Roles of insect midgut cadherin in Bt intoxication and resistance

Authors: Fabrick, Jeffrey; WU, YIDONG - Nanjing Agricultural University

Submitted to: CABI Crop Protection Compendium
Publication Type: Book / Chapter
Publication Acceptance Date: 8/6/2014
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/3128424
Citation: Fabrick, J.A., Wu, YiDong. 2015. Roles of insect midgut cadherin in Bt intoxication and resistance. In: Soberon, M., Gao, Y., Bravo, A., editors. Bt resistance-characterization and strategies for GM crops expressing Bacillus thuringiensis toxins. Boston, MA: CABI Crop Protection Compendium. 4:69-86.

Interpretive Summary: Genetically engineered crops (Bt crops) that produce insecticidal proteins of the bacterium, Bacillus thuringiensis, are used for control of several major insect pests. Widespread use of Bt crops has provided benefits including improved yields, and compared to conventional insecticides, reduced impacts on beneficial insects, the environment, and people. However, development of resistance to the Bt toxins by target pests threatens the long-term sustainability of Bt crops as an insect control tool. Insects resistant to Bt toxins have been selected in the laboratory, and resistant pests have been identified in the field in several regions of the world. Although the means by which these insects resist the Bt toxin has not been identified in many cases, a common mechanism involves changes to "cell adhesion proteins," or cadherins, that bind the Bt toxin in the insect gut. These changes, or mutations, alter the binding of Bt toxins to the cadherin protein and can thereby result in resistance to Bt toxins. Here, we highlight the roles of insect gut cadherins in Bt toxin action and review cases where changes in cadherin are involved in resistance to Bt toxins. Furthermore, we emphasize the importance of understanding the underlying basis of Bt toxin activity, and mechanisms of resistance to Bt toxins, and their implications to efforts to manage the development of Bt resistance in major crop pests.

Technical Abstract: Genetically engineered crops producing Bacillus thuringiensis (Bt) proteins for insect control target major insect pests. Bt crops have improved yield and reduced risks associated with conventional insecticides; however, the evolution of resistance to Bt toxins by target pests threatens the long-term success of such transgenic crops. Insects resistant to Cry toxins have been selected in the laboratory and field-evolved resistance has been reported for economically important insects in several regions of the world. Although the mechanisms of resistance have not been reported for all cases, the most common mechanism involves changes in larval midgut target sites that likely reduce binding to Bt toxins. Binding of Cry toxins to midgut cadherin represents an important step in Bt intoxication for many insects and mutations in the cadherin gene can result in resistance to Bt toxins. Here, we highlight the roles insect midgut cadherins play in Bt Cry intoxication and review cases where changes in cadherin are involved with resistance to Cry toxins. Furthermore, we emphasize the importance of understanding the underlying molecular basis of Bt intoxication and resistance to Bt and the implications of fundamental knowledge to resistance management strategies.