The creation of transgenic plants often involves the use of DNA sequences from bacteria and other non-plant organisms – in particular as vectors to introduce the desired genes. However, some people are concerned about the use of DNA from such distantly related sources, and regulators require separate rules to be complied with for transgenic plants compared to those derived by selective breeding. Could using plant-derived sequences help address those fears and reduce the regulatory burden for crop biotechnologists?
Tony Conner and his colleagues from Plant and Food Research, New Zealand consider the potential for intragenic vectors in a paper in CAB Reviews. This involves finding DNA fragments within a plant species that are very similar to those from foreign DNA that have been used as vectors for many years. Various techniques have been developed, some involving small amounts of foreign DNA, but fully intragenic plants have no foreign DNA and are entirely composed from plant-derived sequences.
Conner and his co-workers pose the question: "Does it really matter where a DNA sequence comes from if the sequence is essentially identical? While the source of DNA may appear irrelevant in the scientific context of a physical sequence, many people infer more from DNA than a physical sequence. It is also associated with the "spirit" or "essence of being". For intragenic plants to be advocated as a more ethical approach to genetic modification it is important that they are clean of all foreign DNA".
They point out that the technique produces plants with a minor rearrangement of their own DNA sequences. They argue that this is equivalent to the rearrangements that occur spontaneously in nature and via radiation treatment, both used for many years as sources of variation in breeding to produce new plant species with much less regulation than is required for transgenic plants. Some argue that plants produced by the new technique should be exempt from the more stringent regulation, but others believe that a random insertion of DNA, even though of plant origin, still poses the risk of unpredictable outcomes. However, Conner and his colleagues believe that the latter view overlooks the role that natural rearrangements play.
Conner and his colleagues think that the main reason for using intragenic vectors is not to control risk, but to address the ethical issues associated with the transfer of DNA across taxonomic boundaries. Given that such vectors are comparable to natural rearrangements, and that the risk profile of intragenic vectors and transgenic vectors is no different, the intragenic approach could "help to establish that there is nothing inherently unsafe about GM plants." The technology means that there is no longer a clear biological distinction between traditional plant breeding and development of GM crops, but a continuum of technologies. "There is no longer a clear point of demarcation on which to base a legal definition of genetic modification which has biological relevance and is enforceable by law," say the authors..
Conner and his co-authors recognise that for some, ethical opinions on GM plants are deeply held with no room for compromise. However, they think the intragenic approach has promise: "We believe that this approach will provide a socially acceptable and responsible way forward for the development of GM crops."
The paper,Intragenic vectors for plant transformation within gene pools, by P.J. Barrell, J.M.E. Jacobs, S.J. Baldwin, A.J. Conner, appears in CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2010, 5, No. 010, 18 pp. It is also available via AgBiotechNet.