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José Manuel Barroso
The European Commission

13 July 2005

Dear President,

We would draw, to your personal attention, the following article by David
Schubert, a Professor in the Cellular Neurobiology Laboratory at The Salk
Institute, published as 'Regulatory Regimes for Transgenic Crops' in the journal
Nature Biotechnology (23, 785 - 787; July 2005):


Schubert is responding to Bradford et al's, 'Regulating transgenic crops
sensibly: lessons from plant breeding, biotechnology and genomics' which was
published in Nature Biotechnology in April 2005 (23(4):439-44):


You will note after analysing their arguments, Schubert concludes, "Because
of the high mutagenicity of the transformation procedures used in GE, the
assumptions made by Bradford et al. and also the FDA about the precision and
specificity of plant GE are incorrect. Nonetheless, it appears that the
positions of Bradford et al. and the biotech industry, as well as the current
regulatory framework [in the U.S.] for the labeling and safety testing of GE food
crops, is to maintain the status quo and hope for the best."

"The problem is that there are no mandatory safety testing requirements for
unintended effects and that it may take many years before any symptoms of a
GE-caused disease appear. In the absence of strong epidemiology or clinical
trials, any health problem associated with an illness caused by a GE food is
going to be very difficult, if not impossible, to detect unless it is a disease
that is unique or normally very rare."

We would be grateful for your comment.

Yours Sincerely,

Ian Panton
GMFree Cymru


By David Schubert

In a recent article Bradford and colleagues argued that the methods used to
produce food crops should not be the focus of regulatory oversight, only the
phenotypic traits of the resultant plants as defined in terms of standard
agricultural practice1. They propose that any risk and safety assessments of
crops produced by genetic engineering (GE) should be based only upon the nature
of the introduced genes. They also claim that transgenic crops face a
"daunting" array of regulatory requirements.

However, safety testing requirements in the United States are largely
voluntary and in my view inadequate. These regulations have been reviewed
elsewhere2 and will not be discussed further. Safety concerns related to the GE
process itself as well as its unintended consequences are set aside by Bradford et
al as irrelevant, for they claim that the products of genetic events that
occur naturally and with standard plant breeding techniques are fundamentally
the same as those that occur with GE. Are these arguments a valid reflection
of what is known about the precision and consequences of the GE process as
compared with naturally occurring genomic variation?

The basic assumption underlying the concept of a one-to-one relationship
between the transgene and the resultant phenotype is that the GE process is
relatively precise. However, none of the current transgene insertion techniques
permit control over the location of the insertion site or the number and
orientation of the genes inserted. Indeed, over one-third of all
Agrobacterium-mediated insertion events disrupt functional DNA3,4. These and related
transformation and cell culture-induced changes in chromosomal structure have been
recently documented in great detail5. For example, translocations of up to
40 Kb6, scrambling of transgene and genomic DNA7, large scale deletions of
over a dozen genes8 and frequent random insertions of plasmid DNA9 can all be
caused by the procedures used to make GE plants. In fact, the most commonly
used transformation procedure is sometimes itself used as a mutagen10, and can
activate dormant retrotransposons that are highly mutagenic11. Moreover,
mutations linked to the transgene insertion site cannot be removed by additional
breeding as long as there is selection for the transgene itself. Collectively
these data indicate that the GE process itself is highly mutagenic.

Some modern breeding technologies introduce new traits into plants via
chemical or radiation mutagenesis or by wide cross hybridizations that overcome
natural species barriers. Mutagenesis was used in the United States during the
middle part of the last century, but food crops made by this technique now
constitute less than a few percent of US production, with sunflowers being the
major representative12. However, plants produced by wide crosses, such as
those between quackgrass and bread wheat to yield a widely planted grain that
has all of the chromosomes of wheat and an extra half genome of the
quackgrass, while unique, are fundamentally different from those produced by either
mutagenesis or GE. In wide crosses and other forms of ploidy manipulation
there are clearly changes in gene dosage, and proteins unique to only one parent
can be produced in the hybrid, but there is no a priori reason to assume
that mutations are going to occur simply because there is a change in chromosome
or gene number. While the extent and suddenness of all of these modern
breeding technologies are unlike anything known to occur during the course of
evolution or with traditional breeding, only GE and mutagenesis introduce large
numbers of mutations. Any new cultivars derived by the latter two methods
should be subjected to similar regulatory requirements.

