Detection of sixteen genetically modified maize events in processed foods using four event-specific pentaplex PCR systems

A New Reference Plasmid “pGMT27” Provides an Efficient Transgenic Detection Method for Flue-Cured Tobacco

Owing to the economic value of its foliage, tobacco (Nicotiana tabacum) is cultivated all across the world. For the detection of genetically modified (GM) tobacco, there is a lack of universal standard material which ultimately limits the detection methods because the accuracy and comparability of the results cannot be ensured. Here, we prepared a reference plasmid “pGMT27” for the detection of GM tobacco, which was 18,296 bp in length harboring two of the tobacco endogenous and seven exogenous genes. By using qualitative PCR test for the nine genes, 10 copies were used for plasmid sensitivity. In the quantitative real-time PCR (qPCR) assays with pGMT27 as a calibrator, the reaction efficiencies for P-35S and NR were 101.427% and 98.036%, respectively, whereas the limit of detection (LOD) and limit of quantification (LOQ) were 5 copies and 10 copies per reaction. For standard deviation (SD) and relative standard deviation (RSD) of the Ct values, the repeatability values were from 0.04 to 0.42 and from 0.18% to 1.29%, respectively; and the reproducibility values were from 0.04 to 0.39 and from 0.18% to 1.14%, respectively. For the unknown sample test, the average conversion factor (Cf) was 0.39, and the accuracy bias was from −15.55% to 1.93%; for precision, the SD values ranged from 0.02 to 0.62, while RSD values were from 1.34% to 10.6%. We concluded that using the pGMT27 plasmid as a calibrator provided a highly efficient transgenic detection method for flue-cured tobacco.

Development of a Systematic qPCR Array for Screening GM Soybeans

A screening method using the 35S promoter and nos terminator for genetically modified organisms (GMOs) is not sufficient to cover all GM soybean events. In this study, a real-time polymerase chain reaction (also known as quantitative polymerase chain reaction, qPCR) array targeting eight screening assays combined with a prediction system was developed for the rapid tracking of GM soybeans. Each assay’s specificity was tested and confirmed using 17 GM soybean events that have been approved in Korea. The sensitivity of each assay was determined to range from 0.01% to 0.05% using DNA mixtures with different GM ratios, and it was validated by the results of three experimenters. The applicability of this study was tested by monitoring 23 processed foods containing soybeans. It was figured out that 13 of the 23 samples included GM soybeans. The prediction system combined with screening results will be helpful to trace the absence/presence of GM soybean events. This new qPCR array and prediction system for GM soybean detection provides rapid, convenient and reliable results to users.

A 'turn-on' ultra-sensitive multiplex real-time fluorescent quantitative biosensor mediated by a universal primer and probe for the detection of genetically modified organisms

Among the existing multiplex genetically modified organism (GMO) detection methods, significant problems are highlighted, including amplification asymmetry of different targets, and the low detection throughput, which limits their capacity to meet the requirements of high-throughput analysis. To mitigate these challenges, a 'turn-on' ultra-sensitive multiplex real-time fluorescent quantitative biosensor is developed. In this system, the multiplex ligation-dependent amplification (MLPA), universal primer and universal probe are innovatively combined, which can enhanced the amplification specificity, overcome asymmetric amplification and guarantee the homogeneity of amplification efficiency simultaneously. Furthermore, both single and multiplex detection results can be output by the fluorescent group labeled on universal TaqMan probes for different targets in real-time. After optimization, the quantitative detection limit was 5 pg. In conclusion, this strategy could serve as an important tool for GMO detection in processed and commercially available products, even in the fields that require reliable and sensitive detection of DNA targets.

Expression characterization of the herbicide tolerance gene Aryloxyalkanoate Dioxygenase (aad-1) controlled by seven combinations of regulatory elements

BACKGROUND

Availability of well characterized maize regulatory elements for gene expression in a variety of tissues and developmental stages provides effective alternatives for single and multigene transgenic concepts. We studied the expression of the herbicide tolerance gene aryloxyalkanoate dioxygenase (aad-1) driven by seven different regulatory element construct designs including the ubiquitin promoters of maize and rice, the actin promoters of melon and rice, three different versions of the Sugarcane Bacilliform Badnavirus promoters in association with other regulatory elements of gene expression.

RESULTS

Gene expression of aad-1 was characterized at the transcript and protein levels in a collection of maize tissues and developmental stages. Protein activity against its target herbicide was characterized by herbicide dosage response. Although differences in transcript and protein accumulation were observed among the different constructs tested, all events were tolerant to commercially relevant rates of quizalafop-P-ethyl compared to non-traited maize under greenhouse conditions.

DISCUSSION

The data reported demonstrate how different regulatory elements affect transcript and protein accumulation and how these molecular characteristics translate into the level of herbicide tolerance. The level of transcript detected did not reflect the amount of protein quantified in a particular tissue since protein accumulation may be influenced not only by levels of transcript produced but also by translation rate, post-translational regulation mechanisms and protein stability. The amount of AAD-1 enzyme produced with all constructs tested showed sufficient enzymatic activity to detoxify the herbicide and prevent most herbicidal damage at field-relevant levels without having a negative effect on plant health.

