Physiological and molecular adaptations of phytophagous insects to cardiac glycosides in their host plants

点击翻译按钮获取中文摘要

It is largely unknown to what extent key adaptations are caused by convergent evolution on the molecular level. We here examine in how far insects convergently evolved the same adaptations to tolerate toxic cardenolides that they either encounter in their host plants or that they produce as autogenous defense compounds. The main target site of cardenolides, the Na,K-ATPase, may elude toxicity by several amino acid substitutions that prevent a blocking by cardenolides. So far, we detected strongly convergent evolution at the molecular level. On the other hand, various insects evolved fundamentally different strategies to circumvent cardenolide toxicity. We now focus on convergent and so far undescribed gene duplication events leading in different groups (bugs and leaf beetles) to tissue specific expression of isoforms of the Na,K-ATPase that differ in cardenolide resistance. Secondly, we analyze which highly efficient carriers protect the sensitive nervous tissue against the toxins and characterized them on the physiological and molecular level. According to studies in mammals and our own data, carriers of two gene families, the organic anion transporting polypeptides (Oatps) and P-glycoproteins (PGPs) are the most plausible candidates for this. A comparison of leaf beetle species that are naturally exposed or not exposed to cardenolides makes it possible to discriminate between specific convergent adaptations to cardenolides and generell avoidance mechanisms against xenobiotics.