Environmental risk assessment

Despite the scientific advantages made in crop improvement, the commercialization of genetically engineered plants has been slowed by public concerns on the issue of the environmental safety of genetically engineered organisms. The assumption underlying regulations is that all transgenic plants are potentially hazardous because of the gene transfer method(s) used. However, as public experience and understanding of plant transformation increase, it is hoped that regulatory process to assess environmental risk will focus on products of the transgene expression rather than on the method of gene transfer.

Regulatory agencies and commercial interests are concerned about the environmental impact, distribution uncertainty, and public perception of widespread release of organisms expressing genes that confer resistance to antibiotics or herbicides. Although products of expression of such genes are not necessarily harmful [72] these concerns can be alleviated by removing selection markers from the host genome. Selectable markers can be eliminated by a Cre/Lox site-specific recombination. [73] However, to suggest that it should be used to remove marker genes is to fail to appreciate the implications of applying the method to agronomically important crops. For vegetatively propagated crops, the Cre/Lox system would be particularly cumbersome since the necessary sexual crosses and seed production scramble the elite genome. Therefore, if regulatory agencies decided that selectable markers should be removed, crops such as potato, apple and strawberry would be much more difficult to improve using plant biotechnology.

Selectable marker genes not only are essential to those constructing genetically modified plants but also are useful to plant breeders, legislative bodies, and monitoring agencies. Plant breeders can use selectable markers to identify progeny of crosses which contain the gene of agronomic interest because the two are linked. This saves the breeder having to assay the gene of commercial interest by more complex and expensive methods such as Southern and PCR analyses based on the utilization of specific probes and primers. Very importantly, selectable markers can be used by breeders, and by regulatory and monitoring agencies to distinguish transgenic from non-transgenic plants by a simple test which does not involve advanced molecular biology.