Development and Interlaboratory Validation of a Novel Reproducible Qualitative Method for GM Soybeans Using Comparative Cq-Based Analysis for the Revised Non-GMO Labeling System in Japan

Many countries have implemented the labeling system of genetically modified organisms (GMO). In Japan, the regulatory threshold for non-GMO labeling will be revised and restricted to undetectable by April 2023. The practical criterion for the revised system is based on the limit of detection (LOD). However, determining whether the commingling of GMO levels exceeds the LOD is challenging because GM contents close to the LOD are usually below the limit of quantification. In this study, we developed a qualitative method based on comparative Cq-based analysis targeting cauliflower mosaic virus 35S promoter and GM soybean MON89788 event-specific sequences that could be applicable to the revised non-GMO labeling. Delta Cq values between the target and endogenous sequences were calculated, and the Delta Delta Cq value obtained was used as a criterion to determine analytical samples with GM contents exceeding the threshold. To improve the reproducibility of the method, we used a standard plasmid that yields equivalent and stable Delta Cq values comparable with those obtained from LOD samples. The developed method was validated with an interlaboratory study. The new qualitative detection concept would be useful for ensuring robust and reproducible results among laboratories, particularly for detecting low-copy-number DNA samples.

Automated summary

Many countries have implemented labeling systems for genetically modified organisms (GMOs). Japan is revising and restricting the regulatory threshold for non-GMO labeling. A qualitative method based on comparative Cq-based analysis has been developed in this study, which could be useful for the revised non-GMO labeling.