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Applied and Environmental Microbiology, November 2007, p. 6939-6944, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.01703-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mutated Cadherin Alleles from a Field Population of Helicoverpa armigera Confer Resistance to Bacillus thuringiensis Toxin Cry1Ac{triangledown}

Yajun Yang, Haiyan Chen,{dagger} Yidong Wu,* Yihua Yang, and Shuwen Wu

Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China

Received 24 July 2007/ Accepted 29 August 2007

The cotton bollworm Helicoverpa armigera is the major insect pest targeted by cotton genetically engineered to produce the Bacillus thuringiensis toxin (transgenic Bt cotton) in the Old World. The evolution of this pest's resistance to B. thuringiensis toxins is the main threat to the long-term effectiveness of transgenic Bt cotton. A deletion mutation allele (r1) of a cadherin gene (Ha_BtR) was previously identified as genetically linked with Cry1Ac resistance in a laboratory-selected strain of H. armigera. Using a biphasic screen strategy, we successfully trapped two new cadherin alleles (r2 and r3) associated with Cry1Ac resistance from a field population of H. armigera collected from the Yellow River cotton area of China in 2005. The r2 and r3 alleles, respectively, were created by inserting the long terminal repeat of a retrotransposon (designated HaRT1) and the intact HaRT1 retrotransposon at the same position in exon 8 of Ha_BtR, which results in a truncated cadherin containing only two ectodomain repeats in the N terminus of Ha_BtR. This is the first time that the B. thuringiensis resistance alleles of a target insect of Bt crops have been successfully detected in the open field. This study also demonstrated that bollworm larvae carrying two resistance alleles can complete development on Bt cotton. The cadherin locus should be an important target for intensive DNA-based screening of field populations of H. armigera.

* Corresponding author. Mailing address: Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China. Phone and fax: 86 25 8439 6062. E-mail: wyd{at}njau.edu.cn

{triangledown} Published ahead of print on 7 September 2007.

{dagger} Present address: Cotton Research Institute, Chinese Academy of Agricultural Sciences, Anyang 455000, China.

Applied and Environmental Microbiology, November 2007, p. 6939-6944, Vol. 73, No. 21
0099-2240/07/$08.00+0     doi:10.1128/AEM.01703-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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