Bradford et al. correctly state that plants normally contain the same
Agrobacterium and viral DNA sequences that are used to create GE transfection
constructs, but fail to point out that with GE these pieces of DNA are part of a
cassette of genes for drug resistance along with strong constitutive viral
promoters that are used to express foreign proteins at high levels in all parts
of the plant, hardly a natural event. They incorrectly imply that changes in
ploidy, gene copy number, recombination, and high genomic densities of
transposable elements in normal plants continually lead to mutations and changes
in gene expression similar to those caused by GE.

Ploidy is notoriously unstable in plants, but changes involve moving around
large blocks of intact genes while maintaining their regulated expression
pattern. It should also be remembered that recombination is not the same as
random mutagenesis, for there has been tremendous selective pressure for alleles
to express functionally similar proteins. The statement that
"retrotransposons continuously insert themselves between genes" is incorrect, for these
high copy number elements are transpositionally inactive in normal modern food
plants13, have evolved and rearranged in the distant past14, but can be acti
vated by tissue culture or by mutagenesis11. In fact their discovery by
Barbara McClintock was facilitated by the use of mutagenized corn13.

While Bradford et al. propose that regulatory efforts should be focused upon
the expression of the transgene, I believe that the major hazards of the
highly mutagenic plant transformation techniques are the potentials for a
decrease in nutritional content or an increase in dangerous metabolites. While it
is widely recognized that the breeding of some crops can produce varieties
with harmful characteristics, millennia of experience have identified these
crops, and breeders test new cultivars for known harmful compounds, such as
alkaloids in potatoes15,16. In contrast, unintended consequences arising from
the random and extensive mutagenesis caused by GE techniques opens far wider
possibilities of producing novel, toxic, or mutagenic compounds in all sorts of
crops. Unlike animals, plants accumulate thousands of nonessential small
molecules that provide adaptive benefits under conditions of environmental or
predator-based stress17. Estimates are that they can make between 90,000 and
200,000 phytochemicals with up to 5000 in one species18. These compounds are
frequently made by enzymes with low substrate specificity19 in which
mutations can readily alter substrate preference20,21

There are many examples of unpredictable alterations in small molecule
metabolism in GE organisms. In yeast genetically engineered to increase glucose
metabolism, the GE event caused the unintended accumulation of a highly toxic
and mutagenic 2-oxoaldehyde called methylglyoxal22. In a study of just 88
metabolites in four lines of potatoes transformed for altered sucrose
metabolism, Roessner et al. found that the amounts of the majority of these
metabolites were significantly altered relative to controls18. In addition, nine of
the metabolites in GE potatoes were not detected in conventional potatoes.
Given the enormous pool of plant metabolites, the observation that 10% of those
assayed are new in one set of transfections strongly suggests that
undesirable or harmful metabolites may be produced and accumulate23. Contrary to the
suggestions of Bradford et al., Kuiper and his colleagues strongly recommend
that each transformation event should be assayed for these types of unintended
events by metabolic profiling24.

A well documented horticultural example of unintended effects is the
alteration in the shikimic acid pathway in Bt corn hybrids derived from Monsanto's
MON810 and Syngenta's Bt11 plants as well as glyphosate-tolerant soybeans.
Stem tissue of both groups of plants has elevated levels of lignin, an abundant
non-digestible woody component that makes the plants less nutritious for
animal feed25,26. Components of this same biochemical pathway also produce both
flavonoids and isoflavonoids that have a high nutritional value, and
rotenone, a plant-produced insecticide that may cause Parkinson's disease27.
Isoflavonoids are abundant in legumes like soy beans, and rotenone is synthesized
directly from isoflavones in many legume species28. Because of the
promiscuity of many plant enzymes and the large and varied substrate pools of
phytochemical intermediates, it is impossible to predict the products of enzymes or
regulatory genes mutated during the GE event23. While I are not aware of any
testing of GE soybeans for rotenone, it has been shown that
glyphosate-tolerant soybeans sprayed with glyphosate have a reduced flavonoid content29.

