Bt Toxin Resistance from Loss of a Putative Carbohydrate-Modifying Enzyme

The development of resistance is the main threat to the long-term use of toxins from Bacillus thuringiensis (Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene, Caenorhabditis elegans bre-5, which encodes a putative beta-1,3-galactosyltransferase. Lack of bre-5 in the intestine led to resistance to the Bt toxin Cry5B. Wild-type but not bre-5 mutant animals were found to uptake toxin into their gut cells, consistent with bre-5 mutants lacking toxin-binding sites on their apical gut. bre-5 mutants displayed resistance to Cry14A, a Bt toxin lethal to both nematodes and insects; this indicates that resistance by loss of carbohydrate modification is relevant to multiple Bt toxins.