Abstract
We developed a microarray based on 2895 unique transcripts assembled from 15,000 cDNA sequences from the European corn borer (Ostrinia nubilalis) larval gut. This microarray was used to monitor gene expression in early third-instar larvae of Bacillus thuringiensis (Bt)-susceptible O. nubilalis after 6 h feeding on diet, with or without the Bt Cry1Ab protoxin. We identified 174 transcripts, for which the expression was changed more than two-fold in the gut of the larvae fed Cry1Ab protoxin (p < 0.05), representing 80 down-regulated and 94 up-regulated transcripts. Among 174 differentially expressed transcripts, 13 transcripts putatively encode proteins that are potentially involved in Bt toxicity, and these transcripts include eight serine proteases, three aminopeptidases, one alkaline phosphatase, and one cadherin. The expressions of trypsin-like protease and three aminopeptidase transcripts were variable, but two potential Bt-binding proteins, alkaline phosphatase and cadherin were consistently up-regulated in larvae fed Cry1Ab protoxin. The significantly up and down-regulated transcripts may be involved in Cry1Ab toxicity by activation, degradation, toxin binding, and other related cellular responses. This study is a preliminary survey of Cry1Ab protoxin-induced transcriptional responses in O. nubilalis gut and our results are expected to help with further studies on Bt toxin-insect interactions at the molecular level.
Highlights
The European corn borer, Ostrinia nubilalis, which primarily infests corn, is responsible for significant yield losses in North America [1]
We used the artificial diet containing the protoxin at the LC50 concentration (0.25 μg/mL diet) to feed the larvae, the protoxin did not cause any visible effect on the larvae because this LC50 value was determined based on a seven-day bioassay whereas the feeding duration in this study was only six hours
We used a feeding period of six hours since the larvae had stopped their feeding after they ingested the diet containing Cry1Ab protoxin
Summary
The European corn borer, Ostrinia nubilalis, which primarily infests corn, is responsible for significant yield losses in North America [1]. Transgenic corn hybrids, expressing Cry toxins encoded by genes derived from Bacillus thuringiensis (Bt), are one of the most successful technologies for controlling O. nubilalis under field conditions [4,5]. Cry toxins have been effective control agents with insecticidal specificity toward several insect pests in field, like O. nubilalis larvae. These insects have the potential to develop resistance within a few generations if they are continuously exposed to Cry1Ab protoxin [9]. The mechanism of resistance to Bt toxin in insects is multifaceted, mirroring the complicated pore-formation mode of action involving multiple steps and gene products [8,13]. Results from this research are expected to provide a platform for functional studies of toxin-insect interactions
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