Engineering Modified Bt Toxins to Counter Insect Resistance
November 9, 2007| |
Evolution of insect resistance threatens the effectiveness of Bacillus thuringiensis (Bt) toxins that are widely used in sprays and transgenic crops. Previous researches showed that resistance of some insects to Bt proteins is caused by mutations that disrupt a toxin-binding cadherin (proteins necessary for cell to cell adhesion). Bt toxins bind to cadherin in a lock and key fashion. Upon binding, an enzyme removes portions of the bound toxins. The trimmed toxin molecules clump and form pores in the gut membrane cells, causing entry and exit of substances within the cell and ultimately cell death.
Using RNA interference, scientists from the University of Arizona and Universidad Nacional Autónoma de México confirmed the cadherin’s role in Bt toxicity. Tobacco hornworm larvae with silenced cadherin gene showed reduced susceptibility to the Bt toxin Cry1A. The scientists then changed the structure of the Cry1A toxin by deleting one alpha chain from the protein. The modified Cry1A killed cadherin-silenced tobacco hornworms as well as the Bt resistant pink bollworm. The modified Bt toxins may be useful against pests resistant to standard Bt toxins.
The paper published by Science is available to subcribers at http://www.sciencemag.org/cgi/rapidpdf/1146453.pdf. Non subscribers can read the abstract at http://www.sciencemag.org/cgi/content/abstract/1146453
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