Department of Entomology, Cornell University, Geneva, NY 14456, USA.
Department of Entomology, Cornell University, Geneva, NY 14456, USA.
J Insect Physiol. 2019 Aug-Sep;117:103897. doi: 10.1016/j.jinsphys.2019.103897. Epub 2019 Jun 11.
The insect midgut peritrophic membrane (or peritrophic matrix) (PM) is an extracellular structure, lining the midgut epithelium. The PM facilitates the food digestion process and plays important roles in insect-microbe interactions as a barrier against microbial pathogens. The soil bacterium, Bacillus thuringiensis (Bt), and its proteinaceous toxins are widely used for insect control. To understand the protective role of PM in insects against Bt toxins, the effect of PM on larval susceptibility to Bt toxin Cry1Ac was examined in Cry1Ac-susceptible and -resistant strains of the cabbage looper, Trichoplusia ni. The PM in T. ni was disrupted, using a baculovirus enhancin (TnGV enhancin) to degrade the major PM mucin protein IIM and a chitin binding chemical, Calcofluor, to inhibit the binding of PM proteins to chitin. Bioassays of the susceptibility of T. ni larvae to Cry1Ac with treatment of TnGV enhancin showed significantly increased larval mortality in both the Cry1Ac susceptible and resistant strains, confirming that the PM is a protective barrier to the passage of Cry1Ac and plays a protective role against the toxin. However, treatment of T. ni larvae with Calcofluor significantly reduced the larval susceptibility to Cry1Ac. The level of mortality reduction by treatment with Calcofluor was more significant in the resistant T. ni strains than in the susceptible strain. The mechanism for the decrease of susceptibility to Cry1Ac in T. ni treated with Calcofluor needs to be understood. It may result from binding of the toxin to the over expressed PM proteins, preventing the Cry1Ac from reaching the midgut receptor for the toxin or from potential binding of Calcofluor to the midgut receptor for Cry1Ac, leading to inhibition of the toxicity of Cry1Ac in larvae.
昆虫中肠围食膜（或围食基质）（PM）是一种细胞外结构，排列在中肠上皮细胞的内表面。PM 有助于食物消化过程，并在昆虫与微生物相互作用中作为抵御微生物病原体的屏障发挥重要作用。土壤细菌苏云金芽孢杆菌（Bt）及其蛋白毒素被广泛用于昆虫控制。为了了解 PM 在昆虫抵抗 Bt 毒素中的保护作用，研究了 PM 对小菜蛾幼虫对 Bt 毒素 Cry1Ac 敏感性的影响，小菜蛾是 Cry1Ac 敏感和抗性品系。使用杆状病毒增强子（TnGV 增强子）降解主要 PM 粘蛋白 IIM 和几丁质结合化学物质 Calcofluor 来破坏 T. ni 的 PM，从而破坏 T. ni 的 PM。用 TnGV 增强子处理小菜蛾幼虫对 Cry1Ac 敏感性的生物测定表明，在 Cry1Ac 敏感和抗性品系中，幼虫死亡率均显著增加，证实 PM 是 Cry1Ac 穿透的保护屏障，并对毒素起到保护作用。然而，用 Calcofluor 处理小菜蛾幼虫显著降低了 Cry1Ac 的幼虫敏感性。Calcofluor 处理降低 Cry1Ac 敏感性的程度在抗性 T. ni 品系中比在敏感品系中更为显著。需要了解用 Calcofluor 处理的 T. ni 对 Cry1Ac 敏感性降低的机制。它可能是由于毒素与过度表达的 PM 蛋白结合，阻止 Cry1Ac 到达毒素的中肠受体，或者 Calcofluor 与 Cry1Ac 的中肠受体潜在结合，从而抑制幼虫中 Cry1Ac 的毒性。
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