Gene deletor: a new tool to address gene flow and food safety concerns over transgenic crop plants

Confirmation of 'Pollen- and Seed-Specific Gene Deletor' System Efficiency for Transgene Excision from Transgenic Nicotiana tabacum under Field Conditions

The commercial application of genetically modified plants has been seriously impeded by public concern surrounding the potential risks posed by such plants to the ecosystem and human health. Previously, we have developed a 'pollen- and seed-specific Gene Deletor' system that automatically excised all transgenes from the pollen and seeds of greenhouse-grown transgenic Nicotiana tabacum. In this study, we conducted seven field experiments over three consecutive years to evaluate the stability of transgene excision under field conditions. Our results showed that transgenes were stably excised from transgenic Nicotiana tabacum under field conditions with 100% efficiency. The stability of transgene excision was confirmed based on PCR, as well as the GUS staining patterns of various organs (roots, leaves, petiole, stem, flower, fruit, and seeds) from transgenic N. tabacum. In six transgenic lines (D4, D10, D31, D56, and D43), the transgenes were stably deleted in the T0 and T1 generations. Thus, the 'Gene Deletor' system is an efficient and reliable method to reduce pollen- and seed-mediated unintentional gene flow. This system might help to alleviate the food safety concerns associated with transgenic crops.

TECHNOLOGIES OF GENETIC MATERIAL USE RESTRICTION: TYPES, MOLECULAR-GENETIC BASE AND ETHICAL ANALYSIS OF THEIR APPLICATION

In order to save money, some farms use the seed obtained in the process of cultivation not only for sale, but also for sowing, which has not found supporters among companies engaged in the production of genetically modified seed. To protect their rights, the latter have created technologies to limit the use of genetic material, which are intended to be used for protection the intellectual rights to reproduce plants with a changed genotype. However, these technologies contain also a commercial component and violate a number of moral principles and international acts. Aim. To describe the types of terminator technologies, their genetic and molecular basis and purpose. To assess a correspondence of their compliance with the international documents and norms. Method. Terminator technologies types, genetic bases and application and their analysis from the standpoint of international norms were studied. To achieve the goal, the methods of fact analysis, comparison and generalization were used. Results. There are two types of terminator technologies (variety- and trait-specific), which are based on the interaction of three genes, which leads to the implementation of certain phenotypic manifestations. It was found that the technologies for limiting the use of genetic material are both contradictory and consistent with a number of international legal acts, which did not make it possible to determine clearly the appropriateness of their use in agriculture. Conclusions. Terminator technologies application is still a controversial fact since they are based on the duality principle: to carry simultaneously a positive and a negative manifestation for people.

Heat-Shock-Induced Removal of Transgenes Using the Gene-Deletor System in Hybrid Aspen (Populus tremula × P. tremuloides)

To evaluate the efficacy of the gene-deletor system in aspen, we evaluated the system for foreign gene removal in a hybrid aspen clone, INRA 353-53 (Populus tremula × P. tremuloides). The recombinase flipping DNA (FLP) gene was under the control of the heat-inducible promoter of Gmhsp17.6-L, and the β-glucuronidase (gusA) gene which was under the control of the 35S promoter and were constructed using the gene-deletor system in the pCaLFGmFNLFG vector. Six transgenic plants and their sublines were heated at 42 °C for 8 h and gene deletion was verified by polymerase chain reaction (PCR). Three lines exhibited partial transgene deletion while the remaining three lines did not delete. Transgenic lines were evaluated by Southern-blot analyses, verifying that the six transgenic plant lines all had a single copy of transfer DNA (t-DNA). Two partial-deletion lines and two non-deletion lines were analysed for methylation and expression of promoter and recombinase. Hardly any methylation was detected in the Gmhsp17.6-L promoter or recombinase FLP gene sequences, however, the expression of the promoter and recombinase was increased significantly in the partial-deletion compared with the non-deletion line after heat-shock treatment. These results suggest that the excision efficiency had no direct relationship with methylation status of the Gmhsp17.6-L promoter and FLP recombinase, yet was affected by the expression of the Gmhsp17.6-L and FLP after heat-shock treatment.

