A sensitive detection method for genetically modified MaisGard™ corn using a nested PCR-system

The genetically modified corn 'MaisGard(TM)' (Monsanto, 'YieldGard(TM)' in the U.S.A.) is resistant to the European corn borer due to the insertion and expression of the cryIA(b) gene from Bacillus thuringiensis ssp. kurstaki. This gene controlled by a 35S promoter from the cauliflower mosaic virus is flanked at its 5'-site by the corn-specific intron 1 of heat shock protein 70 (hsp 70). MaisGard(TM) corn is already widely cultivated in the U.S.A. and may find its way to Europe as a component of a variety of food- and feedstuffs. This work describes the development and evaluation of a sensitive and specific detection method for MaisGard(TM) corn using a nested polymerase chain reaction (PCR) system. The system consists of an outer 401 bp fragment spanning the region of the 35S-promoter to the hsp70 intron 1, and an inner 149 bp fragment. The method was developed using a gradient cycler to empirically determine the range and limits of annealing temperatures that can be used. The sensitivity of the method is 50 pg DNA when using pure transgenic DNA, and 500 ng DNA when 0.01% of the analysed DNA is transgenic. No other tested transgenic corn, including Bt176 and Bt11 from Novartis and 'LibertyLink(TM)' (T25) from AgrEvo or conventional corn could be detected with the MaisGard(TM)-system, indicating the high specificity of the method for MaisGard(TM).