Pink Bollworm Resistance to Bt Toxin Cry1Ac Associated with an Insertion in Cadherin Exon 20.

Ling Wang,Peng Wan,Kongming Wu,Xueqin Guo,Dong Xu,Yuemin Ma,Yutao Xiao,Xianchun Li,Kaiyu Liu,Bruce Tabashnik,Shengbo Cong,Jintao Wang

doi:10.3390/toxins11040186

Abstract

Insecticidal proteins from Bacillus thuringiensis (Bt) are widely used to control insect pests, but their efficacy is reduced when pests evolve resistance. We report on a novel allele (r16) of the cadherin gene (PgCad1) in pink bollworm (Pectinophora gossypiella) associated with resistance to Bt toxin Cry1Ac, which is produced by transgenic cotton. The r16 allele isolated from a field population in China has 1545 base pairs of a degenerate transposon inserted in exon 20 of PgCad1, which generates a mis-spliced transcript containing a premature stop codon. A strain homozygous for r16 had 300-fold resistance to Cry1Ac, 2.6-fold cross-resistance to Cry2Ab, and completed its life cycle on transgenic Bt cotton producing Cry1Ac. Inheritance of Cry1Ac resistance was recessive and tightly linked with r16. Compared with transfected insect cells expressing wild-type PgCad1, cells expressing r16 were less susceptible to Cry1Ac. Recombinant cadherin protein was transported to the cell membrane in cells transfected with the wild-type PgCad1 allele, but not in cells transfected with r16. Cadherin occurred on brush border membrane vesicles (BBMVs) in the midgut of susceptible larvae, but not resistant larvae. These results imply that the r16 allele mediates Cry1Ac resistance in pink bollworm by interfering with the localization of cadherin.

Highlights

Engineered crops producing insecticidal proteins from Bacillus thuringiensis (Bt) were cultivated on a cumulative total of over 930 million hectares worldwide from 1996 to 2017 [1]
Survival of the F1 larvae fed on a diet with a concentration of 10 μg Cry1Ac per mL
Resistance to Cry1Ac in previously studied strains of pink bollworm is associated with recessive mutations affecting cadherin [19,22,23,24] and the results described above suggested that male #65 carried a recessive cadherin resistance allele other than r1

Summary

Introduction

Engineered crops producing insecticidal proteins from Bacillus thuringiensis (Bt) were cultivated on a cumulative total of over 930 million hectares worldwide from 1996 to 2017 [1]. Toxins 2019, 11, 186 crops kill some key pests while decreasing reliance on conventional insecticide treatments and reducing harm to non-target species including arthropod natural enemies and vertebrates [2,3,4,5]. These benefits are diminished when pests evolve resistance [6,7,8,9]. Insect resistance to Cry toxins is often associated with mutations affecting one of four types of midgut receptor proteins: cadherin, ATP-binding cassette (ABC) transporters, aminopeptidase N, and alkaline phosphatase [10,11,12,13]

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Conclusion