Single amino acid mutation in an ATP-binding cassette transporter gene causes resistance to Bt toxin Cry1Ab in the silkworm, Bombyx mori

Abstract

Bt toxins derived from the arthropod bacterial pathogen Bacillus thuringiensis are widely used for insect control as insecticides or in transgenic crops. Bt resistance has been found in field populations of several lepidopteran pests and in laboratory strains selected with Bt toxin. Widespread planting of crops expressing Bt toxins has raised concerns about the potential increase of resistance mutations in targeted insects. By using Bombyx mori as a model, we identified a candidate gene for a recessive form of resistance to Cry1Ab toxin on chromosome 15 by positional cloning. BGIBMGA007792-93 , which encodes an ATP-binding cassette transporter similar to human multidrug resistance protein 4 and orthologous to genes associated with recessive resistance to Cry1Ac in Heliothis virescens and two other lepidopteran species, was expressed in the midgut. Sequences of 10 susceptible and seven resistant silkworm strains revealed a common tyrosine insertion in an outer loop of the predicted transmembrane structure of resistant alleles. We confirmed the role of this ATP-binding cassette transporter gene in Bt resistance by converting a resistant silkworm strain into a susceptible one by using germline transformation. This study represents a direct demonstration of Bt resistance gene function in insects with the use of transgenesis.

Sodium Solute Symporter and Cadherin Proteins Act as Bacillus thuringiensis Cry3Ba Toxin Functional Receptors in Tribolium castaneum

“…Very recently, the functionality for ATP-binding cassette transporter subfamily C member 2 (ABCC2) as Cry1 toxin receptor has been reported in Bombyx mori larvae (5), in accord with the role of this protein in the mechanism of Cry1 toxin resistance (41,42). Remarkably, B. mori ABCC2 protein (42) structurally resembles TcSSS protein in that both are multimembrane-spanning transporters (Fig.…”

“…Remarkably, B. mori ABCC2 protein (42) structurally resembles TcSSS protein in that both are multimembrane-spanning transporters (Fig. 5).…”

Neo-sex chromosomes and adaptive potential in tortricid pests

“…Although ABCC2 mutations are reported to be recessive (33)(34)(35), the resistance conferred by insensitive Ace is in most cases semidominant. However, dominance levels of insensitive Ace alleles were shown to vary from recessivity to dominance and correlate with the activity of insensitive Ace forms in mosquito Culex pipiens.…”

“…2 and 3), and presumably in all other species of the tortricid subfamilies Olethreutinae and Tortricinae, which comprise almost 700 economically important pests worldwide (30). Whereas Rdl orthologs conferring resistance to cyclodiene insecticides are also Z-linked in other Lepidoptera (31,32), the Ace-1 and ABCC2 associated with insensitivity to organophosphates and carbamates, and resistance to Bacillus thuringiensis toxin Cry1Ab, respectively, are assignable to the autosomal linkage group corresponding to B. mori chromosome 15 in distantly related species (15,(33)(34)(35). By contrast, in most tortricids, the sex-linkage of these two genes is thus a direct consequence of F(Z;15).…”

Resistance to Bt Crops; Influence, mechanisms and management strategies

“…Bombyx mori resistance to Cry1Ab has been conferred by a single amino acid mutation in ATP-binding cassette transporter gene (Atsumi et al, 2012).…”