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ISIS Report 06/12/06
Universal Condemnation Meets UK Government’s Green Light for
GM Potato Trials
Assumptions
of safety not justified by existing evidence
The government must withdraw permission for the trials, or the regulators
should be held responsible for any harm caused. Dr.
Mae-Wan Ho and Prof. Joe Cummins
A fully referenced
version of this paper is posted on ISIS members’ website. Details
here.
Big food companies reject GM potatoes and oppose the trials
The UK government has given permission to German biotech company BASF Plant Science
GmbH for the first trials of a genetically modified (GM) crop in the country
since 2003 [1]. BASF’s GM blight-resistant potato was granted permit for field
trials in Ireland earlier this year, but the company abandoned
its plans in face of strong opposition from civil society organisations and
strict conditions imposed by Ireland’s Environmental Protection Agency [2].
The big food
companies in the United States, including McDonalds, McCains, Burger King
and Pringles, had rejected GM potatoes in 2002; and in August 2006, when BASF
applied for a UK trial permit, the British Retail Consortium said UK supermarkets
would not be stocking GM potato [3].
The British Potato Council has also made its strong opposition
known the day after the government’s decision was announced [4]. It refused
to endorse the trials, and said it was paramount that public concerns were
addressed, and fears about possible cross-contamination allayed, before trials
began. The trials are to consist of five-acre plots in Derbyshire and Cambridgeshire
for five years beginning 2007, under the conditions that the plots must be
left fallow after the five-year trial so any remaining tubers can be destroyed
and none of the potatoes harvested enters the food chain.
The GM potatoes
are modified with genes from a wild Mexican relative of potato, Solanum bulbocastanum,
intended to make them resistant to the fungus causing late blight disease;
but they also have marker traits, including herbicide resistance. BASF has
not done environmental or health impact studies on the GM potatoes
[5]. In view of
the growing list of damning evidence against the safety of GM crops [6, 7]
(GM Soya Fed
Rats: Stunted, Dead, or Sterile; Making
the World GM-Free & Sustainable ), approving the release of these GM potatoes is to subject the
public to serious health risks with potentially harmful effects on wildlife.
We already know that debilitating immune reactions can be triggered by exposure
to the transgenic plant, even in the case of a single gene transfer from bean
to pea, a closely related species [8, 9] (Transgenic Pea that Made
Mice Ill, SiS 29).
Late blight resistance is complex and the fungus versatile
Late blight is one of the most devastating plant diseases. It is caused
by the fungus, Phytophora
infestans, a
pathogen of potato and to a lesser degree tomato. There are many genes involved in blight resistance in potato: four main dominant
genes, R1 to R4, and another seven genes, five of which are alleles (alternative
forms at the same site) of the complex R3 locus.
Hybridisation
with wild Mexican species began in 1909, and continues to the present day.
But in spite of constant efforts to create resistance, the fungus rapidly
developed strains that overcame
the genetic resistance. Chemical fungicides have been developed to control
blight but these too failed to counter the versatility of the fungus. The
fungus has two mating types (A1 and A2) both of which first appeared in Mexico. Only the A1 mating type was present in European potatoes
until 1978 when the A2 mating type appeared in Britain. The presence of the two mating types greatly enhances gene
exchange, accelerating the loss of genetic resistance and fungicide control
[10, 11].
Technology in a hurry
In the early days, resistant potatoes were
obtained using true sexual hybridisation with wild Mexican species
but the resistant strains soon succumbed to mutants of the blight fungus. A wild Mexican species, Solanum bulbocastanum, was stably resistant
to blight but could not be sexually crossed with potatoes. A laboratory procedure
of somatic hybridisation was used to create sexual hybrids; it involves fusing
cells from cell cultures of Solanum bulbocastanum and potato, the fused
cells containing nuclei of both species. When the fused cells undergo cell
division, the chromosomes of the two species become mixed and a single hybrid
nucleus is formed in the cells. The cells can be cultured on solid media to
form a callous (tumour) which when treated with plant growth hormones, produces
plantlets that flower. The somatic hybrids have irregular meiosis (cell division
in forming germ cells during reproduction, which reduces the chromosome number
to half), with irregular chromosome pairing and separation, but relatively
stable blight resistant lines can be obtained [12-14]. Apart from the 11
potato blight resistance genes mentioned earlier, additional genes are involved
in producing broad-spectrum resistance against blight, these
include the gene RB [15], Rpi-blb1
[16] and Rpi-blb 2 [17] which are active in both potato
and tomato. Somatic hybrids are
useful in identifying resistance genes and in transmitting the genes into
potato breeding lines by crossing. Nevertheless, genetic modification of potato
breeding lines is presently preferred, because resistance can be introduced
into commercial lines with greater speed.
No studies done on species-specific processing of transgenic
proteins to rule out immunogenicity or toxicity
The BASF GM potato trials [18-21] involve
two broad-spectrum resistance genes, Rpi-blb1
and Rpi-blb2. These two genes
code for proteins that have a nucleotide-binding site consisting of leucine-rich
repeats (NBS-LRR) typical of a class of regulatory proteins. Many disease
resistance genes code for proteins of that class. Numerous NBS-LRR genes are
present in the typical plant genome, each protein specific for a particular
pathogen, signalling a defence response that frequently involves a localized
cell death (hypersensitive response) [22-24]. The blight fungus suppresses
the potato defence genes in sensitive plants, but is thwarted by successful
defence genes in resistant plants. The NBS-LRR resistance genes in plants
are localized in the cell cytoplasm and do not span the cell membrane but
are activated by signals from pathogens that penetrate into the cell [23,
24]. The cell dies and traps the invading pathogens. Plant NBS-LRR proteins generally produce antibodies when injected into
mammals, but the species-specific processing of the disease resistance proteins,
which contribute to the immune response, has yet to be investigated.
