The fall armyworm, Spodoptera frugiperda, is an invasive maize pest that has spread from the Americas into Africa and Asia and causes severe crop damage worldwide. Most populations of S. frugiperda show low susceptibility to Bacillus thuringiensis (Bt) Cry1Ab or Cry1Ac toxins, which have been proved to be effective against several other lepidopteran pests. In addition, S. frugiperda has evolved resistance to transgenic maize expressing Cry1Fa toxin. The specificity and toxicity of Cry toxins are determined by their binding to different larval midgut proteins, such as aminopeptidase N (APN), alkaline phosphatase (ALP), and cadherin (CAD), among other proteins, by means of exposed domain II loop regions and also by the domain III β-sheets β-16 and β-22. Here, we analyzed different Cry1Ab mutants with mutations in the domain III β-22 region. Alanine-scanning mutagenesis of this region revealed that all mutants showed increased toxicity against a nonsusceptible Cry1Ab S. frugiperda population. Further analysis of the mutant toxin Cry1AbS587A (bearing a mutation of S to A at position 587) revealed that, compared to Cry1Ab, it showed significantly increased toxicity to three other S. frugiperda populations from Mexico but retained similar toxicity to Manduca sexta larvae. Cry1AbS587A bound to brush border membrane vesicles (BBMV), and its higher toxicity correlated with higher binding affinities to APN, ALP, and CAD recombinant proteins. Furthermore, silencing the expression of APN1 and CAD receptors in S. frugiperda larvae by RNA interference (RNAi) showed that Cry1AbS587A toxicity relied on CAD expression, in contrast to Cry1Ab. These data support the idea that the increased toxicity of Cry1AbS587A to S. frugiperda is in part due to an improved binding interaction with the CAD receptor.

中文翻译：

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苏云金芽孢杆菌Cry1Ab结构域IIIβ-22突变体，对草地贪夜蛾具有增强的毒性（JE Smith）。

秋季粘虫Spodoptera frugiperda是一种入侵性玉米害虫，已从美洲传播到非洲和亚洲，并在全球范围内造成严重的农作物破坏。大部分Srug frugiperda种群对苏云金芽孢杆菌（Bt）Cry1Ab或Cry1Ac毒素的敏感性较低，已被证明可有效对抗其他几种鳞翅目害虫。此外，S。frugiperda已发展出对表达Cry1Fa毒素的转基因玉米的抗性。Cry毒素的特异性和毒性取决于它们与其他幼虫中肠蛋白（例如氨基肽酶N（APN），碱性磷酸酶（ALP）和钙粘蛋白（CAD）等）的结合，并通过暴露的域II环域来确定以及结构域III的β-折叠β-16和β-22。在这里，我们分析了在结构域IIIβ-22区域具有突变的不同Cry1Ab突变体。该区域的丙氨酸扫描诱变表明，所有突变体均显示出对不敏感的Cry1Ab S. frugiperda种群的毒性增加。进一步分析突变体毒素Cry1AbS587A（在587位的S突变为A）显示，与Cry1Ab相比，它对其他三种毒素的毒性显着增加来自墨西哥的Srug frugiperda种群，但对曼杜卡六倍体幼虫保留了相似的毒性。Cry1AbS587A绑定到刷状边界膜囊泡（BBMV），其较高的毒性与对APN，ALP和CAD重组蛋白的较高结合亲和力相关。此外，通过RNA干扰（RNAi）抑制S. frugiperda幼虫中APN1和CAD受体的表达，表明Cry1AbS587A毒性与Cry1Ab相反，依赖于CAD表达。这些数据支持了Cry1AbS587A对S. frugiperda的毒性增加的想法，部分原因是与CAD受体的结合相互作用得以改善。