Simple, precise, and less-biased GMO quantification by multiplexed genetic element-specific digital PCR.

BACKGROUND To provide the consumer with choices of GMO or non-GMO, official food labeling systems were established in many countries. Because the threshold GMO content values were set to distinguish between "non-GMO" and "GMO" designations, GMO content quantification method are required for ensuring the appropriateness of labeling. OBJECTIVE As the number of GMOs is continuously increasing around the world, we set out to develop a low-cost, simple and less-biased analytical strategy to cover all necessary detection targets. METHODS Digital PCR methods are advantageous compared to the conventional quantitative real-time PCR methods. We developed a digital PCR-based GMO quantification method to evaluate the GMO content in maize grains. To minimize the analytical workload, we adopted multiplex digital PCR targeting 35S promoter and NOS terminator, which are genetic elements commonly introduced in many GMOs. RESULTS Our method is significantly simpler and more precise than the conventional real-time PCR-based methods. Additionally, we found that this method enables to quantify the copy number of GM DNA without double counting multiple elements (P35S and TNOS) tandemly placed in a recombinant DNA construct. CONCLUSION This is the first report on the development of a GM maize quantification method using the multiplexed genetic element-specific digital PCR method. The tandem effect we report here is quite useful for reducing the bias in the analytical results. HIGHLIGHTS Multiplexed genetic element-specific digital PCR can simplify weight-based GMO quantification and thus should prove useful in light of the continuous increase in the numbers of GM events.