Mutations in a novel cadherin gene associated with Bt resistance inHelicoverpa zea

Abstract

20Transgenic corn and cotton produce crystalline (Cry) proteins derived from the soil 21 bacterium Bacillus thuringiensis (Bt) that are toxic to lepidopteran larvae. Helicoverpa zea, a 22 key pest of corn and cotton in the U.S., has evolved widespread resistance to these proteins 23 produced in Bt corn and cotton. While the genomic targets of Cry selection and the mutations 24 that produce resistant phenotypes are known in other lepidopteran species, little is known about 25 how Cry proteins shape the genome of H. zea. We scanned the genomes of Cry1Ac-selected and 26 unselected H. zea lines, and identified eleven genes on six scaffolds that showed evidence of 27 selection by Cry1Ac, including cadherin-86C (cad-86C), a gene from a family that is involved in 28 Cry1A resistance in other lepidopterans. Although this gene was expressed in the H. zea larval 29 midgut, the protein it encodes has only 17 to 22% identity with cadherin proteins from other 30 species previously reported to be involved in Bt resistance. An analysis of midgut-expressed 31 cDNAs showed significant between-line differences in the frequencies of putative 32 nonsynonymous substitutions (both SNPs and indels). Our results indicate that cad-86C is a 33 target of Cry1Ac selection in H. zea. Future work should investigate phenotypic effects of these 34 nonsynonymous substitutions and their impact on phenotypic resistance in field populations.