Investigation of the use of rolling circle amplification for the detection of GM food

GMOIT: a tool for effective screening of genetically modified crops

BACKGROUND

Advancement in agricultural biotechnology has resulted in increasing numbers of commercial varieties of genetically modified (GM) crops worldwide. Though several databases on GM crops are available, these databases generally focus on collecting and providing information on transgenic crops rather than on screening strategies. To overcome this, we constructed a novel tool named, Genetically Modified Organisms Identification Tool (GMOIT), designed to integrate basic and genetic information on genetic modification events and detection methods.

RESULTS

At present, data for each element from 118 independent genetic modification events in soybean, maize, canola, and rice were included in the database. Particularly, GMOIT allows users to customize assay ranges and thus obtain the corresponding optimized screening strategies using common elements or specific locations as the detection targets with high flexibility. Using the 118 genetic modification events currently included in GMOIT as the range and algorithm selection results, a "6 + 4" protocol (six exogenous elements and four endogenous reference genes as the detection targets) covering 108 events for the four crops was established. Plasmids pGMOIT-1 and pGMOIT-2 were constructed as positive controls or calibrators in qualitative and quantitative transgene detection.

CONCLUSIONS

Our study provides a simple, practical tool for selecting, detecting, and screening strategies for a sustainable and efficient application of genetic modification.

Detection of Prorocentrum minimum by hyperbranched rolling circle amplification coupled with lateral flow dipstick

A novel method referred to as hyperbranched rolling circle amplification (HRCA) coupled with lateral flow dipstick (LFD) (HRCA-LFD) here was developed for specific, sensitive, rapid, and simple detection of Prorocentrum minimum. HRCA-LFD relies on a padlock probe (PLP) consisting of a common ligation sequence, two terminal sequences that complement the target DNA, and a manually designed detection probe (LFD probe). The two terminal sequences of the PLP were designed against the species-specific sites of the large subunit ribosomal DNA (LSU rDNA) D1-D2 region of P. minimum. The optimum parameters for HRCA were as follows: PLP concentration of 20 pM, ligation time of 30 min, ligation temperature of 59 °C, enzymic digestion time of 105 min, amplification time of 45 min, and amplification temperature of 58 °C. The HRCA-LFD displaying high specificity could accurately distinguish P. minimum from other microalgae. The detection limit of HRCA-LFD was as low as 1.42 × 10^-7 ng μL^-1 for genomic DNA, 1.03 × 10^-7 ng μL^-1 (approximately 27 copies) for recombinant plasmid containing the inserted LSU rDNA D1-D2, and 0.17 cells for crude DNA extract of P. minimum, which was consistently 100 times more sensitive than regular PCR. Interfering test suggested that the performance of HRCA-LFD is stable and would not be affected by other non-target species. The HRCA-LFD results of field samples that are comparable with microscopic examination confirmed that the developed method is competent for detection of target cells in field samples. In conclusion, the developed HRCA-LFD exhibiting stable performance is specific, sensitive, and rapid, which provides a good alternative to traditional microscopic examination for the detection of P. minimum cells in field samples.

Detection of genetically modified crops using multiplex asymmetric polymerase chain reaction and asymmetric hyperbranched rolling circle amplification coupled with reverse dot blot

To meet the ever-increasing demand for detection of genetically modified crops (GMCs), low-cost, high-throughput and high-accuracy detection assays are needed. The new multiplex asymmetric polymerase chain reaction and asymmetric hyper-branched rolling circle amplification coupled with reverse dot blot (RDB) systems were developed to detect GMCs. Thirteen oligonucleotide probes were designed to identify endogenous targets (Lec1, Hmg and Sad1), event-specific targets (RRS-5C, RRS-3C, Bt176-3C and MON810-3C), screening targets (35S promoter and NOS terminator), and control targets (18S and PLX). Optimised conditions were as follows: tailed hybridization probes (1-2 pmol/l) were immobilized on a membrane by baking for 2h, and a 10:1 ratio of forward to reverse primers was used. The detection limits were 0.1 μg/l of 2% RRS and 0.5 ng/l of DNA from genetically modified (GM) soybean. These results indicate that the RDB assay could be used to detect multiplex target genes of GMCs rapidly and inexpensively.

Detection of the 35S promoter in transgenic maize via various isothermal amplification techniques: a practical approach

In 2003 the European Commission introduced a 0.9% threshold for food and feed products containing genetically modified organism (GMO)-derived components. For commodities containing GMO contents higher than this threshold, labelling is mandatory. To provide a DNA-based rapid and simple detection method suitable for high-throughput screening of GMOs, several isothermal amplification approaches for the 35S promoter were tested: strand displacement amplification, nicking-enzyme amplification reaction, rolling circle amplification, loop-mediated isothermal amplification (LAMP) and helicase-dependent amplification (HDA). The assays developed were tested for specificity in order to distinguish between samples containing genetically modified (GM) maize and non-GM maize. For those assays capable of this discrimination, tests were performed to determine the lower limit of detection. A false-negative rate was determined to rule out whether GMO-positive samples were incorrectly classified as GMO-negative. A robustness test was performed to show reliable detection independent from the instrument used for amplification. The analysis of three GM maize lines showed that only LAMP and HDA were able to differentiate between the GMOs MON810, NK603, and Bt11 and non-GM maize. Furthermore, with the HDA assay it was possible to realize a detection limit as low as 0.5%. A false-negative rate of only 5% for 1% GM maize for all three maize lines shows that HDA has the potential to be used as an alternative strategy for the detection of transgenic maize. All results obtained with the LAMP and HDA assays were compared with the results obtained with a previously reported real-time PCR assay for the 35S promoter in transgenic maize. This study presents two new screening assays for detection of the 35S promoter in transgenic maize by applying the isothermal amplification approaches HDA and LAMP.

