Transcript GMOs: Scientific Evidence

GMO release: Scientific Sense?
Dr. William H.L Stafford,
Advanced Research Center for
Applied Microbiology,
Department of Biotechnology,
University of the Western Cape.
GMOs and breeding
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We have been modifying our food sources for
thousands of years, selecting for favourable
characteristics. These breeding techniques rely on
fertlization by cross-pollination of the same species
Biotechnology has provided us with the tools to
engineer a a plant with any chosen characteristic.
Species barriers can be crossed- we can take a
gene from one organism and place it in another
totally unrelated organism and create transgenics.
Genetic engineering of plants
GM crops
>90% of GM crops
are engineered with
transgenes for
herbicide
resistance and
insecticides.
T-vector
© Promoter © Marker gene © Desired gene © Terminator
ENVIRONMENTAL RISKS
Random insertion of transgene and high
expression levels
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Genetic pleiotropic effects result from abnormal expression
levels, position effects of inserted genes and secondary
mutations.
The CaMv is a strong promoter providing a high level of gene
expression. All living organisms that interact with the transgenic
plant are exposed to high levels of the expressed transgene.
The insecticidal Bt-toxins, isolated from Bacillus thuringiensis,
are often engineered into plants. Lacewings fed on aphid pests
that had eaten Bt-maize took longer to develop and were two to
three times more likely to die. (Birch, A.N.E., et al. 1997, Soft Fruit and
Perennial Crops and Marvier, M. 2001. Ecology of transgenic crops. American
Scientist)
Insecticidal toxins from transgenic plants can kill beneficial
(non-target) species and be passed higher up the food chain
Effects on biodiversity and evolution
Genes can spread from transgenic plants by ordinary cross
pollination to nontransgenic plants of a related species, and
also by horizontal gene transfer to unrelated species.
 The most obvious effects of cross-pollination already identified
are in creating herbicide-tolerant, or insecticidal weeds and
superweeds. Studies with oilseed rape (Brassica napus) have
shown that the Bt gene can be passed on to a wild, weedier
relative (Brassica rapa) (Halfhill, M.D., et al. 2002. Environmental
Biosafety Research).
 Another hazard is the spread of the antibiotic resistance
marker genes which are in a high proportion of transgenic
plants.
There are unpredictable physiological impacts on the organisms to which
the genes and gene-constructs are spread and hence on the ecological
environment.
Horizontal gene transfer has been relatively rare in our evolutionary
past, due to natural species barriers prevent gene exchange,
and mechanisms which inactivate or break down foreign DNA
Horizontal transfer from the transgenic plants may spread
the novel genes and gene-constructs to unrelated speciesmicrobes in the soil, worms, insects reptiles, birds, small
mammals and human beings.
Agrobacterium vector system allows facilitated means of
gene escape.
 Increased horizontal gene transfer in the soil rhizosphere and
seeds have been noted (Sengelov et al. 2001. Current Microbiology.)
 The Ti plasmid of the Agrobacterium has mobile genetic
elements elements to integrate into the plant DNA. This
integration is random and subjected to further recombination…
Gene transfer and escape
Both the Ti vector and the CaMv promoter have palindromic
sequence that are recombination hotspots and subjected to
increase horizontal gene transfer (Kohli et al. 1999, Plant.J.)
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This recombination with other DNA can lead to:
Reactivation of dormant viruses and the generation of new
viruses
Generation of new bacterial pathogens and the spread of drug
and antibiotic resistance marker genes among pathogens
Insertion of genes into cells of recipient species, mutagenesis
and cancer transformation.
Such elements have increased penetrance into the environment
(especially with selection) and can outcross other varieties
Outcrossing
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Transgenic A. thaliana plants were roughly 20 times more likely
to outcross. These results show that genetic engineering can
substantially increase the probability of transgene escape.
(Bergelson, J. et al. 1998. Nature)
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Transgenic DNA introgressed into traditional maize landraces in
Oaxaca, Mexico (Quist D and Chapela IH. Nature 2001)
Horizontal gene transfer from one species to another may be a
major factor in evolutionary change! (Syvanen, M. 1986. Trends In
Genetics)
Summary: environmental risks
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Increased resistance to herbicides, leading to superweed characteristics
Increased spread of antibiotic resistance
Reduced biodiversity due to outcrossing and
selection
Increased occurrence of cancers caused by
insertional mutagenesis and position effect changes
in gene expression.
