Gene duplications circumvent trade-offs in enzyme function: Insect adaptation to toxic host plants
Gene duplications circumvent trade-offs in enzyme function: Insect adaptation to toxic host plants
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DOI：
10.1111/evo.13077
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发表时间：
2016-12-01
期刊：
影响因子：
3.3
通讯作者：
Dobler, Susanne
中科院分区：
文献类型：
--
作者：
Dalla, Safaa;Dobler, Susanne
草食性昆虫及其对植物毒素的适应性为研究共同进化相互作用中的性状遗传基础提供了极好的机会。对强心内酯的靶位点不敏感性在六个昆虫目中趋同进化，涉及Na，K-ATP酶基因中的相同取代和重复的趋同基因复制。大型马利筋虫Oncopeltus fasciatus具有三个拷贝的Na，K-ATP酶a亚基基因，其在强心内酯的结合口袋中具有不同数量的氨基酸取代。为了分析这些取代对腰果酚抗性的影响，并推断基因功能中可能的权衡，我们在体外表达了果蝇对腰果酚敏感的Na，K-ATP酶，并在O.带条肌随着置换数目的增加，Na，K-ATPase对标准Cardenoprotein的敏感性逐步降低。同时，酶的总体活性随着心肌炎抗性的增加而显著降低，并且仅Na，K-ATP酶α 1C拷贝的最少取代的模拟物保持与野生型酶类似的活性。我们的结果表明，O. Fasciatus在功能上已经分化，使得能够对膳食Cardenolides进行特定适应，同时保持这种关键离子载体的功能。
Herbivorous insects and their adaptations against plant toxins provide striking opportunities to investigate the genetic basis of traits involved in coevolutionary interactions. Target site insensitivity to cardenolides has evolved convergently across six orders of insects, involving identical substitutions in the Na, K-ATPase gene and repeated convergent gene duplications. The large milkweed bug, Oncopeltus fasciatus, has three copies of the Na, K-ATPase a-subunit gene that bear differing numbers of amino acid substitutions in the binding pocket for cardenolides. To analyze the effect of these substitutions on cardenolide resistance and to infer possible trade-offs in gene function, we expressed the cardenolide-sensitive Na, K-ATPase of Drosophila melanogaster in vitro and introduced four distinct combinations of substitutions observed in the three gene copies of O. fasciatus. With an increasing number of substitutions, the sensitivity of the Na, K-ATPase to a standard cardenolide decreased in a stepwise manner. At the same time, the enzyme's overall activity decreased significantly with increasing cardenolide resistance and only the least substituted mimic of the Na, K-ATPase alpha 1C copy maintained activity similar to the wild-type enzyme. Our results suggest that the Na, K-ATPase copies in O. fasciatus have diverged in function, enabling specific adaptations to dietary cardenolides while maintaining the functionality of this critical ion carrier.