CONCLUSIONS

Distinctive profiles of aad-1 transcript and protein accumulation were observed when different regulatory elements were utilized in the constructs under study. The ZmUbi and the SCBV constructs showed the most consistent robust tolerance, while the melon actin construct provided the lowest level of tolerance compared to the other regulatory elements used in this study. These data provide insights into the effects of differing levels of gene expression and how these molecular characteristics translate into the level of herbicide tolerance. Furthermore, these data provide valuable information to optimize future designs of single and multiple gene constructs for maize research and crop improvement.

On-site detection of stacked genetically modified soybean based on event-specific TM-LAMP and a DNAzyme-lateral flow biosensor

Stacked genetically modified organisms (GMO) are becoming popular for their enhanced production efficiency and improved functional properties, and on-site detection of stacked GMO is an urgent challenge to be solved. In this study, we developed a cascade system combining event-specific tag-labeled multiplex LAMP with a DNAzyme-lateral flow biosensor for reliable detection of stacked events (DP305423× GTS 40-3-2). Three primer sets, both event-specific and soybean species-specific, were newly designed for the tag-labeled multiplex LAMP system. A trident-like lateral flow biosensor displayed amplified products simultaneously without cross contamination, and DNAzyme enhancement improved the sensitivity effectively. After optimization, the limit of detection was approximately 0.1% (w/w) for stacked GM soybean, which is sensitive enough to detect genetically modified content up to a threshold value established by several countries for regulatory compliance. The entire detection process could be shortened to 120min without any large-scale instrumentation. This method may be useful for the in-field detection of DP305423× GTS 40-3-2 soybean on a single kernel basis and on-site screening tests of stacked GM soybean lines and individual parent GM soybean lines in highly processed foods.

Event-specific qualitative and quantitative detection of five genetically modified rice events using a single standard reference molecule

One novel standard reference plasmid, namely pUC-RICE5, was constructed as a positive control and calibrator for event-specific qualitative and quantitative detection of genetically modified (GM) rice (Bt63, Kemingdao1, Kefeng6, Kefeng8, and LLRice62). pUC-RICE5 contained fragments of a rice-specific endogenous reference gene (sucrose phosphate synthase) as well as the five GM rice events. An existing qualitative PCR assay approach was modified using pUC-RICE5 to create a quantitative method with limits of detection correlating to approximately 1-10 copies of rice haploid genomes. In this quantitative PCR assay, the square regression coefficients ranged from 0.993 to 1.000. The standard deviation and relative standard deviation values for repeatability ranged from 0.02 to 0.22 and 0.10% to 0.67%, respectively. The Ministry of Food and Drug Safety (Korea) validated the method and the results suggest it could be used routinely to identify five GM rice events.

Evalution of DNA extraction methods in order to monitor genetically modified materials in soy foodstuffs and feeds commercialised in Turkey by multiplex real-time PCR

BACKGROUND

Soybean is one of the most important biotech crops, widely used as an ingredient in both foodstuffs and feed. DNA extraction methods have been evaluated to detect the presence of genetically modified (GM) materials in soya-containing food and feed products commercialised in Turkey.

RESULTS

All extraction methods performed well for the majority of soya foods and feed products analysed. However, the most successful method varied between different products; the Foodproof, Genespin and the cetyltrimethylammonium bromide (CTAB) methods each produced the highest DNA yield and purity for different soya foodstuffs and feeds. Of the samples tested, 20% were positive for the presence of at least two GM elements (35S/NOS) while 11% contained an additional GM element (35S/NOS/FMV). Of the tested products, animal feeds showed a larger prevalence of GM material (50%) than the soya-containing foodstuffs (13%).

CONCLUSION

The best performing extraction methods proved to be the Foodproof, Genespin and CTAB methods for soya-containing food and feed products. The results obtained herein clearly demonstrate the presence of GM soybean in the Turkish market, and that the Foodproof GMO Screening Kit provides reliable screening of soy-containing food and feed products.

GMO quantification: valuable experience and insights for the future

Cultivation and marketing of genetically modified organisms (GMOs) have been unevenly adopted worldwide. To facilitate international trade and to provide information to consumers, labelling requirements have been set up in many countries. Quantitative real-time polymerase chain reaction (qPCR) is currently the method of choice for detection, identification and quantification of GMOs. This has been critically assessed and the requirements for the method performance have been set. Nevertheless, there are challenges that should still be highlighted, such as measuring the quantity and quality of DNA, and determining the qPCR efficiency, possible sequence mismatches, characteristics of taxon-specific genes and appropriate units of measurement, as these remain potential sources of measurement uncertainty. To overcome these problems and to cope with the continuous increase in the number and variety of GMOs, new approaches are needed. Statistical strategies of quantification have already been proposed and expanded with the development of digital PCR. The first attempts have been made to use new generation sequencing also for quantitative purposes, although accurate quantification of the contents of GMOs using this technology is still a challenge for the future, and especially for mixed samples. New approaches are needed also for the quantification of stacks, and for potential quantification of organisms produced by new plant breeding techniques.