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Originally published in Science Express on 1 November 2007
Science 7 December 2007:
Vol. 318. no. 5856, pp. 1640 - 1642
DOI: 10.1126/science.1146453
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Reports

Engineering Modified Bt Toxins to Counter Insect Resistance

Mario Soberón,1* Liliana Pardo-López,1 Idalia López,1 Isabel Gómez,1 Bruce E. Tabashnik,2 Alejandra Bravo1*

The evolution of insect resistance threatens the effectiveness of Bacillus thuringiensis (Bt) toxins that are widely used in sprays and transgenic crops. Resistance to Bt toxins in some insects is linked with mutations that disrupt a toxin-binding cadherin protein. We show that susceptibility to the Bt toxin Cry1Ab was reduced by cadherin gene silencing with RNA interference in Manduca sexta, confirming cadherin's role in Bt toxicity. Native Cry1A toxins required cadherin to form oligomers, but modified Cry1A toxins lacking one {alpha}-helix did not. The modified toxins killed cadherin-silenced M. sexta and Bt-resistant Pectinophora gossypiella that had cadherin deletion mutations. Our findings suggest that cadherin promotes Bt toxicity by facilitating toxin oligomerization and demonstrate that the modified Bt toxins may be useful against pests resistant to standard Bt toxins.

1 Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apartado Postal 510-3, Cuernavaca 62250, Morelos, Mexico.
2 Department of Entomology, University of Arizona, Tucson, AZ, USA.

* To whom correspondence should be addressed. E-mail: bravo{at}ibt.unam.mx (A.B.); mario{at}ibt.unam.mx (M.S.)

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