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

Authors: VELLICHIRAMMAL, NEETHA - University Of Nebraska; WANG, HAICHUAN - University Of Nebraska; EYUN, SEONG-IL - University Of Nebraska; MORIYAMA, ETSUKO - University Of Nebraska; Coates, Brad; MILLER, NICHOLAS - University Of Nebraska; SIEGFRIED, BLAIR - University Of Nebraska

Submitted to: BMC Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 7/29/2015
Citation: Vellichirammal, N.N., Wang, H., Eyun, S., Moriyama, E.N., Coates, B.S., Miller, N.J., Siegfried, B.D. 2015. Transcriptional analysis of susceptible and resistant European corn borer strains and their response to Cry1F protoxin. Biomed Central (BMC) Genomics. 16:558. doi: 10.1186/s12864-015-1751-6.

Interpretive Summary: Genetically-engineered (transgenic) crop plants express Bt protein toxins that kill insects that feed upon them. Scientists and crop producers see benefits in these plants because they offer control of insect damage without the harmful environmental effects associated with conventional chemical insecticide use, along with reduced surface and ground water contamination, and improved farm worker safety issues. The European corn borer, is an important pest of corn in the United States, is controlled by transgenic Bt corn. Damage and control costs for this insect exceed $1 billion from an annual crop valued more than $22 billion. A laboratory strain of European corn borer was previous show to be capable of surviving on transgenic corn expressing the Cry1F Bt toxin. In this study USDA and university researchers described the expression of all genes in the midgut of Cry1F resistant and susceptible European corn borer either feeding on Cry1F toxin or non-Bt toxin diets. We demonstrated that gene expression of Cry1F resistant suggests a lack of cellular damage and that this strain is capable of avoiding initial pore formation involved in the Bt toxin mode of action. These findings are important to university and industry stakeholders, and add to scientific understanding of the genetic mechanisms that lead to Bt resistance among insect pests of corn.

Technical Abstract: The development of insect resistance to pesticides and biological toxins expressed by genetically modified crop plants is a serious threat to sustainable agricultural production. One of the central goals of insect resistance management (IRM) is to understand the evolution and adaptation of pest insect species to these control strategies. Understanding the mechanism of Cry1F toxin resistance in European corn borer (ECB) is essential when we try to elucidate the insect resistance to the Bacillus thuringiensis (Bt) toxins in other economically important pests. However, little is known about the global transcriptomic response of ECB to Cry toxins or its mechanism of resistance to the toxin. Most of this uncertainty can be attributed to the limited genomic resources in this pest species. An ECB midgut transcriptome of 36,125 transcripts was assembled de novo from 106 million reads, and used as a reference for estimation of differential gene expression analysis. Evaluation of gene expression profiles from midgut in 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 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. Current study provides a valuable resource for further molecular research in this and related pest species and provides insight on the role of host response to Cry1F toxin in ECB and also into the possible mechanisms of Bt resistance.