relative to the non-adapted lines [ 6 ], a pattern that was also found by Wybouw et al for the same mite species and tomato [ 5 ].…”

“…A follow-up study focused on whether these expression changes are indeed associated with host-plant adaptation or whether they are general stress responses [ 6 ]. Interestingly, none of three selected P450s (CYP392A1, CYP392A16, CYP392D8) that were initially highly upregulated upon short-term host shift [ 30 ] showed a constitutively higher expression after long-term adaptation relative to the non-adapted lines [ 6 ], a pattern that was also found by Wybouw et al for the same mite species and tomato [ 5 ]. A. thaliana mutants were also used to compare glucosinolate-induced transcriptomic responses between the generalist Heliothis virescen s and Pieris brassicae, a specialist feeding on glucosinolate-rich diets.…”

“…In addition, specific silencing of a single P450 always needs to be confirmed, as this might be harder to achieve for members of recent P450 ‘blooms’ by cross-silencing. Silencing the gene encoding cytochrome P450 reductase, an obligatory co-enzyme of P450s, is another strategy that has been explored recently with T. urticae P450s [ 6 , 65 ], although this does not allow to study the effect of a single P450 and may result in pleiotropic effects unrelated to detoxification genes. In vivo validation of the role of P450 induction by RNAi is also complicated by uncertainties in timing of both the induction and the silencing, when quantifying the phenotypic effect.…”

“…Gene expression changes in response to phytochemicals and host shifts have been studied both on the short-term, within a generation (induction), as well as on the long-term (adaptation, genetic accommodation) [ 4 •• ]. Surprisingly, only few studies characterized gene expression patterns both upon initial exposure and after adaptation to new host plants [ 5 , 6 , 7 • , 8 , 9 ], with the current consensus that, upon adaptation, mainly genes with unknown function or genes involved in core metabolic pathways show constitutive changes in expression, whereas many detoxification-related genes exhibit within-generation environmental plasticity [ 4 •• , 5 ]. Therefore, there is little evidence that genes induced upon initial exposure, become constitutively overexpressed after adaption, and thus overall patterns of genetic accommodation in arthropod-plant interactions are rare.…”