ScienceWeek

5. GM FOOD: RISKS AND OPPOSITION

GENOMICS, GENETIC ENGINEERING, AND DOMESTICATION OF CROPS

The following points are made by Steven H. Strauss (Science 2003 300:61):

1) Genomic sequencing projects are rapidly revealing the content and organization of crop genomes (1). By isolating a gene from its background and deliberately modifying its expression, genetic engineering allows the impacts of all genes on their biochemical networks and organismal phenotypes to be discerned, regardless of their level of natural polymorphism. This greatly increases the ability to determine gene function and, thus, to identify new options for crop domestication (2). The organismal functions of the large majority of genes in genomic databases are unknown.

2) At the same time, however, government regulatory regimes are making field studies of genetically engineered (GE) plants needed to understand gene function in the context of normal plant development increasingly difficult. These regimes have been created largely because of biosafety issues raised by genes imported from distant species. However, they have been applied to asexually introduced genes whose source and effects resemble those of traditional breeding. This imposes large costs that impede the delivery of public benefits from genomics research.

3) The first wave of widely planted transgenic crops expressed traits that were encoded by exogenous (bacterial or viral) gain-of-function genes such as those for herbicide or pest resistance. Their action depended on the solitary effects of single proteins that were virtually independent of plant metabolism. By transferring functions between phylogenetically divergent organisms, these genes imparted traits that could not be readily obtained from traditional breeding. This created transgenic plants with very high agronomic and environmental value but also raised difficult questions because of their ecological and evolutionary novelty (3).

4) In contrast, genomics-guided transgenes (GGT) will increasingly be based on native or homologous genes from related species. Such genes will often modify metabolism in a manner similar to that of natural or induced mutations, but it should be possible to create desired phenotypes with greater precision and efficiency. Dominant alleles important to agricultural goals, but poorly represented in breeding populations because they are rare or deleterious to wild progenitors, can be created and inserted into varied kinds of germplasm. Traits that have already been genetically engineered in this manner include diverse modifications to plant reproduction, stature, and lipid and lignocellulose chemistry. The improvements achieved via GGTs should be comparable to or of greater value than those obtained via traditional breeding approaches that have achieved wide public acceptance, and have been free of calls for government regulation.

5) The author concludes: Regulations that distinguish between classes of recombinant plants may decrease some public condemnation of agricultural genetic engineering. If regulatory costs and hurdles were significantly reduced, it might promote genetically engineered crop development by small companies and public sector investigators. Given the widespread suspicion of the power and ethics of many large corporations, and the major role that this social skepticism has played in the controversy over genetically engineered crops, such "democratization" of biotechnology might be as important as biological advances in promoting public approval of genetic engineering in agriculture.(4,5)

References (abridged):

1. J. Bennetzen, Science 296, 60 (2002).

2. "Domesticate--to train or adapt (an animal or plant) to live in a human environment and be of use to humans" from American Heritage Dictionary (Houghton Mifflin, New York, 1982).

3. L. L. Wolfenbarger, P. R. Phifer, Science 290, 2088 (2000).

4. M. L. Siegal, A. Bergmann, Proc. Natl. Acad. Sci. U.S.A. 99, 10528 (2002).

5. T. H. Chen, N. Murata, Curr. Opin. Plant Biol. 5, 250 (2002).

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ASSESSING THE RISKS ASSOCIATED WITH NEW AGRICULTURAL PRACTICES

The following points are made by R.S. Hails (Nature 2002 418:685):

1) The improvement of crop varieties through plant breeding has greatly increased yields over the past few decades. This in turn has reduced the area of land that would otherwise have been dedicated to agriculture as a result of an increasing world population(1). But these new crop varieties have been accompanied by changes in agronomic practice, which have included increased use of fertilizers, pesticides and irrigation. Many of these changes have been to the detriment of wildlife(2). Change has therefore brought both benefits and costs, and the future of food is linked inextricably with the future of the environment.

