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Title: Unlinked genetic loci control the reduced transcription of aminopeptidase N 1 and 3 in the European corn borer and determine tolerance to Bacillus thuringiensis Cry1Ab toxin

item Coates, Brad
item SUMERFORD, DOUGLAS - Former ARS Employee
item SIEGFRIED, BLAIR - University Of Nebraska
item Hellmich Ii, Richard
item Abel, Craig

Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2013
Publication Date: 12/1/2013
Citation: Coates, B.S., Sumerford, D.V., Hellmich II, R.L., Abel, C.A. 2013. Unlinked genetic loci control the reduced transcription of aminopeptidase N 1 and 3 in the European corn borer and determine tolerance to Bacillus thuringiensis Cry1Ab toxin. Journal of Insect Biochemistry and Molecular Biology. 43(12):1152-1160.

Interpretive Summary: Genetically-engineered (transgenic) crop plants express 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 and is controlled by transgenic Bacillus thuringiensis (Bt) corn. Damage and control costs for this insect exceed $1 billion from an annual crop valued at more than $22 billion. Nearly complete control of European corn borer on Bt transgenic corn has many scientists concerned that this pest may become resistant to these plants. In this study we show that lack of aminopeptidase N gene expression is involved in determining Cry1Ab toxin resistance traits in the European corn borer. Despite this association, the expression of this aminopeptidase N appears to be controlled by another factor located elsewhere in the European corn borer genome, and is a new mechanism of resistance evolution not previously known by scientists. The outcomes of this research provide stakeholders a molecular tool for characterization of possible resistance genes. The genetics of insect resistance will be useful for all stakeholders interested in finding novel ways to control European corn borers and sustain Bt technology.

Technical Abstract: Crystalline (Cry) toxins from Bacillus thuringiensis (Bt) control insect feeding damage on crop plants via foliar applications or by expression within transgenic plants, but continued Bt use is threatened by the buildup of insect resistance traits. Aminopeptidase N (apn) gene family members encode midgut-expressed membrane-bound digestive enzymes in larval Lepidoptera that also act as receptors for Cry toxin binding. In this study, we used individuals from an Ostrinia nubilalis colony that show an approximately 1400-fold increase in Cry1Ab toxin tolerance to model the inheritance of Bt resistance traits. Comparative real-time polymerase chain reaction (RT-PCR) indicated that transcripts from the apn1 locus are suppressed approximately 146.2-17.3-fold within the midgut of Cry1Ab resistant compared to susceptible larvae. Despite a perfect correlation between apn1 transcript level and inheritance of Cry1Ab resistance, the apn1 locus segregated independently of corresponding apn1 transcription levels. Off-target effects of the molecular markers and mutations acting within the same DNA strand were shown not to influence these results. Evidence suggests that modification of one or more trans-regulatory factors results in suppression of O. nubilalis apn1 gene transcription, and thereby gives rise to a paradigm shift in how Bt resistance traits may be inherited.