Cadherin repeat 5 mutation associated with Bt resistance in a field-derived strain of pink bollworm

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

doi:10.1038/s41598-020-74102-z

Abstract

Evolution of resistance by pests reduces the benefits of transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Here we analyzed resistance to Bt toxin Cry1Ac in a field-derived strain of pink bollworm (Pectinophora gossypiella), a global pest of cotton. We discovered that the r14 allele of the pink bollworm cadherin gene (PgCad1) has a 234-bp insertion in exon 12 encoding a mutant PgCad1 protein that lacks 36 amino acids in cadherin repeat 5 (CR5). A strain homozygous for this allele had 237-fold resistance to Cry1Ac, 1.8-fold cross-resistance to Cry2Ab, and developed from neonate to adult on Bt cotton producing Cry1Ac. Inheritance of resistance to Cry1Ac was recessive and tightly linked with r14. PgCad1 transcript abundance in midgut tissues did not differ between resistant and susceptible larvae. Toxicity of Cry1Ac to transformed insect cells was lower for cells expressing r14 than for cells expressing wild-type PgCad1. Wild-type PgCad1 was transported to the cell membrane, whereas PgCad1 produced by r14 was not. In larval midgut tissue, PgCad1 protein occurred primarily on the brush border membrane only in susceptible larvae. The results imply r14 mediates pink bollworm resistance to Cry1Ac by reduced translation, increased degradation, and/or mislocalization of cadherin.

Highlights

Evolution of resistance by pests reduces the benefits of transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt)
We discovered that r14 has a 234-bp insertion in exon 12 predicted to cause the absence of 36 amino acids in the cadherin repeat 5 (CR5) of PgCad[1] protein
Sequencing of PgCad[1] cDNA revealed the r14 allele from Cry1Ac-resistant strain AQ189 has a deletion of 108 bases (1783 to 1890) (Fig. 1), encoding a PgCad[1] protein that lacks 36 amino acids in CR5, which corresponds with the amino acids encoded by exon 12 (Figs. 1 and S1)

Summary

Introduction

Evolution of resistance by pests reduces the benefits of transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). We analyzed resistance to Bt toxin Cry1Ac in a fieldderived strain of pink bollworm (Pectinophora gossypiella), a global pest of cotton. We focus on resistance to Bt toxin Cry1Ac associated with a novel allele (r14) of the cadherin gene PgCad[1] in the pink bollworm, Pectinophora gossypiella, a global cotton p est[19,20]. Populations in China remain susceptible to the Cry1Ac-producing cotton grown t here[13,21,22] These different outcomes are consistent with the idea that refuges of non-Bt cotton delayed resistance in China and the United States, but were scarce or absent in India[13]

Methods

Results

Conclusion