Changes in gene expression in European corn borer larvae (Ostrinia nubilalis) in response to Bacillus thuringiensis Cry1Ab protoxin exposure

The European corn borer (ECB), Ostrinia nubilalis, is the target pest for corn varieties expressing insecticidal toxins from Bacillus thuringiensis (Bt). We developed a cDNA microarray based on 15,000 cDNA elements representing 2,755 unique genes identified from ECB larval gut. This microarray was used to monitor gene expression in early fourth instar Bt-susceptible ECB larvae after 6 h feeding on diet with or without Cry1Ab protoxin. We identified 169 genes from the gut for which the expression was changed more than 2-fold for larvae exposed to Cry1Ab, in which 57 annotated genes were classified based on their molecular functions: 35 genes are involved in catalytic activity, 13 for binding activity, and the remaining genes for other functions. Thirty-six up-regulated transcripts may be involved in insect defense and signaling, and 21 down-regulated genes may have roles in Cry1Ab protoxin activation, and toxin binding processes. Twelve of these genes are potentially involved in Bt toxicity and resistance, which include 7 serine protease, 1 alkaline phosphatase, 3 aminopeptidase, and 1 cadherin-like genes. The expression of serine protease genes was variable (one was up-regulated and six were down-regulated), but the three Bt-binding proteins, aminopeptidase, alkaline phosphatase and cadherin, were down regulated under Cry1Ab protoxin exposure. This study is the first large-scale survey of Cry1Ab protoxin induced transcriptional responses in ECB gut tissue and also provides a platform for functional studies of toxin-insect interactions.