Denial of horizontal gene transfer based on a single research paper exposed
to be fundamentally flawed
The BASF proposals [18-21] indicate that
the potatoes were transformed using two plasmids, each with single copies of the two S. bulbocastanum resistance genes Rpi-blb1 and Rpi-blb2. The two genes were each regulated
by its own endogenous promoter (including an intron as an enhancer) and terminator.
The plasmids also contained a mutant acetohydroxy acid synthetase (ahas)
gene from the tiny mustard plant Arabidopsis
that conferred resistance to the herbicides of the imidazolines group, which
is approved for use in the UK for some
crops, but does not appear to be approved for use with field potato [25].
The ahas gene is controlled by the nopaline synthase
promoter and terminator from Agrobacterium.
The transformed potatoes are herbicide tolerant, but the herbicide is only
used during selection of transformed potato cells, and not during
cultivation of the potato.
Nevertheless,
the herbicide tolerant gene is present in the GM potato and can be transferred,
along with the other transgenes, by cross-pollination, or via horizontal gene
transfer to unrelated species, especially if the GM potato is genetically
unstable, as it may be, as the GM inserts of all commercially approved lines
were found to have rearranged since characterized by the companies [26, 27]
(Transgenic Lines Proven
Unstable, SiS 20 Unstable Transgenic Lines Illegal,
SiS 21). All GM lines intended for the release
contain one or two copies of the plasmid inserts, but no molecular genetic details on the inserts were provided,
nor evidence of genetic stability beyond the bald statement that [19], “The
inserts have been found stable when shoots are propagated via cuttings. Therefore
the inserts are considered to be stably integrated into the nuclear plant
genome.”
BASF dismisses horizontal gene transfer [19] citing an outdated
single reference [28] that one of us has exposed to be fundamentally flawed [29] (Horizontal Gene Transfer – The Hidden Hazards
of Genetic Engineering). Despite the misleading title of the publication
[28] that horizontal gene transfer from the transgenic potato “occurs, if at all, at an extremely
low-frequency”, the actual results showed the opposite was the case. A high transfer frequency of 5.8 x 10-2 per recipient bacterium
was demonstrated under optimum conditions. But the authors then proceeded
to calculate an extremely low theoretical gene transfer frequency of 2.0 x
10-17 under extrapolated “natural conditions”, assuming that different factors acted independently.
The natural conditions, however, were largely unknown and unpredictable, and
even by the authors’ own admission, synergistic effects could not be ruled
out. There is abundant direct and indirect
evidence for horizontal gene transfer reviewed in many ISIS publications
(see recent summary in Living with the
Fluid Genome [30]).
No investigations on immunogenicity or toxicity
The expression of the modifying genes was not studied under extreme conditions
of stress such as drought, water logging, heat, cold, nitrogen excess or starvation
in glasshouse experiments. As
in the past, GM crops have been tested under optimum conditions
for growth prior to commercial or test release into the environment, where
stress conditions may lead to unexpected toxicity (as well as genetic instability)
in GM crops, of which a number of recent cases have emerged [7].
The BASF proposals [18-21] claim that the resistance genes are not expected
to exert any toxic, allergenic or harmful effects on human health arising for
genetic modification, but no feeding trials have been carried out. The genetic
modifications are assumed to be safe because plants contain numerous NBS-LRR
proteins, and cultivated potatoes contain R genes from the wild species S.
demissum. The assumptions of safety are specious. The S. demissum
genes in commercial potatoes are NBS-LRR genes, but are not the broad-spectrum
NBS-LRR genes used in the BASF potatoes. Above all, the finding that gene transfer
between related species may nevertheless lead to proteins with powerful immune
responses [8, 9] need to be taken on board. The current procedure used to scan
amino acid sequences of proteins for epitopes (motifs) that elicit allergic
responses (involving IgE) would overlook the powerful immune responses resulting
from carbohydrate chains added during processing of the proteins. The GM potatoes
must be tested not only for allergenicity, but also for inflammatory and other
immune responses, and proven safe before being released into the environment.
Otherwise, the impacts on humans, livestock and wildlife could be devastating.
Assumptions of safety not justified on existing evidence
BASF had petitioned for field test release of the GM potatoes beginning
2005 in the Netherlands. The notice of petition indicated that
the GM potato would be released in Germany, United Kingdom and Sweden but
full reports of the tests were not provided [31]. In the United States, there
have been five field tests with the GM potatoes in Minnesota and Wisconsin,
carried out by USDA or the University of Minnesota [32]. The isolation and
deployment of the RB genes in potato has been described [33, 34].
Field-testing of broad-spectrum
NBS-LRR genes has begun with the potato blight resistant strains. Broad-spectrum
pest-resistant strains of rice, maize, soybean, and numerous food crops will
soon follow. It is imperative that the safety of these genetic modifications
to health and the environment be fully evaluated before the GM crops are released
in field trials. The proposition that the NBS-LRR family of plant pest resistance
genes and their products are safe
for humans and for the environmental because they are found in food crops and hence require no
further testing is simply not justified on the basis of existing evidence.
The UK government must withdraw permission for the trials, or else
the regulators should be held responsible for any harm caused.
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