Jin Tingting, Chang Xue, Gatehouse Angharad M R, Wang Zhenying, Edwards Martin G, He Kanglai
The State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
Newcastle Institute for Research on Sustainability, School of Biology, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK.
Toxins (Basel). 2014 Sep 11;6(9):2676-93. doi: 10.3390/toxins6092676.
Development of resistance in target pests is a major threat to long-term use of transgenic crops expressing Bacillus thuringiensis (Bt) Cry toxins. To manage and/or delay the evolution of resistance in target insects through the implementation of effective strategies, it is essential to understand the basis of resistance. One of the most important mechanisms of insect resistance to Bt crops is the alteration of the interactions between Cry toxins and their receptors in the midgut. A Cry1Ac-selected strain of Asian corn borer (ACB), Ostrinia furnacalis, a key pest of maize in China, evolved three mutant alleles of a cadherin-like protein (OfCAD) (MPR-r1, MPR-r2 and MPR-r3), which mapped within the toxin-binding region (TBR). Each of the three mutant alleles possessed two or three amino acid substitutions in this region, especially Thr1457→Ser. In highly resistant larvae (ACB-Ac200), MPR-r2 had a 26-amino acid residue deletion in the TBR, which resulted in reduced binding of Cry1Ac compared to the MPR from the susceptible strain, suggesting that the number of amino acid deletions influences the level of resistance. Furthermore, downregulation of OfCAD gene (ofcad) transcription was observed in the Cry1Ac resistant strain, ACB-Ac24, suggesting that Cry1Ac resistance in ACB is associated with the downregulation of the transcript levels of the cadherin-like protein gene. The OfCAD identified from ACB exhibited a high degree of similarity to other members of the cadherin super-family in lepidopteran species.
目标害虫产生抗性是对表达苏云金芽孢杆菌（Bt）Cry毒素的转基因作物长期使用的重大威胁。为了通过实施有效策略来管理和/或延缓目标昆虫抗性的进化，了解抗性的基础至关重要。昆虫对Bt作物产生抗性的最重要机制之一是Cry毒素与其中肠受体之间相互作用的改变。中国玉米主要害虫亚洲玉米螟（Ostrinia furnacalis）的一个Cry1Ac选择品系进化出了一种类钙粘蛋白（OfCAD）的三个突变等位基因（MPR-r1、MPR-r2和MPR-r3），这些等位基因定位于毒素结合区域（TBR）内。这三个突变等位基因在该区域各自具有两个或三个氨基酸替换，尤其是Thr1457→Ser。在高抗性幼虫（ACB-Ac200）中，MPR-r2在TBR中有一个26个氨基酸残基的缺失，与敏感品系的MPR相比，这导致Cry1Ac的结合减少，表明氨基酸缺失的数量影响抗性水平。此外，在Cry1Ac抗性品系ACB-Ac24中观察到OfCAD基因（ofcad）转录下调，这表明亚洲玉米螟对Cry1Ac的抗性与类钙粘蛋白基因转录水平的下调有关。从亚洲玉米螟中鉴定出的OfCAD与鳞翅目物种中钙粘蛋白超家族的其他成员表现出高度相似性。
