Sequestration of phytochemicals by leaf beetles: Selective transport proteins and their influence on diversification processes in plant-herbivore interactions

昆虫可以利用植物衍生的次级代谢产物来防御捕食者。叶甲亚族的叶甲幼虫发育了专门的防御腺体，这些植物代谢物在受到攻击时被转化、储存和释放。螯合过程的详细研究揭示了一个功能网络的运输过程中引导植物衍生的葡萄糖苷通过幼虫体。幼虫肠道的初始吸收似乎是相当非特异性的，这与特定的进口前体到防御腺体形成鲜明对比。排泄器官有助于快速清除体液中过量或无用的化合物。葡萄糖苷的螯合代表了昆虫世界中广泛传播的机制。由于它们的水溶性，这些化合物只能在受控条件下通过膜。转运蛋白改变了它们的底物特异性以转运这些糖基化的植物化学物质。在草食动物对寄主植物的适应过程中，它们处于关键地位。尽管它们具有明显的重要性，但这些转运蛋白至今尚未鉴定或表征。由于到目前为止，已确定的载体网络的Eschomelina物种，这个亚族代表了一个很好的模式系统，研究螯合。对膜转移的详细了解一方面可以与其他隔离昆虫进行比较，另一方面可以发现干扰昆虫和植物共同进化的因素。

Insects can have the capability to use plant derived secondary metabolites for their own defense against predators. The leaf beetle larvae of the subtribe Chrysomelina developed specialized defensive glands in which such plant metabolites are converted, stored and released in case of attack. Detailed studies of the sequestration process revealed a functional network of transport processes guiding plant derived glucosides through the larval body. The initial uptake by the larvae’s intestine seems to be fairly unspecific, which contrasts sharply with the specific import of precursors into the defensive glands. Excretion organs facilitate the rapid clearing of body fluid from excess or unusable compounds. The sequestration of glucosides represents a mechanism widely spread in the insect world. Due to their water solubility these compounds can pass membranes only under controlled conditions. Transport proteins modified their substrate specificity to translocate such glucosylated phytochemicals. With this function they are in a key position during the adaptation process of herbivores to their host plants. Despite their obvious importance such transport proteins haven’t neither identified nor characterized up to now. Because of the carrier network identified in the Chrysomelina species so far, this subtribe represents an excellent model system to study sequestration. The detailed understanding of membrane transfer allows on one hand to draw parallels to other sequestering insects and on the other hand to discover factors that interfere with co-evolution of insects and plants.