2) Risk assessment of GM plants has been divided traditionally into direct and indirect impacts. Direct impacts arise from the presence of the transgenic plant itself, or the consequences of transfer of the transgene into wild relatives. Indirect impacts arise from the management practices associated with the transgenic crop. Ecological theory has an important role to play in assessing such impacts.

3) The potential direct impacts of a GM plant include any changes in ecological fitness which may make the crop plant or any crop plant/wild relative hybrids more invasive (3). Invasive species represent one of the greatest threats to biodiversity(4,5). Most non-native species are harmless, but a few become invasive and detrimental to indigenous ecosystems. Japanese knotweed (Fallopia) and rhododendron (Rhododendron ponticum) are notable examples in the UK, while yellow star thistle (Centaurea solstitalis) and European purple loosestrife (Lythrum salicaria) are particularly disruptive examples in the US. Most of these invasive species originate from horticulture, and so far there is no evidence that any GM crop plant is significantly more invasive than its conventional counterpart.

4) Nevertheless, the possibility exists that certain transgenic plants could pose a direct threat through enhanced ecological fitness. In particular, transgenes that confer enduring resistance to pathogens could cause ecological release in wild relatives if populations are regulated by those same pathogens. Indeed, the ethos behind biological control relies on this principle, in that it assumes that some plants become weeds because they have escaped their natural enemies, and seeks to reduce populations by the introduction of a suitable pathogen or herbivore. Wild plant populations contain a variety of resistance genes that have evolved in response to the presence of pathogens. But genetic modification greatly widens the pool of potential resistance genes, allowing the use of new pathogen-resistance mechanisms. The use of viral coat protein genes to provide resistance against the same viral strains is a case in point. Such resistance mechanisms may prove to be more enduring than those produced by conventional plant breeding. Although this is good news for agriculture, the potential for causing ecological release in wild populations should be considered.

References (abridged):

1. Conway, G. & Toenniessen, G. Feeding the world in the twenty-first century. Nature 402, C55-C58 (1999)

2. Krebs, J. R., Wilson, J. D., Bradbury, R. B. & Sirwardena, G. M. The second Silent Spring? Nature 400, 611-612 (1999)

3. Crawley, M. J., Hails, R. S., Rees, M., Kohn, D. & Buxton, J. The ecology of transgenic oilseed rape in natural habitats. Nature 363, 620-623 (1993)

4. Sala, O. E. et al. Global biodiversity scenarios for the Year 2100. Science 287, 1770-1774 (2000)

5. Trewavas, A. J. & Leaver, C. J. Is opposition to GM crops science or politics? EMBO Rep. 2, 1-5 (2001)

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POTENTIAL ADVERSE HEALTH EFFECTS OF GENETICALLY MODIFIED CROPS

The following points are made by A. Bakshi (J Toxicol Environ Health B Crit Rev. 2003 6:211):

1) Genetically modified crops have the potential to eliminate hunger and starvation in millions of people, especially in developing countries because the genetic modification can produce large amounts of foods that are more nutritious. Large quantities are produced because genetically modified crops are more resistant to pests and drought. They also contain greater amounts of nutrients, such as proteins and vitamins. However, there are concerns about the safety of genetically modified crops. The concerns are that they may contain allergenic substances due to introduction of new genes into crops. Another concern is that genetic engineering often involves the use of antibiotic-resistance genes as "selectable markers" and this could lead to production of antibiotic-resistant bacterial strains that are resistant to available antibiotics. This would create a serious public health problem. The genetically modified crops might contain other toxic substances (such as enhanced amounts of heavy metals) and the crops might not be "substantially equivalent" in genome, proteome, and metabolome compared with unmodified crops. Another concern is that genetically modified crops may be less nutritious; for example, they might contain lower amounts of phytoestrogens, which protect against heart disease and cancer.

