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

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.

© Promoter © Marker gene © Desired gene © Terminator

T-vector

ENVIRONMENTAL RISKS Random insertion of transgene and high

expression levels

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 transfer from the transgenic plants may spread the novel genes and gene-constructs to unrelated species-microbes 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…

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

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.)

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

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)

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

Increased resistance to herbicides, leading to super-weed 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

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.

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

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)

Monsanto's transgenic soya has a 26.7% increase in a trypsin-inhibitor 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

Efficient and specific gene targeting to cells

Stable, single integration of gene at defined site

Normal levels of expression of desired gene

Proven safety

X The GMO crops on the market fulfill none of these criteria

Future of biotechnology

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

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