Convergent adaptive evolution - how insects master the challenge of cardiac glycoside-containing host plants
Convergent adaptive evolution - how insects master the challenge of cardiac glycoside-containing host plants
复制标题
DOI：
10.1111/eea.12340
复制
发表时间：
2015-10-01
影响因子：
1.9
通讯作者：
Flacht, Lara
中科院分区：
文献类型：
--
作者：
Dobler, Susanne;Petschenka, Georg;Flacht, Lara
心糖苷是高毒性植物次级化合物的一个主要例子，它阻断了动物体内必需的跨膜载体Na， k - atp酶。然而，已知有100多种不同目的昆虫以含有这些化合物的植物为食，在许多情况下，这些毒素被额外隔离而没有不良影响。我们研究了昆虫处理心糖苷的适应性是基于单一的生理机制，还是在不同群体中进化出了不同的策略。我们分析了心糖苷适应昆虫的Na， k - atp酶a亚基的基因序列，并筛选了可能改变酶对心糖苷亲和力的氨基酸取代。在5个昆虫目的代表中，我们发现了相同位置上的氨基酸替换，它们的进化差异超过3亿年。尤其引人注目的是，一个组氨酸趋同取代了保守的122位天冬酰胺，这是我们首次在一种锯蝇，Monophadnus latus Costa（膜翅目：十翅目）中报道的，之前在鳞翅目、鞘翅目、半翅目和双翅目中都有观察到。先前的体外表达和酶分析表明，这种取代以及与其他残基的联合取代导致Na， k - atp酶的硬核内酯抗性强烈增加。在M. latus中观察到的对苏氨酸111和组氨酸122的取代是非常有效的，以前只在lygaeid中发现。然而，并不是所有的昆虫都依赖靶点不敏感作为抗性机制。不渗透的肠道或将硬核素从神经组织中排除，神经组织中Na， k - atp酶通过神经膜（昆虫血脑屏障）表达最多，显然代表了另一种策略。本文提供的免疫组织化学数据支持昆虫肠膜中p -糖蛋白样外排转运体的存在，这种转运体可能会阻止化感化学物质（如心桂蕊酯）的摄取。
Cardiac glycosides are a prime example of highly toxic plant secondary compounds, which block an essential transmembrane carrier in animals, the Na, K-ATPase. Nevertheless, over 100 insect species from diverse orders are known to feed on plants containing these compounds and in many cases these toxins are additionally sequestered without ill effect. We investigated whether the insects' adaptations for handling cardiac glycosides are based on a single physiological mechanism or whether various strategies have evolved across groups. We analyzed gene sequences of the Na, K-ATPase a-subunit from cardiac glycoside-adapted insects and screened for amino-acid substitutions which could alter the affinity of the enzyme toward cardiac glycosides. In representatives from five insect orders, separated by over 300 million years of evolutionary divergence, we uncovered amino-acid substitutions at identical positions. Especially striking is the convergent substitution of a histidine for the conserved asparagine at position 122, which we report here for the first time in a sawfly, Monophadnus latus Costa (Hymenoptera: Tenthredinidae), and which was previously observed in the orders Lepidoptera, Coleoptera, Hemiptera, and Diptera. Prior in vitro expression and enzyme assays indicated that this substitution as well as combined substitutions with other residues result in a strongly increased cardenolide resistance of the Na, K-ATPase. The substitutions to threonine 111 and histidine 122 observed in M. latus are highly effective and were previously known only in lygaeid bugs. However, not all insects dealing with dietary cardenolides rely on target-site insensitivity as a mechanism of resistance. An impermeable gut or the exclusion of cardenolides from the nervous tissue with the greatest expression of Na, K-ATPase by the perineurium, the insect blood brain barrier, apparently represent alternative strategies. Immuno-histochemical data presented here support the existence of P-glycoprotein-like efflux transporters in insect gut membranes that might prevent the uptake of allelochemicals like cardenolides.