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 to xins from Bacillus thuringiensis (Bt) in transgenic plants. Here we report the cloning of a Bt toxin resistance gene, Caenorhabditis elegans bre-5, wh ich encodes a putative beta -1,3-galactosyltransferase. Lack of bre-5 in th e 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, consisten t 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 nematode s and insects; this indicates that resistance by loss of carbohydrate modif ication is relevant to multiple Bt toxins.