Transcriptional analysis of susceptible and resistant European corn borer strains and their response to Cry1F protoxin

Abstract

BackgroundDespite a number of recent reports of insect resistance to transgenic crops expressing insecticidal toxins from Bacillus thuringiensis (Bt), little is known about the mechanism of resistance to these toxins. The purpose of this study is to identify genes associated with the mechanism of Cry1F toxin resistance in European corn borer (Ostrinia nubilalis Hübner). For this, we compared the global transcriptomic response of laboratory selected resistant and susceptible O. nubilalis strain to Cry1F toxin. We further identified constitutive transcriptional differences between the two strains.ResultsAn O. nubilalis midgut transcriptome of 36,125 transcripts was assembled de novo from 106 million Illumina HiSeq and Roche 454 reads and used as a reference for estimation of differential gene expression analysis. Evaluation of gene expression profiles of midgut tissues from the Cry1F susceptible and resistant strains after toxin exposure identified a suite of genes that responded to the toxin in the susceptible strain (n = 1,654), but almost 20-fold fewer in the resistant strain (n = 84). A total of 5,455 midgut transcripts showed significant constitutive expression differences between Cry1F susceptible and resistant strains. Transcripts coding for previously identified Cry toxin receptors, cadherin and alkaline phosphatase and proteases were also differentially expressed in the midgut of the susceptible and resistant strains.ConclusionsOur current study provides a valuable resource for further molecular characterization of Bt resistance and insect response to Cry1F toxin in O. nubilalis and other pest species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1751-6) contains supplementary material, which is available to authorized users.

Patterns of Gene Expression in Western Corn Rootworm (Diabrotica virgifera virgifera) Neonates, Challenged with Cry34Ab1, Cry35Ab1 and Cry34/35Ab1, Based on Next-Generation Sequencing

“…Like other stressors, the Bt toxins induced changes in WCR gene expression [17,27,28,29]. However, the number of genes altered and GO terms enriched vary greatly with the source of challenge and target organism [16,17,24,28,30], exposure time [18], and even within different populations of the same species.…”

microRNA profiling between Bacillus thuringiensis Cry1Ab‐susceptible and ‐resistant European corn borer, Ostrinia nubilalis (Hübner)

“…Counterparts within each miRNA family were denoted by additional designations behind the underscore (eg onu‐bantam and onu‐bantam_1). Additionally, 29 novel miRNAs, including 27 mature sequences and two star sequences, were predicted based on a previously assembled O. nubilalis midgut transcriptome (Vellichirammal et al ., ) using mi RD eep 2 (Supporting Information Table S1). The predicted precursor structures for onu‐novel‐17 and onu‐novel‐22 appear to have an unbifurcated hairpin structure, low folding energy and miRNA‐miRNA* duplex (*indicates the guide miRNA strand) with 3′ overhangs, which conform to the typical characteristics of miRNA precursors (Fig.…”

“…Putative miRNA targets were predicted using the 3′‐UTRs of 36 125 isoforms within the reference O. nubilalis midgut transcriptome (Vellichirammal et al ., ). Specifically, the CDS was predicted using T rans D ecoder (https://transdecoder.github.io/), and nucleotide regions downstream of putative translational stop sites (TAA, TAG or TGA) were excised using the above in‐house PERL script.…”

“…The biogenesis of miRNAs occurs from a characteristic hairpin structure in the pre‐miRNA, which can be used to predict novel miRNAs that are not represented within existing miRNA families in miRBase. The software mi RD eep 2 (Friedländer et al ., ) was used to identify putative pre‐miRNAs by predicting secondary structures formed amongst transcripts from a previously constructed O. nubilalis midgut transcriptome (Vellichirammal et al ., ), which was considered a valid approach as a proportion of these transcripts received no annotation (eg putative ncRNAs). The trimmed small RNA reads that did not map to miRBase accessions but mapped to ncRNAs within the transcriptome reference using B owtie 2 as described above were considered putatively novel miRNAs.…”

Fitness costs associated with Cry1F resistance in the European corn borer

“…Additionally, the number of genes constitutively differentially expressed between introgressed Cry1F‐resistant and Cry1F‐susceptible O. nubilalis fed on artificial diet are large in number, with 2 660 genes up‐regulated and 2 795 genes down‐regulated (Vellichirammal et al. ). Any analogous gene expression differences between Cry1F‐resistant and Cry1F‐susceptible individuals reared on different maize lines also remains unknown, but may have influenced the fitness costs observed in the current study.…”