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

植食性昆虫已经进化出各种各样的策略来对付它们的寄主植物的防御。紫茎泽兰科的植物家族以其芥子油苷-黑芥子酶防御系统而闻名，其中一旦底物与黑芥子酶接触，就会形成有毒的水解产物，如异硫氰酸酯。因此，以紫茎泽兰科为食的昆虫必须以避免形成有毒分解产物的方式代谢芥子油苷。昆虫对植物防御系统的反适应在鳞翅目、半翅目、膜翅目和鞘翅目中表现出多样性。相比之下，几乎没有什么是已知的芥子油苷黑芥子酶系统的解毒在不同的发育阶段的物种，如chrysomelid甲虫，其中幼虫和成人饲料的叶的紫穗槐科。初步实验表明，专家chrysomelid Phaedon cochleariae使用一种新的机制来处理芥子油苷-黑芥子酶系统，该系统与已发现的其他食草动物的所有反适应不同。在这个项目中，我的目标是调查两种菊类植物的芥子油苷代谢，提到的专家和通才，在个体发育。将研究幼体与成体，以测试双重防御的解毒作用是否因变态期间的主要生理重组而在不同阶段之间存在差异。此外，我的目的是研究硫代葡萄糖苷代谢的特异性方面的不同结构的硫代葡萄糖苷。为了回答这些问题，饲养实验将进行标记和未标记的芥子油苷，然后通过化学分析的分解产物。此外，使用基质辅助激光解吸电离质谱成像（MALDI-MSI）对不同喂养持续时间后拍摄的幼虫和成虫切片进行成像，将揭示昆虫中完整的芥子油苷及其代谢物的定位，从而可以确定芥子油苷代谢的速度以及发生代谢的器官。最后，在肠道切片中黑芥子酶活性的测量将揭示这些酶是否在幼虫或成虫通过肠道的过程中被抑制。从草食动物的角度来看，该项目的结果将揭示昆虫适应这种双重植物防御系统的令人印象深刻的不同进化的新见解，并将展示这些适应在个体发育中的变化程度。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苷的加工和黑芥子酶的处理可能导致植物合成如此大量的硫代葡萄糖苷结构和硫代葡萄糖苷水解产物。

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.