2) The author concludes that a review of available literature indicates that the genetically modified crops available in the market that are intended for human consumption are generally safe; their consumption is not associated with serious health problems. However, because of potential for exposure of a large segment of human population to genetically modified foods, more research is needed to ensure that the genetically modified foods are safe for human consumption.

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THE ECOLOGICAL RISKS AND BENEFITS OF GENETICALLY ENGINEERED PLANTS

The following points are made by L.L. Wolfenbarger and P.R. Phifer (Science 2001 292:638):

Discussions of the environmental risks and benefits of adopting genetically engineered organisms are highly polarized between pro- and anti-biotechnology groups, but the current state of our knowledge is frequently overlooked in this debate. A review of existing scientific literature reveals that key experiments on both the environmental risks and benefits are lacking. The complexity of ecological systems presents considerable challenges for experiments to assess the risks and benefits and inevitable uncertainties of genetically engineered plants. Collectively, existing studies emphasize that these can vary spatially, temporally, and according to the trait and cultivar modified.

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WORLDS APART? THE RECEPTION OF GENETICALLY MODIFIED FOODS IN EUROPE AND THE US

The following points are made by G. Gaskell et al (Science 1999 285:384):

1) An international study of biotechnology in the public sphere (1) sheds some light on why genetically modified (GM) foods are so much more controversial in Europe than in the United States. The authors compare public perceptions of five applications of modern biotechnology and look for explanations for the differences between Europe and the United States in terms of media coverage, trust in the regulatory process, and scientific literacy.

2) In October 1996 a representative sample survey (about 1000 respondents per country) was conducted in all 15 member states of the European Union, together with Norway and Switzerland (henceforth "Europe"). The key questions were also used in a U.S. survey in late 1997 (2). These surveys were conducted 2 to 3 years ago and over a period of roughly a year; hence, the data provide a historical snapshot of public perceptions in 1996-1997. Of course, with the rapid advance of food biotechnologies and other developments in the life sciences (such as the cloning of Dolly the sheep), one would not expect to find the same opinions and attitudes in 1999. But the use of similar questions in the surveys makes it possible to look at comparative structural differences in the pattern of public perceptions that may hold clues to understanding the situation in 1999.

3) Respondents were asked whether they thought each of five biotechnologies -- genetic testing, GM medicines, GM crops, GM food, and xenotransplantation (GM animals for use in human transplantation) -- was useful, risky, morally acceptable, and to be encouraged (2).

4) People in Europe and the US showed varied levels of support across the different applications. GM medicines and genetic testing received the most support, GM crops and GM foods received intermediate support, and xenotransplantation received the least support. There was not always strong support for biotechnology in the US; for example, the average US respondent was opposed to xenotransplantation. Moreover, US respondents were not always more supportive than European respondents; for example, Europeans were more supportive of genetic testing, whereas people in the United States were significantly more supportive of GM crops and GM foods than were people in Europe.

5) In conclusion, no single explanation accounts for the greater resistance to food biotechnology in Europe. Various factors are implicated and interrelated. Different histories of media coverage and regulation go together with different patterns of public perceptions, and these in turn reflect deeper cultural sensitivities, not only toward food and novel food technologies but also toward agriculture and the environment. This raises the following question: How should science, industry, and governments respond?(3-5)

References (abridged):

1. J. Durant, M. W. Bauer, G. Gaskell, Eds., Biotechnology in the Public Sphere: A European Source Book (Science Museum Publications, London, 1998).

2. Eurobarometer Survey: www.sciencemag.org/feature/data/991913.shl

3. P. E. Converse, in Ideology and Discontent, D. E. Apter, Ed. (Free Press, New York, 1964), pp. 206-261

4. H. Schumann and S. Presser, Questions and Answers in Attitudes Surveys: Experiments in Question Form, Wording and Context (Academic Press, San Diego, CA, 1981).

5. P. J. Leahy and A. Mazur, Soc. Stud. Sci. 10, 259 (1980)

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