Workshop on "Genetic Interactions"
A workshop on Genetic Interactions was organised within the framework of the ESF AIGM Programme, in Lisbon on 19-23 September 2001.
This workshop dealt with the impact of genetic interactions in GM safety assessment in comparison to the conventional genetic interactions in plant breeding and transgene expression instability; gene silencing of transgenes, virus induced silencing and plant host gene interactions, and how we avoid transgene instability.
Conclusions of the workshop
The session on Friday morning (21/9) illustrated various aspects of viral infections and the impact on gene expression and genome stability. It was shown that a virus could modulate the expression of transgenes that contain sequences from the virus, for example, a promoter or a segment with poly-adenylation signal sequences. A frequently used promoter in transgenic plants is the 35S promoter of the Cauliflower Mosaic Virus and it was clearly demonstrated that the activity of this promoter is reduced when the plant gets infected with the virus. The full-scale implication of these effects is not well established. The examples indicate however that one should be aware of possible changes in the trait introduced by the transgene as a result of a virus infection.
Several viruses encode proteins that block PTGS of endogenous plant genes, which is induced by homologous transgenes. Therefore, a trait based on silencing of an endogenous gene could get lost when a virus infects the plants. In a number of transgenic crops the introduced trait is based on PTGS but whether viral infections under field conditions impose a real threat is unclear. If the transgene-induced trait is delayed-fruit-ripening, or the synthesis of a particular type of starch, or a change in flower pigmentation, loosing the trait by a viral infection is mostly a risk for the grower. Inevitably this costs money but there is no direct danger for the consumer. The situation becomes different when the trait is, for example, the inhibition of the synthesis of a plant toxin. When in this case the trait is lost due to a viral infection there is a potential danger for the consumer if one doesn’t check the product for the presence of toxins. One can therefore consider being selective and imposing guidelines for the application of transgene-induced PTGS in genetically modified crops until more is known about the real impact of virus infections on PTGS under field conditions.
An argument against GMPs often brought forward is that one does not know where the transgene integrates into the genome and that ’anything can happen’ and that it is uncontrolled. That one cannot predict where the transgene becomes inserted is true but there are several ways to examine afterwards where the transgene is and whether it affects the expression of neighboring plant genes. But one should keep in mind that under normal conditions, pieces of DNA frequently rearranges due to the activity of transposable DNA elements and integrations of viruses. These events cannot be controlled as they happen spontaneously. This was illustrated on the hand of viral integrations in banana, tobacco, and petunia. It is extremely hard to find out the effect of these events on gene expression and performance of the plant as a whole but breeding experience has learned that this is not a big problem because continuous selection is common practice. In the case of GMPs this will not be different and moreover, the genetic change of the introduced transgene is relatively small and is fully characterized in contrast to the genetic changes that are normally occurring in the genome. Not to speak of the genetic changes involved in crossings with wild species where there is a massive introduction of ’unknown’ genetic material. But here again this is common breeding practice with the introduction of disease resistance in existing crops, for example.
Everyone agreed that safety assessment is an important issue to gain public support for the introduction of GMPs and biotechnology in general. Adrian Butt presented an overview of the various steps in safety assessment. It was emphasized that risk assessment should be evidence-based and hypothesis-driven. It was noticed that GMPs are treated differently than crops obtained by regular breeding. GMPs must be examined in much greater detail than non-GMPs and several experts believe this is not always needed. Indeed from a technical viewpoint it might not be needed but if it helps to improve the public acceptance of GMP technology it should be done despite the mixed feelings that are around.
The participants agreed that the communication between scientists working with genetically modified plants and the public community needs improvement. This needs the involvement of "communication professionals".
Plant gene silencing research in Europe is highly advanced and competitive with research in the US and Japan due to the well-established EU network of European laboratories working in the field. Gene silencing research has revealed general rules for stable expression of transgenes in plants and the avoidance of gene suppression, i.e. avoidance of multi-copy inserts or inverted repeat structures and use of promoters with moderate expression level.
The production of interspecific somatic hybrids is accompanied by extensive somaclonal variation and therefore needs tight screening and selection approaches.