The safety testing of GE crops need not be as extensive as that done with
drugs, food additives or cosmetics. Many suggestions have been put forward
(see, for example 30,2,5,24) including those by the World Health Organization31.
I believe that the most important safety tests include metabolic profiling
to detect unexpected changes in small molecule metabolism24 and the Ames test
to detect mutagens32. Molecular analysis of the gene insertion sites and
transformation-induced mutations5 should also be performed along with both
multigenerational feeding trials in rodents to assay for teratogenic effects and
developmental problems, and allergenicity testing performed according to a
single rigorous protocol31 The animal studies are of particular importance for
crops engineered to produce precursors to highly biologically active
compounds such as Vitamin A and retinoic acid, molecules that can act as teratogens
at high doses33.

In summary, Bradford et al. state that there is a low risk from the
consumption of GE plants "where no novel biochemical or enzymatic functions are
imparted". The question is, of course, how can one know if a novel and
potentially harmful molecule has been created unless the testing has been done? How can
one predict the risk in the absence of an assay? Because of the high
mutagenicity of the transformation procedures used in GE, the assumptions made by
Bradford et al. and also the FDA 34 about the precision and specificity of
plant GE are incorrect. Nonetheless, it appears that the positions of Bradford
et al. and the biotech industry, as well as the current regulatory framework
for the labeling and safety testing of GE food crops, is to maintain the
status quo and hope for the best.

The problem is that there are no mandatory safety testing requirements for
unintended effects2 and that it may take many years before any symptoms of a
GE-caused disease appear. In the absence of strong epidemiology or clinical
trials, any health problem associated with an illness caused by a GE food is
going to be very difficult, if not impossible, to detect unless it is a disease
that is unique or normally very rare. Therefore, while GE may be able to
enhance world health and food crop production , its full potential is likely to
remain unfulfilled until rigorous pre-release safety testing can provide
some assurance to consumers that the products of this new technology are safe to

