Mae Wan Ho1 states that genetic engineering is fundamentally different from conventional plant breeding or wide crosses to produce novel crops; thus she concludes that genetically modified (GM) plants need unique tests on their safety.
Any new crop should have its composition of major and minor constituents investigated to establish substantial equivalence, and its novel trait independently tested, as has been the case for the present range of GM plants. However, Ho states that special tests are required because “genetic engineering enables exotic genes… [to be] combined in novel constructs, often with viral promoters to make genes overexpress continuously. The constructs are inserted into genomes by transformation techniques that cannot control where the genes go, resulting in a range of unpredictable positional effects and rearrangements”2.
But this differs little, if at all, from Ho's description of normal genome behaviour in her book2, which states: “Genome organisation is infinitely variable [and contains] transposons that can excise and reinsert elements in different locations in the genome” and “up to 20% of some genomes may contain reverse transcripts. These processes destabilise genes and genomes, move genes around, mutate, rearrange, recombine, replicate sequences …”. What could be more exotic than a mutant protein?
Some estimates suggest that the genome of some cereals may contain up to 50% retrotransposons; transposons contain end regions that are hot spots for recombination using transposase. The plant genome contains very large numbers of strong promoters that direct expression as strongly as any viral promoter such as the cauliflower mosaic virus 35S promoter. These pro-moters are used experimentally; many of them are constitutively and continuously expressed because they control the expression of housekeeping genes. We know the consequences of events via random GM insertion from libraries constructed from T-DNA insertion. However, Ho and other critics of GM technology neglect the extent to which selection is made among many GM transformants, as is the case with conventional plant breeding among siblings. Lethal insertions are self-selecting; potentially innocuous insertions are detected by substantial equivalence.
It is important to recognize that all the food we eat has been (and is) continuously genetically engineered by natural phenomena in ways that do not differ in any fundamental way from the current GM technology. Natural genetic modification of wheat3 and rice, for example, enabled the breeding of dwarf crops, used to feed many millions in the ‘Green Revolution’.
To criticize experimental GM technology while accepting the benefits of natural GM implicit in ‘the fluid genome’2 hints at a not uncommon attitude that sees synthetic pesticides as morally reprehensible but natural pesticides as good. Is this really any different from notions of Original Sin?
Ho, M.-W. Nature 402, 575 (1999).
Ho, M.-W. Genetic Engineering: Dream or Nightmare? (Gateway, Bath, 1998).
Peng, J. et al. Nature 400, 256–261 (1999).
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Trewavas, A., Leaver, C. How nature itself uses genetic modification. Nature 403, 12 (2000). https://doi.org/10.1038/47345