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Crop Biotech Update

Binding Characterization of Cry Proteins to the Brush Border Membrane Vesicles of Insect Pests

September 25, 2013

Cry proteins from the common soil bacterium Bacillus thuringiensis are effective biological insecticides against specific insect pests. However, resistance of the pests to Cry proteins could evolve through time, manifested by decreased binding of the Cry proteins to target sites in brush border membranes of the larva midgut. Cry proteins with different binding sites is an effective means to delay resistance evolution. Thus, Yong-jun Zhang from Chinese Academy of Agricultural Sciences and other scientists studied the binding characteristics of Cry proteins to different insect pests.

Bioassay results showed that the toxicity of different Cry proteins ranked differently for each insect species. The toxicity ranking observed were as follows: cotton bollworm (Helicoverpa armigera)-Cry1Ac>Cry1Ab>Cry2Ab; Beet armyworm (Spodoptera exigua)-Cry1B>Cry1C>Cry2Ab; Oriental leafworm (S. litura)-Cry2Ab>Cry1B> Cry1C. Only Cry2Ab was toxic to black cutworm (Agrotis ipsilon). Binding experiments were conducted with Cry1Ab, Cry1Ac, Cry1B, Cry1C, Cry2Ab and the brush border membrane vesicles (BBMV) of cotton bollworm, beet armyworm, oriental leafworm, and black cutworm. Results showed that the binding of Cry1Ab and Cry1Ac was stronger by increasing concentrations of cotton bollworm BBMV. The binding of Cry1B was saturable by incubating with increasing concentrations of beet armyworm BBMV. The binding of Cry proteins was found to be non-saturable by incubating with increasing concentrations of oriental leafworm and black cutworm BBMV. In contrast, Cry1B and Cry1C showed some combination with the BBMV of oriental leafworm, and a specific concentration of Cry2Ab could bind to the BBMV of black cutworm.

These findings suggest that combining specific Cry genes in biotech crops could widen the spectrum of insecticide effectiveness and delay insect resistance evolution.

Read the research article at http://www.sciencedirect.com/science/article/pii/S209531191360427X.