Alternative splicing and highly variable cadherin transcripts associated with field-evolved resistance of pink bollworm to bt cotton in India.
Evolution of resistance by insect pests can reduce the benefits of insecticidal proteins from Bacillus thuringiensis (Bt) that are used extensively in sprays and transgenic crops. Despite considerable knowledge of the genes conferring insect resistance to Bt toxins in laboratory-selected strains and in field populations exposed to Bt sprays, understanding of the genetic basis of field-evolved resistance to Bt crops remains limited. In particular, previous work has not identified the genes conferring resistance in any cases where field-evolved resistance has reduced the efficacy of a Bt crop. Here we report that mutations in a gene encoding a cadherin protein that binds Bt toxin Cry1Ac are associated with field-evolved resistance of pink bollworm (Pectinophora gossypiella) in India to Cry1Ac produced by transgenic cotton. We conducted laboratory bioassays that confirmed previously reported resistance to Cry1Ac in pink bollworm from the state of Gujarat, where Bt cotton producing Cry1Ac has been grown extensively. Analysis of DNA from 436 pink bollworm from seven populations in India detected none of the four cadherin resistance alleles previously reported to be linked with resistance to Cry1Ac in laboratory-selected strains of pink bollworm from Arizona. However, DNA sequencing of pink bollworm derived from resistant and susceptible field populations in India revealed eight novel, severely disrupted cadherin alleles associated with resistance to Cry1Ac. For these eight alleles, analysis of complementary DNA (cDNA) revealed a total of 19 transcript isoforms, each containing a premature stop codon, a deletion of at least 99 base pairs, or both. Seven of the eight disrupted alleles each produced two or more different transcript isoforms, which implicates alternative splicing of messenger RNA (mRNA). This represents the first example of alternative splicing associated with field-evolved resistance that reduced the efficacy of a Bt crop.
U.S. Department of Agriculture, Agricultural Research Service, U.S. Arid Land Agricultural Research Center, Maricopa, Arizona, United States of America.
Jeffrey A
JA
Fabrick
National Institute of Plant Health Management, Rajendranagar, Hyderabad, Andhra Pradesh, India.
Jeyakumar
J
Ponnuraj
National Centre for Integrated Pest Management, Indian Agricultural Research Institute, New Delhi, Delhi, India.
Amar
A
Singh
National Centre for Integrated Pest Management, Indian Agricultural Research Institute, New Delhi, Delhi, India.
Raj K
RK
Tanwar
Department of Entomology, University of Arizona, Tucson, Arizona, United States of America.
Gopalan C
GC
Unnithan
Department of Entomology, University of Arizona, Tucson, Arizona, United States of America.
Alex J
AJ
Yelich
Department of Entomology, University of Arizona, Tucson, Arizona, United States of America.
Xianchun
X
Li
Department of Entomology, University of Arizona, Tucson, Arizona, United States of America.
Yves
Y
Carrière
Department of Entomology, University of Arizona, Tucson, Arizona, United States of America.
Bruce E
BE
Tabashnik
D000483:Alleles; D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000494:pharmacology*; D001483:Base Sequence; D005075:Biological Evolution; D015820:Cadherins / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics; D004731:Endotoxins / Q000494:pharmacology*; D003368:Gossypium / Q000469:parasitology*; D006460:Hemolysin Proteins / Q000494:pharmacology*; D007194:India; D007305:Insecticide Resistance / Q000235:genetics*; D008969:Molecular Sequence Data; D009036:Moths / Q000187:drug effects* / Q000235:genetics; D030821:Plants, Genetically Modified / Q000469:parasitology; D017422:Sequence Analysis, DNA
D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D015820:Cadherins; D018076:DNA, Complementary; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis