ABCB transporters as key adaptations of herbivorous insects to toxic cardiac glycosides

ABCB 转运蛋白是草食性昆虫对有毒强心苷的关键适应

• 批准号: 513035770
• 负责人: Professorin Dr. Susanne Dobler
• 金额: --
• 依托单位: Abteilung Molekulare Evolutionsbiologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/513035770?language=en
• 关键词: ABCB; transporters; key; adaptations; herbivorous

Although plants have evolved a plethora of noxious secondary compounds to ward off their herbivore enemies, these defenses are not insurmountable and even the most toxic plants have some insects that manage to feed on them. One such highly toxic class of compounds are cardiac glycosides (cardenolides and bufadienolides). Adaptation to these compounds has become a text book example for convergent evolution of resistance that circumvents noxious effects by target-site insensitivity of the Na,K-ATPase. However, it is obvious that in addition to target-site insensitivity transport mechanisms play a decisive role in the adaptation to these toxins. Such transport mechanisms may prevent uptake from the gut, regulate excretion, protect sensitive tissues or guarantee the transfer into specialized insensitive compartments of the body. Our current data strongly support a role of ATP-binding cassette subfamily B (ABCB) transporters as decisive players in the transport network mediating adaptation to cardiac glycosides. The aim of this study is to elucidate the importance of ABCB proteins for cardenolide transport in the large milkweed bug, Oncopeltus fasciatus. O. fasciatus is adapted to the cardenolides in its food plants and is insensitive to their inhibiting effect on the Na,K-ATPase. The bugs are aposematically colored and sequester the toxins in their defense fluids which are released upon attack by predators. This necessitates a transport from the gut into the hemolymph and further on against a concentration gradient into the storage compartments of the defense fluids. At the same time the nervous tissue needs to be protected by active efflux carriers from an accumulation of cardenolides that might impair nerve excitability. This project starts by identifying ABCB full and half transporters from transcriptomes of O. fasciatus followed by a determination of their tissue distributions and a functional characterization by in vivo and in vitro assays. RNAi mediated knock-down experiments combined with functional tests of excretion and resorption by the Malpighian tubules will be used to analyze the importance of specific gene transcripts. Effects of transcript knock-down combined with injection or oral administration of cardenolides will in addition be investigated by phenotypic screening and HPLC analyses of hemolymph and defense fluids. The study will thereby elucidate the transport network for cardenolides and further our understanding of the relevance of ABCB transporters in the adaptations of insect herbivores to toxic plant compounds. This contributes valuable knowledge to the still widely under-investigated processes of xenobiotic transport across insect epithelia.

虽然植物已经进化出了大量有毒的次生化合物来抵御食草动物的敌人，但这些防御并不是不可逾越的，即使是最有毒的植物也有一些昆虫设法以它们为食。其中一类剧毒的化合物是心脏苷类化合物（硬核内酯和蟾二烯内酯）。对这些化合物的适应已经成为耐药趋同进化的教科书范例，通过Na， k - atp酶的靶位点不敏感来规避有害效应。然而，很明显，除了靶位不敏感外，转运机制在对这些毒素的适应中起决定性作用。这种转运机制可能阻止肠道吸收，调节排泄，保护敏感组织或保证转移到身体的专门不敏感的隔室。我们目前的数据强烈支持atp结合盒亚家族B （ABCB）转运蛋白在转运网络中介导对心脏糖苷的适应中起决定性作用。本研究的目的是阐明ABCB蛋白在大型乳草虫（Oncopeltus fasciatus）的硬核内酯运输中的重要性。筋膜虫对其食用植物中的心桂素类植物具有适应性，对其对Na， k - atp酶的抑制作用不敏感。这些臭虫有警示性的颜色，并将毒素隔离在它们的防御液中，这些毒素在受到捕食者的攻击时释放出来。这就需要从肠道运输到血淋巴，并进一步对抗浓度梯度进入防御液的储存室。同时，神经组织需要受到主动外排载体的保护，以防止硬核内酯的积累可能损害神经兴奋性。本项目首先从筋膜棘鱼转录组中鉴定ABCB全转运体和半转运体，然后通过体内和体外试验确定其组织分布和功能表征。RNAi介导的敲除实验结合马氏小管排泄和吸收的功能测试将用于分析特定基因转录本的重要性。此外，还将通过表型筛选和高效液相色谱分析血淋巴和防御液来研究转录本敲除联合注射或口服硬核内酯的效果。因此，该研究将阐明核桃内酯的转运网络，并进一步了解ABCB转运体在昆虫食草动物对有毒植物化合物的适应中的相关性。这为仍在广泛研究的昆虫上皮的外源性运输过程提供了有价值的知识。