Comprehensive analysis of the molecular characterization of GM rice G6H1 using a paired-end sequencing approach

Development and performance evaluation of whole-genome sequencing with paired-end and mate-pair strategies in molecular characterization of GM crops: One GM rice 114-7-2 line as an example

Basic data for the safety assessment of transgenic line involves the molecular characterization of the integration site of exogenous DNA, flanking sequences, copy number, and unintended plasmid backbone residues. However, performing a full molecular characterization remains challenging, especially for GMOs that possess complex exogenous DNA integrations. We established two whole-genome sequencing strategies: paired-end and mate-pair, to characterize the exogenous DNA integration of a human serum albumin gene into rice line 114-7-2, and evaluated the performance of these two strategies in the molecular characterization of transgenic line. The results showed the existence of two exogenous DNA insertion loci (Chr 01 and Chr 04) and their corresponding flanking sequences, five copies of the exogenous rHSA gene, and the presence of unintended residual plasmid backbone sequences. However, the WGS-MP strategy demonstrated higher efficiency, lower cost, and lower background noise compared with the WGS-PE analysis, especially for identification of the exogenous DNA integration site.

A paired-end whole-genome sequencing approach enables comprehensive characterization of transgene integration in rice

Efficient, accurate molecular characterization of genetically modified (GM) organisms is challenging, especially for those transgenic events transferred with genes/elements of recipient species. Herein, we decipher the comprehensive molecular characterization of one novel GM rice event G281 which was transferred with native promoters and an RNA interference (RNAi) expression cassette using paired-end whole genome sequencing (PE-WGS) and modified TranSeq approach. Our results show that transgenes integrate at rice chromosome 3 locus 16,439,674 included a 36 bp deletion of rice genomic DNA, and the whole integration contains two copies of the complete transfer DNA (T-DNA) in a head-to-head arrangement. No unintended insertion or backbone sequence of the transformed plasmid is observed at the whole genome level. Molecular characterization of the G281 event will assist risk assessment and application for a commercial license. In addition, we speculate that our approach could be further used for identifying the transgene integration of cisgenesis/intragenesis crops since both ends of T-DNA in G281 rice were from native gene or elements which is similar with that of cisgenesis/intrasgenesis. Our results from the in silico mimicking cisgenesis event confirm that the mimic rice Gt1 gene insertion and its flanking sequences are successfully identified, demonstrating the applicability of PE-WGS for molecular characterization of cisgenesis/intragenesis crops.

Coupling paired-end whole-genome sequencing with droplet digital PCR enabled precise identification of a transgene insertion in the genetically modified rice event G281 on chromosome 3 and the potential for exploring the native gene integration.

LIFE-Seq: a universal Large Integrated DNA Fragment Enrichment Sequencing strategy for deciphering the transgene integration of genetically modified organisms

Molecular characterization of genetically modified organisms (GMOs) yields basic information on exogenous DNA integration, including integration sites, entire inserted sequences and structures, flanking sequences and copy number, providing key data for biosafety assessment. However, there are few effective methods for deciphering transgene integration, especially for large DNA fragment integration with complex rearrangement, inversion and tandem repeats. Herein, we developed a universal Large Integrated DNA Fragments Enrichment strategy combined with PacBio Sequencing (LIFE-Seq) for deciphering transgene integration in GMOs. Universal tilling DNA probes targeting transgenic elements and exogenous genes facilitate specific enrichment of large inserted DNA fragments associated with transgenes from plant genomes, followed by PacBio sequencing. LIFE-Seq were evaluated using six GM events and four crop species. Target DNA fragments averaging ~6275 bp were enriched and sequenced, generating ~26 352 high fidelity reads for each sample. Transgene integration structures were determined with high repeatability and sensitivity. Compared with next-generation whole-genome sequencing, LIFE-Seq achieved better data integrity and accuracy, greater universality and lower cost, especially for transgenic crops with complex inserted DNA structures. LIFE-Seq could be applied in molecular characterization of transgenic crops and animals, and complex DNA structure analysis in genetics research.

Universal LNA Probe-Mediated Multiplex Droplet Digital Polymerase Chain Reaction for Ultrasensitive and Accurate Quantitative Analysis of Genetically Modified Organisms

Multiplex and high-throughput assays are becoming the main trends in the development of new nucleic acid detection and quantification methods, such as those for genetically modified organism (GMO) analysis. Here, we report a novel universal LNA probe-mediated droplet digital polymerase chain reaction (PCR) method (ULNA-ddPCR) for multiple DNA target quantification in GMOs. In ULNA-ddPCR, only one universal LNA probe is used for multiple DNA targets instead of using one to one TaqMan probe. The specificity, sensitivity, dynamic range, and accuracy of the ULNA-ddPCR method are determined by employing GM rice analysis as an example. Simplex and triplex ULNA-ddPCR assays for three GM rice events, T2A-1, T1C-19, and G6H1, are established and evaluated. All results indicate that the developed simplex and triplex ULNA-ddPCR assays are suitable for quantitative analysis of GM rice events with high sensitivity, accuracy, and low cost. The ULNA-ddPCR method also has the potential for multiple DNA target quantification in other research fields.

Whole-Genome Sequencing: An Effective Strategy for Insertion Information Analysis of Foreign Genes in Transgenic Plants

Molecular characterization is a key step in the risk assessment of genetically modified organisms (GMOs) for regulatory approval. Herein, we describe a method for analyzing copy number, insertion loci, and flanking sequences through whole-genome sequencing (WGS) and bioinformatics. Comprehensive molecular characterization of G2-6 transgenic rice was performed using this pipeline. The results showed that one copy of the foreign gene was inserted into rice chromosome 8. There was no vector backbone insertion but an unexpected insertion and DNA rearrangement at the 3' end of the T-DNA. We also obtained the 5' and 3' flanking sequences of the T-DNA. Our results suggested that the use of a combination of WGS and bioinformatics is an effective strategy for the molecular characterization of GMOs.