Gene duplications and subfunctionalization in response to challenges by dietary cardiac glycosides in phytophagous insects
Evolution, Anthropology
Final Report Abstract
The adaptations animals have evolved to cope with toxic cardiac glycosides in their diet represent a fascinating case of convergent evolution. These toxins have a precise target, the Na,K-ATPase (NKA), an essential ion carrier across all of the animal kingdom. Blocking of the NKA by cardiac glycosides is highly disruptive and eventually fatal. Nevertheless many insects have adapted to feeding on cardiac glycoside containing plants and may even use the toxins for their own anti-predator defense. This is the case for the large milkweed bug, Oncopeltus fasciatus, whose NKA is strongly resistant to the inhibitory effect of cardiac glycosides. The resistance is caused by amino acid substitutions in the binding site for cardiac glycosides on the a1-subunit of the NKA. In addition, O. fasciatus has four gene copies of the a1-subunit that differ in the number and identity of amino acid substitutions in the cardiac glycoside binding site and have to dimerize with one of four β-subunits to form a functional enzyme. This project focussed on the importance that these different subunits play for the insect's adaptation to cardiac glycosides. As we could show the a1-subunits strongly differ not only in their resistance to cardiac glycosides but also in their ion pumping activity and can further be modulated by the identity of the β-subunit they are combined with. The stepwise gene duplications that gave rise to the four a1-subunits led to increasingly more resistant forms of the enzyme. Most intriguingly resistance to typical cardiac glycosides of the bugs' host plants increased more strongly than to a non-host standard cardiac glycoside argueing for a stepwise escalation of the insects' counter-defenses to their host plants' toxins. We further investigated the tissue specific distribution of the various subunits of the NKA by immunocytochemistry and LC-MS/MS proteomic techniques. This yielded insights into the naturally occurring combinations of the subunits and allows deductions on their functional roles. Surprisingly higher order complexes of the NKA subunits as well as isolated occurrences of both a1 and β-subunits were supported by our data. The fine scale distribution of the β-subunits supports their involvement in the formation of septate junctions, a finding congruent with reports on Drosophila. Knock-down of β-subunits by RNA interference resulted in serious molting defects of the bugs and an altered fine structure of their tracheae - both phenomena that may be explained by malformation of epithelia due to disrupted septate junctions. An analysis of co-occurrence of the obligatory septate junction protein coracle and the beta subunits further corroborates a tissue specific involvement of the different β-subunits in septate junctions.
Publications
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Concerted evolution reveals co-adapted amino acid substitutions in Na+K+-ATPase of frogs that prey on toxic toads. Current Biology, 31(12), 2530-2538.e10.
Mohammadi, Shabnam; Yang, Lu; Harpak, Arbel; Herrera-Álvarez, Santiago; del Pilar Rodríguez-Ordoñez, María; Peng, Julie; Zhang, Karen; Storz, Jay F.; Dobler, Susanne; Crawford, Andrew J. & Andolfatto, Peter
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Constraints on the evolution of toxin-resistant Na,K-ATPases have limited dependence on sequence divergence. PLOS Genetics, 18(8), e1010323.
Mohammadi, Shabnam; Herrera-Álvarez, Santiago; Yang, Lu; Rodríguez-Ordoñez, María del Pilar; Zhang, Karen; Storz, Jay F.; Dobler, Susanne; Crawford, Andrew J. & Andolfatto, Peter
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Epistatic Effects Between Amino Acid Insertions and Substitutions Mediate Toxin resistance of Vertebrate Na+,K+-ATPases. Molecular Biology and Evolution, 39(12).
Mohammadi, Shabnam; Özdemir, Halil İbrahim; Ozbek, Pemra; Sumbul, Fidan; Stiller, Josefin; Deng, Yuan; Crawford, Andrew J.; Rowland, Hannah M.; Storz, Jay F.; Andolfatto, Peter & Dobler, Susanne
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Functional evidence supports adaptive plant chemical defense along a geographical cline. Proceedings of the National Academy of Sciences, 119(25).
Agrawal, Anurag A.; Espinosa, del Alba Laura; López-Goldar, Xosé; Hastings, Amy P.; White, Ronald A.; Halitschke, Rayko; Dobler, Susanne; Petschenka, Georg & Duplais, Christophe
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Knockdown of Na,K‐ATPaseβ‐subunits inOncopeltus fasciatusinduces molting problems and alterations in tracheal morphology. Insect Science, 30(2), 375-397.
Herbertz, Marlena; Lohr, Jennifer; Lohr, Christian & Dobler, Susanne
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Na,K-ATPase α1 and β-subunits show distinct localizations in the nervous tissue of the large milkweed bug. Cell and Tissue Research, 388(3), 503-519.
Herbertz, Marlena; Harder, Sönke; Schlüter, Hartmut; Lohr, Christian & Dobler, Susanne
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Coevolutionary escalation led to differentially adapted paralogs of an insect's Na,K‐ATPase optimizing resistance to host plant toxins. Molecular Ecology, 33(14).
Herbertz, Marlena; Dalla, Safaa; Wagschal, Vera; Turjalei, Rohin; Heiser, Marlies & Dobler, Susanne
