Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2005
Publication Date: February 1, 2006
Citation: Coates, B.S., Hellmich II, R.L., Lewis, L.C. 2006. Sequence variation in trypsin- and chymotrypsin-like cDNAs from the midgut of Ostrinia nubilalis: methods for allelic differentiation of candidate Bacillus thuringiensis resistance genes. Insect Molecular Biology. 15(1):13-24. Interpretive Summary: Several types of genetically-engineered (transgenic) plants have been produced that kill insects when they feed. Scientists and crop producers are excited about these plants because they offer an effective way to kill pests without conventional chemical insecticides. Reduced chemical usage translates into less surface and ground water contamination. Transgenic corn controls the European corn borer, an important pest of corn in the United States. 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 Bacillus thuringiensis (Bt) transgenic corn, however, has many scientists concerned that this pest could become resistant. In this study, three trypsin and two chymotrypsin genes were isolated, of which one trypsin previously was shown to be involved in resistance to commercial Bt sprays. This and the remaining genes also may be involved in potential insect resistance to Bt corn. This research provides a molecular tool for determining involvement of these genes in Bt resistance mechanisms. 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: Midgut expressed alkaline serine proteases of Lepidoptera function in conversion of Bacillus thuringiensis (Bt) protoxin to active toxin, and reduced levels of transcript T23 is associated with Ostrinia nubilalis resistance to Dipel (TM) Bt formulations. Three groups of trypsin- (OnT25, OnT23, and OnT3) and two chymotrypsin-like (OnC1 and OnC2) cDNAs were isolated from O. nubilalis midgut tissue. Intraspecific groupings are based on cDNA similarity and peptide phylogeny. Derived serine proteases showed a catalytic triad (His, Asp, and Ser; except transcript OnT23a), three substrate specificity-determining residues, and three paired disulfide bonds. RT-PCR indicated all transcripts are expressed in the midgut. Mendelian-inherited genomic markers for loci OnT23, OnT3, and OnC1 will be useful for association of alleles with bioassayed Bt toxin resistance phenotypes.