Unpredictable effects on genetic evolution and
ecosystem function
HEALTH RISKS:
DNA stability
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DNA can persist in the soil where transform a range
of organisms. Transgenes will be able to spread to
bacteria and viruses, spreading antibiotic resistance
genes among the pathogens.
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DNA is not completely broken down in the gut.
Genes can spread from ingested transgenic plant
material to bacteria in the gut and also to cells of the
organism itself. Antibiotic resistant marker genes
from genetically engineered bacteria can be
transferred to indigenous bacteria (Netherwood T, et al.
Technical report on the Food Standards Agency project G010008)
Expected and unexpected toxicity
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Transgenic potatoes expressing GNA insecticide (“Snowdrop”,
Galanthus nivalis, lectin) fed to rats resulted in increase in
intestinal mucosal thickness and T-lymphocyte infiltration. (Erwin
S.W.B.and Putzai A. 1999 Lancet)
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Monsanto's transgenic soya has a 26.7% increase in a trypsininhibitor and has been sown to inhibit the growth rate of male
rats. This raises the possibility that transgenic soya is
responsible for the reported recent increase in soya allergy.
Human gene therapy experiments for severe combined
immunodeficiency (SCID) caused by the absence of the
enzyme adenosine deaminase (ADA) were halted by the FDA
after a second treated child died of cancer.
Required features for release of a GMO
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Efficient and specific gene targeting to cells
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Stable, single integration of gene at defined site
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Normal levels of expression of desired gene
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Proven safety
X The GMO crops on the market fulfill none of these criteria
Future of biotechnology
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It is important to distinguish between contained use
of transgenic organisms and their release to the
environment.
It is vital that GMO crops are proven safe for through
proper independent, long-term feeding trials and
environmental impact assessments
It is essential to monitor GMOs since they have been
released and we need to observe the effects of this
experiment
References
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 Kohli A.,Griffiths S, Palacios N, Twyman R, Vain P, Laurie D and Christou P. (1999) Molecular characterization of transforming plasmid
rearrangements in transgenic rice reveals a recombination hot spot in the CaMV 35S promoter and confirms the predominance of microhomology
mediated recombination" Plant.J. 17,591-601.
 Sengelov G, Kristensen KJ, Sorensen AH, Kroer N, and Sorensen SJ. Effect of genomic location on horizontal transfer of a recombinant gene
cassette between Pseudomonas strains in the rhizosphere and spermosphere of barley seedlings. Current Microbiology 2001, 42, 160-7.
 George A. Kowalchuk, Maaike Bruinsma and Johannes A. van Veen. Assessing responses of soil microorganisms to GM plants TRENDS in
Ecology and Evolution Vol.18 No.8 August 2003
 Bergelson, J., Purrington, C.B. and Wichmann, G. (1998). Promiscuity in transgenic plants. Nature 395, 25
 Quist D and Chapela IH. (2001) Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico. Nature, 414, 541-3, 2001
 Syvanen, M . 1986. Cross-species gene transfer: a major factor in evolution? Trends In Genetics pp 1—4
 Hilbeck, A., Baumgartner, M., Fried, P.M. and Bigler, F. (1997). Effects of transgenic Bacillus thuringiensis-corn-fed prey on mortality and
development time of immature Chrysoperla carnea (Neuroptera: Chrysopidae). Environmental Entomology
 Halfhill, M.D., R.J. Millwood, P.L. Raymer, and C.N.Stewart, Jr. 2002. Bt-transgenic oilseed rape hybridization with its weedy relative, Brassica
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 Hilbeck, A., Baumgartner, M., Fried, P.M. and Bigler, F. (1997). Effects of transgenic Bacillus thuringiensis-corn-fed prey on mortality and
development time of immature Chrysoperla carnea (Neuroptera: Chrysopidae). Environmental Entomology 27, 480-487.
Vaden V.S. and Melcher, U. (1990). Recombination sites in cauliflower mosaic virus DNAs: implications for mechanisms of recombination. Virology
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 Sengelov G, Kristensen KJ, Sorensen AH, Kroer N, and Sorensen SJ. (2001) Effect of genomic location on horizontal transfer of a recombinant
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 Ewen S. W. B, and Pusztai,A. (1999) Effect of diets containing genetically modified potatoes expressing Galanthus nivalis lectin on rat small
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 Netherwood T, Martin-Orue SM, O'Donnell AG, Gockling S, Gilbert HJ and Mathers JC. Transgenes in genetically modified Soya survive passage
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