Functional analysis of a bitter gustatory receptor highly expressed in the larval maxillary galea of Helicoverpa armigera.
Functional analysis of a bitter gustatory receptor highly expressed in the larval maxillary galea of Helicoverpa armigera.
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DOI：
10.1371/journal.pgen.1010455
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发表时间：
2022-10
期刊：
影响因子：
4.5
通讯作者：
中科院分区：
文献类型：
--
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许多植物次生物质是昆虫的取食阻遏物，在昆虫对寄主植物的选择中起着关键作用。植食性昆虫的味觉感受器中含有对阻遏物敏感的味觉神经元，但阻遏物化学感受的分子基础尚不清楚。我们研究了Gr 180的功能，最高表达的苦味味觉受体在棉铃虫幼虫的上颌帽状体。使用爪蟾卵母细胞表达系统和双电极电压钳的功能分析表明，表达Gr 180的卵母细胞响应香豆素。尖端记录结果表明，五龄幼虫上颚的内侧柱锥感器对香豆素有明显的电生理反应。双选择摄食生物测定证实，香豆素抑制幼虫摄食。一株H.使用CRISPR-Cas9系统建立了具有截短的Gr 180蛋白（Gr 180 −/−）的棉铃虫。Gr 180 −/−的茎锥内侧感器对香豆素的反应几乎消失，对芥子苷和士的宁的反应也显著降低。Gr 180基因敲除可减轻香豆素、芥子苷和士的宁的拒食作用。因此，我们得出结论，Gr 180是一个响应香豆素的受体，也参与传感sinigrin和士的宁。这些结果加深了我们对植食性昆虫味觉感受机制的理解。植食性昆虫避免食用大多数植物，因为存在令人不快的次级化合物，这引入了昆虫如何感知这些化合物的问题。棉铃虫是旧大陆一种严重的农作物害虫，其幼虫主要取食多种寄主植物的生殖器官。在这里，我们研究味觉受体，Gr 180，在棉铃虫幼虫的味觉器官中高度表达的功能。表达Gr 180的青蛙卵母细胞选择性地响应香豆素，一种广泛存在于植物中的苦味化合物。当该基因被敲除后，内侧茎锥感器中的阻遏细胞对香豆素的反应消失，对另外两种阻遏物sinigrin和士的宁的反应也减弱。而香豆素对侧茎锥感器中蔗糖细胞的抑制作用不受影响。同时，在基因敲除的毛虫中，对这些化合物的厌恶性摄食反应减少。这些发现对于揭示植食性昆虫对寄主的选择机制和利用取食抑制剂防治害虫具有重要意义。
Many plant secondary substances are feeding deterrents for insects and play a key role in the selection of host plants. The taste sensilla of phytophagous insects contain gustatory sensory neurons sensitive to deterrents but the molecular basis of deterrent chemoreception remains unknown. We investigated the function of Gr180, the most highly expressed bitter gustatory receptor in the maxillary galea of Helicoverpa armigera larvae. Functional analyses using the Xenopus oocyte expression system and two-electrode voltage clamp revealed that the oocytes expressing Gr180 responded to coumarin. Tip recording results showed that the medial sensilla styloconica of the maxilla of fifth instar larvae exhibited electrophysiological responses to coumarin. Two-choice feeding bioassays confirmed that coumarin inhibited larval feeding. A homozygous mutant strain of H. armigera with truncated Gr180 proteins (Gr180−/−) was established using the CRISPR-Cas9 system. The responses of the medial sensilla styloconica in Gr180−/− to coumarin were almost abolished, and the responses to sinigrin and strychnine were also significantly decreased. Knockout of Gr180 alleviated the feeding deterrent effects of coumarin, sinigrin, and strychnine. Thus, we conclude that Gr180 is a receptor responding to coumarin,and also participates in sensing sinigrin and strychnine. These results enhance our understanding of the gustatory sensing mechanisms of phytophagous insects to deterrents. Phytophagous insects avoid eating most plants because of the presence of distasteful secondary compounds, which introduces the question of how these compounds are perceived by insects. The cotton bollworm is a very serious crop pest in the Old World, and its caterpillars mainly feed on the reproductive organs of many host plants. Here, we study the function of a gustatory receptor, Gr180, highly expressed in the taste organ of Helicoverpa armigera caterpillars. The oocytes of frogs expressing Gr180 selectively responded to coumarin, a bitter compound widely exist in plants. When this gene was knocked out, the response of the deterrent cells in the medial styloconic sensilla to coumarin disappeared, and the responses to other two deterrents sinigrin and strychnine were also attenuated. However, the inhibitory effect of coumarin on the sucrose cells in the lateral styloconic sensilla was not affected. At the same time, the aversive feeding responses to these compounds were reduced in the knockout caterpillars. These findings are important for revealing the mechanisms of host selection in herbivorous insects and the use of feeding deterrents for pest control.
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