An integrated strategy involving high-throughput sequencing to characterize an unknown GM wheat event in Canada.

Abstract

Glyphosate-resistant wheat plants were discovered in southern Alberta in 2017, representing an unauthorized GM release in Canada. The Canadian Food Inspection Agency undertook a series of experiments to characterize and identify this unknown GM wheat, as well as to develop and validate construct-specific and event-specific qPCR assays. Results of PCR-based assays and Sanger sequencing indicated the presence of CaMV 35S promoter (p35S), Rice Actin 1 intron (RactInt1), CP4-EPSPS gene and nopaline synthase terminator (tNOS) elements in the unknown GM wheat. Genome walking and bead capture strategies, combined with high-throughput sequencing, were used to identify the 5' and 3' wheat junctions and the subsequent mapping of the insert to chromosome 3B of the wheat genome. A probable transformation vector, pMON25497, was recognized, and further testing identified the unknown GM wheat as MON71200 event, one of two events obtained with the pMON25497 vector. The two construct-specific assays targeted the junctions of the RactInt1 and the CP4-EPSPS elements and the CP4-EPSPS and tNOS elements, while the event-specific assay was located at the 3' junction into the wheat genome. Both construct-specific and event-specific assays had limits of detection of 0.10% of MON71200 in a seed pool. As expected, the two construct-specific assays cross-reacted with other wheat and corn events containing the same elements in the same order. No cross-reactivity was observed for the event-specific assay. The integrated strategy employed in this study can serve as a model for other cases when facing similar challenges involving unknown GM events.