The participants agreed that the transformation of chloroplast has so far not reached a broad applicability.
The participants discussed the need to minimize the remain of vector and marker gene sequences in genetically modified plants going into the market. Commercial aspects were discussed and it was concluded that European legislative and executive regulations are still behind the scientific development.
It was pointed out that the effect of scale in genetic interaction of newly introduced genes with the plant genome can only be properly evaluated by carrying out field trials with genetically modified plants.
The two main take-home messages were that: we need a carefully balanced analysis for risk assessment programmes that take into account the justified request by the public (especially of the developed world) for a safe use of GM technology, and the equally justified request (especially by the developing world) to exploit GM technologies to combat food shortages and to reduce agricultural practices that cause environmental damage.
The impressive improvement in our understanding of post-transcriptional gene silencing via ds RNA has provided us with very powerful tools for the elimination of unfavourable gene, which will broaden the spectrum of novel crop plants in the future. At the same time, this has even enhanced the focus on the need to control reliable expression of transgenes, which will be a major challenge for future research.
There appears to be little realistic alternative to Antibiotic Resistant Markers (ARMs). Proposed alternative systems are NOT likely to have more acceptance scientifically and in regulatory circles than current ARMs. This leave a requirement to revisit the acceptance, public and government of some of less medically applicable ARMs in current use.
The mechanism of gene and transgene expression is not so exacting as textbook definitions, these flexibilities in expression and interaction must be considered more carefully, and discussed more openly, as portraying such interactions so precisely may lead to additional problems.
GMO regulation must remain science based, and genetic interactions are only relevant if they have a bearing on safety (food, feed and environmental) or detection (labeling) an endless requests for genetic data is not productive.
Best practice
Industry and Government and interested stakeholders should look to develop a “Best Practice” in relation to development of GM products to minimise uncertainty and un-necessary research. This should focus on products that avoid complex genetic and environmental questions and should dictate constructs that limit potential for unintended effects.
One of the key points of the Best Practice philosophy is that it provides an approach to avoiding both identifiable as well as non-identifiable hazards. The three principles of best practice are:
- Avoid or minimise the inclusion of superfluous transgenes or sequences;
- Avoid or minimise superfluous expression of the transgene;
- Avoid or minimise the disperal of transgenes into the environment.
Recommendations
To access the long term ecological impacts of GMC the following recommendations for risk assessment are made:
- Focus on the wider ecological environment (and conservation issues);
- Focus on the immediate agroecological situation in which the crop is located;
- Take account of the geographical dimensions of target and non-target species;
- Include appropriate hypotheses for potential hazards, which can then be empirically tested;
- Take account of the different scales within which such processes act, and ensure that all extrapolations, i.e. from small-scale to large-scale and short-term to long-term, are valid, well-tried and tested.
- Evaluate risks in terms of current practices – or at least the most “harmless” options rather than against zero risk scenarios.
Biosafety Research and Monitoring
Combined efforts made by scientists, industrial companies, and regulating authorities are necessary to realise the next generation of transgenic plants which are suitable for the EU market. One step towards this objective was the „Biosafety Research and Monitoring“ announcement by the German Ministry for Education and Research (BMBF). In April 2001 they started funding scientific investigations which, among others, deal with the following problems:
- Establishment of new strategies to limit transferred gene sequences to what is necessary to assure functionability;
- Development of alternatives to the marker genes available for the selection of genetically modified plants;
- Design of new strategies for the elimination of gene sequences which became void after successful selection;
- Development of optimised binary vectors to generate transgenic plants free from unwanted sequences;
- Development of methods for sequence-specific integration of transgenes into the plant genome and for in situ modification of plant genes;
- Limitation of spreadability of transgenes.
The German BMBF-funded cluster project „Targetted transfer of minimised transgene sequences with optimised function“ aims to develop new strategies covering the necessary range of different approaches and/or to test them for their applicability. The wide range of approaches is required since one cannot expect that a general solution for minimising transgene sequences while maintaining optimum function will be found.
Co-ordinator
- Maria SaloméPaisE-Mail
- Universidade de LisboaFaculdade de CienciasDept. Biologia VegetalLisboaPortugal
