Abstract
BackgroundAsian corn borer (ACB), Ostrinia furnacalis (Guenée), is the major insect pest of maize in China and countries of East and Southeast Asia, the Pacific and Australasia. ACB can develop strong resistance to the transgenic Bt maize expressing Cry1Ab, the most widely commercialized Bt maize worldwide. However, the molecular basis for the resistance mechanisms of ACB to Cry1Ab remained unclear. Two biological replicates of the transcriptome of Bt susceptible (ACB-BtS) and Cry1Ab resistant (ACB-AbR) strains of ACB were sequenced using Solexa/Illumina RNA-Seq technology to identify Cry1Ab resistance-relevant genes.ResultsThe numbers of unigenes for two biological replications were 63,032 and 53,710 for ACB-BtS and 57,770 and 54,468 for ACB-AbR. There were 35,723 annotated unigenes from ACB reads found by BLAST searching NCBI non-redundant, NCBI non-redundant nucleotide, Swiss-prot protein, Kyoto Encyclopedia of Genes and Genomes, Cluster of Orthologous Groups of proteins, and Gene Ontology databases. Based on the NOISeq method, 3,793 unigenes were judged to be differentially expressed between ACB-BtS and ACB-AbR. Cry1Ab resistance appeared to be associated with change in the transcription level of enzymes involved in growth regulation, detoxification and metabolic/catabolic process. Among previously described Bt toxin receptors, the differentially expressed unigenes associated with aminopeptidase N and chymotrypsin/trypsin were up-regulated in ACB-AbR. Whereas, other putative Cry receptors, cadherin-like protein, alkaline phosphatase, glycolipid, actin, V-type proton ATPase vatalytic, heat shock protein, were under-transcripted. Finally, GPI-anchor biosynthesis was found to be involved in the significantly enriched pathway, and all genes mapped to the pathway were substantially down-regulated in ACB-AbR.ConclusionTo our knowledge, this is the first comparative transcriptome study to discover candidate genes involved in ACB Bt resistance. This study identified differentially expressed unigenes related to general Bt resistance in ACB. The assembled, annotated transcriptomes provides a valuable genomic resource for further understanding of the molecular basis of ACB Bt resistance mechanisms.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1362-2) contains supplementary material, which is available to authorized users.
Highlights
Asian corn borer (ACB), Ostrinia furnacalis (Guenée), is the major insect pest of maize in China and countries of East and Southeast Asia, the Pacific and Australasia
Annotation of assembled unigenes A total of 61,622 unigenes were detected from the four ACB libraries, among them, 35,723 unique sequences were annotated based on blastx alignment (E-value < 0.00001) searches of six public databases: NCBI nonredundant (NR), NCBI non-redundant nucleotide (NT), Swiss-prot protein, Kyoto Encyclopedia of Genes and Genomes (KEGG), Cluster of Orthologous Groups of proteins (COG), and Gene Ontology (GO) databases (Additional file 3: Table S1)
Similar dominance of catalytic genes was observed in the midgut transcriptome of D. saccharalis [54], H. virescens [55] and P. xylostlla [31]. The majority of these differentially expressed unigenes (DEUs) (85.8%) were down-regulated in ACB-AbR, unlike the discovery in P. xylostlla, in which majority of the DEUs were up-regulated in Cry1Ac resistant stain [31]. These findings suggested that the mechanism of Cry1Ab resistance in ACB might differ from that in P. xylostlla, or the up-regulated expression of the minority unigenescould be compensating for the lose of the other catalytic genes to minimize the fitness costs of the resistance
Summary
Asian corn borer (ACB), Ostrinia furnacalis (Guenée), is the major insect pest of maize in China and countries of East and Southeast Asia, the Pacific and Australasia. ACB can develop strong resistance to the transgenic Bt maize expressing Cry1Ab, the most widely commercialized Bt maize worldwide. The molecular basis for the resistance mechanisms of ACB to Cry1Ab remained unclear. Two biological replicates of the transcriptome of Bt susceptible (ACB-BtS) and Cry1Ab resistant (ACB-AbR) strains of ACB were sequenced using Solexa/Illumina RNA-Seq technology to identify Cry1Ab resistance-relevant genes
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