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Abstract:
Toxins from the bacterium Bacillus thuringiensis (Bt) are used widely for insect control in sprays and
transgenic plants, but their efficacy is reduced when pests evolve resistance. Previous work showed that
mutations in a gene encoding the transporter protein ABCC2 are linked with resistance to Bt toxins Cry1Ab,
Cry1Ac or both in four species of Lepidoptera. Here we compared the ABCC2 gene of Helicoverpa armigera
(HaABCC2) between susceptible strains and a laboratory-selected strain with .1,000-fold resistance to
Cry1Ac relative its susceptible parent strain. We discovered a 73-base pair (bp) insertion in the cDNA of the
resistant strain that generates a premature stop codon expected to yield a truncated ABCC2 protein.
Sequencing of genomicDNArevealed that this insertion is an intron that is not spliced out because of a 6-bp
deletion at its splicing site. Analysis of progeny from crosses revealed tight genetic linkage between
HaABCC2 and resistance to Cry1Ac. These results provide the first evidence that mis-splicing of a gene encoding an ABCC2 protein confers resistance to a Bt toxin.
