Major putative pesticide receptors, detoxification enzymes, and transcriptional profile of the midgut of the tobacco budworm, Heliothis virescens (Lepidoptera: Noctuidae)

Insecticide resistance mechanisms, including those for Cry proteins (Bt), in Heliothis virescens are not well understood. Sequencing of midgut transcriptomes may facilitate the discovery of the genes responsible for resistance development. In this study, a total of 5856 Sanger sequences were obtained and assembled to 1687 contigs (464) and singletons (1233) with average length of 507 bp. Blast similarity search showed that 1372 cDNAs from this study matched different genes or cDNAs in the GenBank and other sequence databases. Blast2go annotation identified 611 highly similar proteins with metabolic and cellular processes as major biological functions and catalytic activity and binding as major molecular functions. At least 143 contigs and singletons were associated with pesticide activation, detoxification, and resistance development. These cDNAs, with average length of 601 bp, matched nine groups of pesticide resistance related genes. At least 80 cDNAs coded for Bt resistance related enzymes and potential receptors, including 58 proteinases, 4 cadherins, 13 aminopeptidase, and 5 alkaline phosphatases. Other putative detoxification enzymes included 20 cytochrome P450 oxidases, 11 glutathione S-transferases, 9 esterases, 8 sodium channels, and 15 cytochrome oxidases. Of the 143 contigs and singletons, 111 cDNA sequences seemed to be new resistance candidate gene transcripts in GenBank because they either priorly matched resistance candidate cDNAs of other species, or had low sequence identity with those previously sequenced from H. virescens. This study provides a foundation for future research to develop a gut-specific DNA microarray for analysis of the global changes of gene expression in response to biological and chemical pesticides. Future development resistance management strategies could benefit from this study and help continue research to identify key genes targetable by classic and novel approaches.

Sequencing of midgut transcriptomes may facilitate the discovery of the genes responsible for resistance development. In this study, a total of 5856 Sanger sequences were obtained and assembled to 1687 contigs and singletons. At least 143 contigs and singletons were associated with pesticide activation, detoxification, and resistance development. Of the 143 contigs and singletons, 111 cDNA sequences seemed to be new resistance candidate gene transcripts in GenBank.Figure optionsDownload as PowerPoint slideResearch highlights
► Insect midgut contains complex of enzymes.
► Microbial and chemical insecticides firstly and mainly act on midgut.
► This study is to reveal midgut transcriptome profiles.
► To discover new resistance related genes.
► To facilitate strategic resistance management with inhibition and RNAi.