Structure of Exogenous Gene Integration and Event-Specific Detection in the Glyphosate-Tolerant Transgenic Cotton Line BG2-7

In this study, the flanking sequence of an inserted fragment conferring glyphosate tolerance on transgenic cotton line BG2-7 was analyzed by thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR) and standard PCR. The results showed apparent insertion of the exogenous gene into chromosome D10 of the Gossypium hirsutum L. genome, as the left and right borders of the inserted fragment are nucleotides 61,962,952 and 61,962,921 of chromosome D10, respectively. In addition, a 31-bp cotton microsatellite sequence was noted between the genome sequence and the 5' end of the exogenous gene. In total, 84 and 298 bp were deleted from the left and right borders of the exogenous gene, respectively, with 30 bp deleted from the cotton chromosome at the insertion site. According to the flanking sequence obtained, several pairs of event-specific detection primers were designed to amplify sequence between the 5' end of the exogenous gene and the cotton genome junction region as well as between the 3' end and the cotton genome junction region. Based on screening tests, the 5'-end primers GTCATAACGTGACTCCCTTAATTCTCC/CCTATTACACGGCTATGC and 3'-end primers TCCTTTCGCTTTCTTCCCTT/ACACTTACATGGCGTCTTCT were used to detect the respective BG2-7 event-specific primers. The limit of detection of the former primers reached 44 copies, and that of the latter primers reached 88 copies. The results of this study provide useful data for assessment of BG2-7 safety and for accelerating its industrialization.

Engineered selective plant male sterility through pollen-specific expression of the EcoRI restriction endonuclease

Unintended gene flow from transgenic plants via pollen, seed and vegetative propagation is a regulatory concern because of potential admixture in food and crop systems, as well as hybridization and introgression to wild and weedy relatives. Bioconfinement of transgenic pollen would help address some of these concerns and enable transgenic plant production for several crops where gene flow is an issue. Here, we demonstrate the expression of the restriction endonuclease EcoRI under the control of the tomato pollen-specific LAT52 promoter is an effective method for generating selective male sterility in Nicotiana tabacum (tobacco). Of nine transgenic events recovered, four events had very high bioconfinement with tightly controlled EcoRI expression in pollen and negligible-to-no expression other plant tissues. Transgenic plants had normal morphology wherein vegetative growth and reproductivity were similar to nontransgenic controls. In glasshouse experiments, transgenic lines were hand-crossed to both male-sterile and emasculated nontransgenic tobacco varieties. Progeny analysis of 16 000-40 000 seeds per transgenic line demonstrated five lines approached (>99.7%) or attained 100% bioconfinement for one or more generations. Bioconfinement was again demonstrated at or near 100% under field conditions where four transgenic lines were grown in close proximity to male-sterile tobacco, and 900-2100 seeds per male-sterile line were analysed for transgenes. Based upon these results, we conclude EcoRI-driven selective male sterility holds practical potential as a safe and reliable transgene bioconfinement strategy. Given the mechanism of male sterility, this method could be applicable to any plant species.

Genetic use restriction technologies: a review

Genetic use restriction technologies (GURTs), developed to secure return on investments through protection of plant varieties, are among the most controversial and opposed genetic engineering biotechnologies as they are perceived as a tool to force farmers to depend on multinational corporations' seed monopolies. In this work, the currently proposed strategies are described and compared with some of the principal techniques implemented for preventing transgene flow and/or seed saving, with a simultaneous analysis of the future perspectives of GURTs taking into account potential benefits, possible impacts on farmers and local plant genetic resources (PGR), hypothetical negative environmental issues and ethical concerns related to intellectual property that have led to the ban of this technology.