Comparison of three DNA extraction methods for feed products and four amplification methods for the 5'-junction fragment of Roundup Ready soybean

Three methods of DNA extraction from feed products and four detection methods for the 5'-junction fragment of genetically modified (GM) Roundup Ready soybean (RRS) were compared and evaluated. The DNA extraction methods, including cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and guanidine hydrochloride (Kit), were assessed for their yields and purity of DNA, extraction time, and reagent cost. The DNA yields of CTAB, SDS, and Kit were 52-694, 164-1750 and 23-105 ng/mg sample, and their extraction time was 2.5-3, 2-2.5, and 1.5-2 h with reagent cost about US dollar 0.24, 0.13, and 1.9 per extraction, respectively. The SDS method was generally well suited to all kinds of feed matrices tested. The limits of detection for the four amplification protocols, including loop-mediated isothermal amplification (LAMP), hyperbranched rolling circle amplification (HRCA), conventional polymerase chain reaction (PCR), and real-time PCR, were 48.5, 4.85, 485, and 9 copies of the pTLH10 plasmid, respectively. The ranked results of the four detection methods were based on multiattribute utility theory as follows (from best to worse): HRCA, LAMP, PCR, and real-time PCR. This comparative evaluation was specifically useful for selection of a highly efficient DNA extraction or amplification method for detecting different GM ingredients.

Construction of a reference plasmid molecule containing eight targets for the detection of genetically modified crops

A standard plasmid containing eight targets was developed for quantitative detection of genetically modified (GM) soybeans and cotton. These eight targets were joined in tandem to form the pTLE8 plasmid with a length of 3,680 bp. This plasmid contains part of the endogenous soybean Lec1 gene, the Cauliflower mosaic virus (CaMV) 35S promoter, the Agrobacterium tumefaciens nopaline synthase (NOS) terminator, the PAT gene of the soybean line A2704-12, the event-specific 5'-junction region of Roundup-Ready Soya (RRS, 35SG), the Cry1A(c) gene from Bacillus thuringiensis (Bt), the endogenous cotton Sad1 gene, and a part of RRS EPSPS gene. The PCR efficiencies with pTLE8 as a calibrator ranged from 99.4% to 100.2% for the standard curves of the RRS EPSPS gene and the taxon-specific Lec1 gene (R(2)≥0.996). The limits of detection and quantification were nine and 15 copies, respectively. The standard deviation (SD) and relative standard deviation (RSD) values of repeatability were from 0.09 to 0.52 and from 0.28% to 2.11%, and those for reproducibility were from 0.12 to 1.15 and 0.42% to 3.85%, respectively. The average conversion factor (Cf) for the CRMs RRS quantification was 0.91. The RSD of the mean values for known samples ranged from 3.09% to 18.53%, and the biases were from 0.5% to 40%. These results show that our method using the pTLE8 plasmid as a reference material (RM) is reliable and feasible in the identification of GM soybeans, thus paving the way for the establishment of identification management systems for various products containing GMO components.

Testing for genetically modified organisms (GMOs): Past, present and future perspectives

This paper presents an overview of GMO testing methodologies and how these have evolved and may evolve in the next decade. Challenges and limitations for the application of the test methods as well as to the interpretation of results produced with the methods are highlighted and discussed, bearing in mind the various interests and competences of the involved stakeholders. To better understand the suitability and limitations of detection methodologies the evolution of transformation processes for creation of GMOs is briefly reviewed.

Optimised padlock probe ligation and microarray detection of multiple (non-authorised) GMOs in a single reaction

BACKGROUND

To maintain EU GMO regulations, producers of new GM crop varieties need to supply an event-specific method for the new variety. As a result methods are nowadays available for EU-authorised genetically modified organisms (GMOs), but only to a limited extent for EU-non-authorised GMOs (NAGs). In the last decade the diversity of genetically modified (GM) ingredients in food and feed has increased significantly. As a result of this increase GMO laboratories currently need to apply many different methods to establish to potential presence of NAGs in raw materials and complex derived products.

RESULTS

In this paper we present an innovative method for detecting (approved) GMOs as well as the potential presence of NAGs in complex DNA samples containing different crop species. An optimised protocol has been developed for padlock probe ligation in combination with microarray detection (PPLMD) that can easily be scaled up. Linear padlock probes targeted against GMO-events, -elements and -species have been developed that can hybridise to their genomic target DNA and are visualised using microarray hybridisation.In a tenplex PPLMD experiment, different genomic targets in Roundup-Ready soya, MON1445 cotton and Bt176 maize were detected down to at least 1%. In single experiments, the targets were detected down to 0.1%, i.e. comparable to standard qPCR.

CONCLUSION

Compared to currently available methods this is a significant step forward towards multiplex detection in complex raw materials and derived products. It is shown that the PPLMD approach is suitable for large-scale detection of GMOs in real-life samples and provides the possibility to detect and/or identify NAGs that would otherwise remain undetected.