Three cadherin alleles associated with resistance to Bacillus thuringiensis in pink bollworm

Abstract

Evolution of resistance by pests is the main threat to long-term insect control by transgenic crops that produce Bacillus thuringiensis (Bt) toxins. Because inheritance of resistance to the Bt toxins in transgenic crops is typically recessive, DNA-based screening for resistance alleles in heterozygotes is potentially much more efficient than detection of resistant homozygotes with bioassays. Such screening, however, requires knowledge of the resistance alleles in field populations of pests that are associated with survival on Bt crops. Here we report that field populations of pink bollworm (Pectinophora gossypiella), a major cotton pest, harbored three mutant alleles of a cadherinencoding gene linked with resistance to Bt toxin Cry1Ac and survival on transgenic Bt cotton. Each of the three resistance alleles has a deletion expected to eliminate at least eight amino acids upstream of the putative toxin-binding region of the cadherin protein. Larvae with two resistance alleles in any combination were resistant, whereas those with one or none were susceptible to Cry1Ac. Together with previous evidence, the results reported here identify the cadherin gene as a leading target for DNA-based screening of resistance to Bt crops in lepidopteran pests.

Sequence variation in the cadherin gene of Ostrinia nubilalis: a tool for field monitoring

“…Resistant allele r2 had a truncation deletion that eliminated homologous P. gossypiella TBR1 ( 862 DNVINIVDINNK 873 ) and TBR2 ( 1341 PLPGSLLTVTVT 1352 ); and allele r1 had a nonsynonymous change directly flanking TBR1 (R 861 ) compared to of susceptible and r3 alleles (G 861 ). Morin et al (2003) also established a correlation between cadherin resistance alleles and increased P. gossypiella larval weight among individuals from a Texas field sample (TX-01) reared on diet containing 1 mg Cry1Ac/ ml. Recessive Bt resistant alleles were independently selected for in P. gossypiella strain APHIS-98R (Tabashnik et al, 2004), suggesting utility of fielding surveillance to monitor the development of resistance.…”

“…Three cadherin alleles (r1, r2, and r3) in Cry1Ac resistant P. gossypiella strain AZP-R differed by block deletion or truncation (Morin et al, 2003), and shared no fixed peptide sequence differences compared to alleles from a susceptible line. Resistant allele r2 had a truncation deletion that eliminated homologous P. gossypiella TBR1 ( 862 DNVINIVDINNK 873 ) and TBR2 ( 1341 PLPGSLLTVTVT 1352 ); and allele r1 had a nonsynonymous change directly flanking TBR1 (R 861 ) compared to of susceptible and r3 alleles (G 861 ).…”

“…Molecular assays have been developed to detect resistance genes in insect populations (Steichen and Ffrench-Constant, 1994;Field et al, 1996), and screening known resistance alleles in P. gossypiella may show promise for population surveillance (Morin et al, 2003;Tabashnik et al, 2004). In a preliminary surveillance experiment we used PCR-RFLP to estimate frequencies of O. nubilalis cadherin alleles (SNP haplotypes) in a population of susceptible adults collected near Mead, Nebraska.…”

“…A Manduca sexta 210-kDa E-cadherin-like peptide bound activated (trypsinized) Cry1A toxin (Francis and Bulla, 1997). Midgut expressed cadherinlike cDNAs were isolated from M. sexta (Vadlamudi et al, 1995), Bombyx mori (Nagamatsu et al, 1998a), Heliothis virescens (Gahan et al, 2001), and Pectinophora gossypiella (Morin et al, 2003). Furthermore, a cadherin knockout from a transposon insertion resulted in 40,000-fold resistance in the H. virescens YHD2 colony (Gahan et al, 2001).…”

“…Furthermore, a cadherin knockout from a transposon insertion resulted in 40,000-fold resistance in the H. virescens YHD2 colony (Gahan et al, 2001). Segregation of alleles at a cadherin locus was associated with resistance in P. gossypiella strain AZP-R (Morin et al, 2003). CRY1A domain II binds lepidopteran midgut epithelial receptors (de Maagd et al, 2001) by interacting with two cadherin motifs (Gomez et al, 2003).…”