1. Bradford, K. J., Van Deynze, A., Gutterson, N., Parrott, W. & Strauss,
S. H. Regulating transgenic crops sensibly: lessons from plant breeding,
biotechnology and genomics. Nat Biotechnol 23, 439-44 (2005).
2. Freese, W. & Schubert, D. Safety testing of genetically engineered
food. 21 Biotechnology and Genetic Engineering Reviews, 299-325 (2004).
3. Szabados, L. et al. Distribution of 1000 sequenced T-DNA tags in the
Arabidopsis genome. Plant J 32, 233-42 (2002).
4. Forsbach, A., Schubert, D., Lechtenberg, B., Gils, M. & Schmidt, R. A
comprehensive characterization of single-copy T-DNA insertions in the
Arabidopsis thaliana genome. Plant Mol Biol 52, 161-76 (2003).
5. Wilson, A., Latham, J. & Steinbrecher, R. 35 (EcoNexus, Brighton, UK,
6. Tax, F. E. & Vernon, D. M. T-DNA-associated duplication/translocations
in Arabidopsis. Implications for mutant analysis and functional genomics.
Plant Physiol 126, 1527-38 (2001).
7. Makarevitch, I., Svitashev, S. K. & Somers, D. A. Complete sequence
analysis of transgene loci from plants transformed via microprojectile
bombardment. Plant Mol Biol 52, 421-32 (2003).
8. Kaya, H. et al. Hosoba toge toge, a syndrome caused by a large
chromosomal deletion associated with a T-DNA insertion in Arabidopsis. Plant Cell
Physiol 41, 1055-66 (2000).
9. Kim, S. R. et al. Transgene structures in T-DNA-inserted rice plants.
Plant Mol Biol 52, 761-73 (2003).
10. Weigel, D. et al. Activation tagging in Arabidopsis. Plant Physiol
122, 1003-13 (2000).
11. Hirochika, H., Sugimoto, K., Otsuki, Y., Tsugawa, H. & Kanda, M.
Retrotransposons of rice involved in mutations induced by tissue culture. Proc
Natl Acad Sci U S A 93, 7783-8 (1996).
12. Ahloowalia, B. S., Maluszynski, M. & Nichterlein, K. Global impact of
mutation-derived varieties. Euphytica 135, 187-204 (2004).
13. Feschotte, C., Jiang, N. & Wessler, S. R. Plant transposable
elements: where genetics meets genomics. Nat Rev Genet 3, 329-41 (2002).
14. Brunner, S., Fengler, K., Morgante, M., Tingey, S. & Rafalski, A.
Evolution of DNA Sequence Nonhomologies among Maize Inbreds. Plant Cell 17,
343-60 (2005).
15. Korpan, Y. I. et al. Potato glycoalkaloids: true safety or false
sense of security? Trends Biotechnol 22, 147-51 (2004).
16. Ewen, S. W. & Pusztai, A. Effect of diets containing genetically
modified potatoes expressing Galanthus nivalis lectin on rat small intestine.
Lancet 354, 1353-4 (1999).
17. Verpoorte, R. in Metabolic Engineering of Plant Secondary Metabolism
(eds. Verpoorte, R. & Alfermann, A. W.) 1-29 (Kluwer Academic Publishers,
Dordrecht , The Netherlands, 2000).
18. Roessner, U. et al. Metabolic profiling allows comprehensive
phenotyping of genetically or environmentally modified plant systems. Plant Cell 13,
11-29 (2001).
19. Schwab, W. Metabolome diversity: too few genes, too many metabolites?
Phytochemistry 62, 837-49 (2003).
20. Zubieta, C. et al. Structural basis for substrate recognition in the
salicylic acid carboxyl methyltransferase family. Plant Cell 15, 1704-16
21. Johnson, E. T. et al. Alteration of a single amino acid changes the
substrate specificity of dihydroflavonol 4-reductase. Plant J 25, 325-33
22. Inose, T. & Murata, K. Enhanced accumulation of toxic compound in
yeast cells having high glycolytic activity: A case study on the safety of
genetically engineered yeast. Intl J Food Sci Tech 30, 141-6 (1995).
23. Grotewold, E. Plant metabolic diversity: a regulatory perspective.
Trends Plant Sci 10, 57-62 (2005).
24. Kuiper, H. A., Kleter, G. A., Noteborn, H. P. & Kok, E. J. Assessment
of the food safety issues related to genetically modified foods. Plant J 27,
503-28 (2001).
25. Saxena, D. & Stotzky, G. Bt corn has a higher lignin content than
non-Bt corn. Amer J Botany 88, 1704-6 (2001).
26. Gertz, J. M., Vencill, W. K. & Hill, N. S. in Proceedings of the 1999
Brighton Crop Protection Conference: Weeds 835-840 (British Crop Protection
Council, Farnham, UK, 1999).
27. Betarbet, R. et al. Chronic systemic pesticide exposure reproduces
features of Parkinson's disease. Nature Neurosci. 3, 1301-1306 (2000).
28. Morgan, E. D. & Wilson, I. D. in Comprehensive Natural Products
Chemistry (ed. Mori, K.) 363-375 (Pergamon Press/Elsevier Science, Oxford, 1999).
29. Lappe, M. A., Bailey, E. B., Childress, C. & Setchell, K. D. R.
Alterations in clinically important phytoestrogens in genetically modified,
herbicide-tolerant soybeans. J Med Foods 1, 241-245 (1999).
30. Edmonds_Institute. Manual for assessing ecological and human health
effects of genetically engineered organisms. (Edmonds Institute, 1998).
31. FAO-WHO. Evaluation of Allergenicity of genetically modified foods.
Report of a Joint FAO/WHO expert consultation on allergenicity of foods
derived from biotechnology. January 22-25, 2001. (2001).
32. Maron, D. M. & Ames, B. N. Revised methods for the Salmonella
mutagenicity test. Mutat Res 113, 173-215 (1983).
33. McCaffery, P. J., Adams, J., Maden, M. & Rosa-Molinar, E. Too much of
a good thing: retinoic acid as an endogenous regulator of neural
differentiation and exogenous teratogen. Eur J Neurosci 18, 457-72 (2003).
34. Kessler, D. A., Taylor, M. R., Maryanski, J. H., Flamm, E. L. & Kahl,
L. S. The safety of foods developed by biotechnology. Science 256, 1747-9,
1832 (1992).