Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase
Community-wide convergent evolution in insect adaptation to toxic cardenolides by substitutions in the Na,K-ATPase
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DOI：
10.1073/pnas.1202111109
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发表时间：
2012-08-07
影响因子：
11.1
通讯作者：
Agrawal, Anurag A.
中科院分区：
文献类型：
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作者：
Dobler, Susanne;Dalla, Safaa;Agrawal, Anurag A.
趋同分子进化的程度在很大程度上是未知的，但对理解适应的遗传学至关重要。由于六目昆虫中的食草动物都专门针对这些植物毒素，这些植物毒素通过阻断一种重要的跨膜载体钠泵（Na， k - atp酶）而获得毒性，因此对心髓内酯的靶位不敏感是研究分子趋同的主要候选者。我们研究了18种取食含石心苷植物的昆虫（15属4目）Na， k - atp酶α亚基的基因序列，以筛选可能降低对石心苷敏感性的氨基酸替代。先前在黑脉金斑蝶和金蝇叶甲虫中发现的替代N122H在另外4个物种中被发现具有抗性，分别是fascopeltus和Lygaeus kalmii（异翅目，金蝇科）、cliidomera clivicollis（鞘翅目，金蝇科）和liriomza asclepiadis（双翅目，稻蝇科）。因此，在300兆尔的昆虫分化过程中，对含菊石的植物的特化导致了分子趋同，以适应可能涉及共同进化的适应。我们的筛选揭示了哺乳动物中与硬核内酯结合相关的许多其他替代。我们证实了一些特殊的取代，通过引入五种不同的黑腹果蝇基因结构到易感的真核细胞中，在瓦巴因选择机制下，提供了对果仁内酯的抗性。这些功能分析表明，Q（111）和N-122的联合取代具有协同作用，其抗性比单独取代高出两倍以上，比野生型高出12倍。因此，即使跨越深层的系统发育分支，进化自由度似乎也受到生理约束的限制，因此，相同的分子替换也会产生适应性。
The extent of convergent molecular evolution is largely unknown, yet is critical to understanding the genetics of adaptation. Target site insensitivity to cardenolides is a prime candidate for studying molecular convergence because herbivores in six orders of insects have specialized on these plant poisons, which gain their toxicity by blocking an essential transmembrane carrier, the sodium pump (Na,K-ATPase). We investigated gene sequences of the Na,K-ATPase alpha-subunit in 18 insects feeding on cardenolide-containing plants (spanning 15 genera and four orders) to screen for amino acid substitutions that might lower sensitivity to cardenolides. The replacement N122H that was previously shown to confer resistance in the monarch butterfly (Danaus plexippus) and Chrysochus leaf beetles was found in four additional species, Oncopeltus fasciatus and Lygaeus kalmii (Heteroptera, Lygaeidae), Labidomera clivicollis (Coleoptera, Chrysomelidae), and Liriomyza asclepiadis (Diptera, Agromyzidae). Thus, across 300 Myr of insect divergence, specialization on cardenolide-containing plants resulted in molecular convergence for an adaptation likely involved in coevolution. Our screen revealed a number of other substitutions connected to cardenolide binding in mammals. We confirmed that some of the particular substitutions provide resistance to cardenolides by introducing five distinct constructs of the Drosophila melanogaster gene into susceptible eucaryotic cells under an ouabain selection regime. These functional assays demonstrate that combined substitutions of Q(111) and N-122 are synergistic, with greater than twofold higher resistance than either substitution alone and >12-fold resistance over the wild type. Thus, even across deep phylogenetic branches, evolutionary degrees of freedom seem to be limited by physiological constraints, such that the same molecular substitutions confer adaptation.