Counteradaptations of chrysomelid beetles to host plant defences over the ontogeny from larvae to adults

食草性昆虫已经进化出各种策略来应对寄主植物的防御。十字花科植物家族以其硫代葡萄糖苷-黑芥子酶防御系统而闻名，在该系统中，一旦底物与黑芥子酶接触，就会形成有毒的水解物，如异硫氰酸盐。因此，以十字花科植物为食的昆虫必须以一种避免形成有毒分解产物的方式代谢硫代葡萄糖苷。在鳞翅目、半翅目、膜翅目和一种鞘翅目中，昆虫对植物防御系统的反适应已被揭示出迷人的多样性。相比之下，对硫代葡萄糖苷-黑芥子酶系统在金龟子等物种不同发育阶段的解毒作用几乎一无所知，金龟子的幼虫和成虫都以十字花科植物的叶子为食。初步实验表明，专业的蝶形虫Phaedon cochleariae使用了一种新的机制来处理硫代葡萄糖苷-黑芥子酶系统，这与已发现的其他十字花科食性动物的所有反适应不同。在这个项目中，我的目标是研究上述专家和多面手这两种金龟子个体发育过程中硫代葡萄糖苷的代谢。将对幼虫和成虫进行研究，以测试双重防御的解毒作用是否会因变态过程中的主要生理重组而在不同阶段有所不同。此外，我的目的是研究硫代葡萄糖苷代谢的特异性与硫代葡萄糖苷的不同结构有关。为了回答这些问题，将用标记和未标记的硫代葡萄糖酸盐进行喂养实验，然后对分解产物进行化学分析。此外，使用基质辅助激光解吸电离-质谱仪(MALDI-MSI)对不同取食时间后的幼虫和成虫的切片进行成像，将揭示完整的硫代葡萄糖苷及其代谢物在昆虫中的定位，从而确定硫代葡萄糖苷的代谢速度以及发生新陈代谢的器官。最后，测量肠道切片中的黑芥子酶活性将揭示这些酶在幼虫或成虫通过肠道的过程中是否受到抑制。从食草动物的角度来看，该项目的结果将揭示昆虫对这种双重植物防御系统的适应的令人印象深刻的分歧进化，并将展示这些适应在多大程度上改变了个体发育。从植物进化的角度来看，我们可以了解到昆虫对不同硫代葡萄糖酸盐的处理和对芥子糖酶的处理在多大程度上可能导致植物合成如此多种类的硫代葡萄糖苷结构和硫代葡萄糖苷水解物。

Herbivorous insects have evolved various strategies to deal with the defences of their host plants. The plant family of Brassicaceae is well known for its glucosinolate-myrosinase defence system, in which toxic hydrolysis products such as isothiocyanates are formed once the substrate comes into contact with the myrosinase enzymes. Thus, insects feeding on Brassicaceae must metabolise the glucosinolates in a way that they avoid the formation of toxic breakdown products. A fascinating diversity of insect counteradaptations to the plant defence system has been revealed within the Lepidoptera, and in species of Hemiptera, Hymenoptera and one Coleoptera. In contrast, almost nothing is known about the detoxification of the glucosinolate-myrosinase system in different developmental stages of species such as chrysomelid beetles, in which both larvae and adults feed on leaves of Brassicaceae. Preliminary experiments indicate that the specialist chrysomelid Phaedon cochleariae uses a novel mechanism of dealing with the glucosinolate-myrosinase system which is distinct from all counteradaptations that have been discovered for other Brassicaceae-feeders. In this project, I aim to investigate the glucosinolate metabolism of two chrysomelid species, the mentioned specialist and a generalist, over ontogeny. Larvae versus adults will be studied to test whether the detoxification of the dual defence may differ between stages because of the major physiological reorganisation during metamorphosis. Furthermore, I aim to study the specificity of glucosinolate metabolism with regard to the different structures of glucosinolates. To answer these questions, feeding experiments will be carried out with labelled and unlabelled glucosinolates followed by chemical analysis of breakdown products. Additionally, imaging of sections of larvae and adults, taken after different feeding durations, using matrix assisted laser desorption ionisation-mass spectrometry imaging (MALDI-MSI) will reveal the localisation of intact glucosinolates and their metabolites in the insects, allowing to identify the speed with which glucosinolates are metabolised as well as the organs in which metabolism takes place. Finally, measurements of myrosinase activities in gut sections will reveal whether these enzymes are inhibited during the passage through the gut in larvae or adults. From the herbivore perspective, the results of the project will reveal novel insight in the impressive divergent evolution of insect adaptations to this dual plant defence system and will demonstrate in how far these adaptations change over ontogeny. From a plant evolutionary perspective, we may learn in how far the insect processing of different glucosinolates and dealing with the myrosinases may lead to the fact that plants synthesise such a large variety of glucosinolate structures and glucosinolate hydrolysis products.