New Zealand Treecrops Association

Knowledge - General

GM technology: risks and benefits

By Simon Deroles Ph.D, who has been producing transgenic plants in New Zealand for 18 years and currently works in the Plant Pigments team, Crop & Food Research, Palmerston North.

I hope to clarify some of the misconceptions about GM technology. GM technology is by no means risk free nor will it save the world. On the other hand it is a very powerful technology and its use has the potential to alleviate many of the problems endemic in the way we practice industrialized agriculture (e.g. pesticide use, excess nutrient runoff, drought resistance, nutrient content). In general, a genetically modified plant can be defined as a plant that would not arise without human assistance. It carries a genetic makeup that has DNA from another plant or organism that it could not naturally cross hybridise with. Mankind has been generating GM plants for hundreds of years. A hybrid plant, generated by a forced cross between two different species, results in the mixing of two entire specie's genomes. Recently such crosses have been achieved through: embryo rescue, e.g. Potato (Ramon & Hanneman, 2002), Cucumber (Chen et al. 2002), and Kiwifruit (Hirsch et al. 2001): cell fusion, where two plant cells from different species are fused in the test tube, e.g. Potato (Oberwalder et al. 1997): and induced mutagenesis by exposure to chemicals or radiation, e.g. fruit species (Predieri 2001), chrysanthemum (Mandal et al. 2000), and legumes (Micke 1993). Many of our grains, vegetables and ornamental crops would not exist without the use of these techniques.

The most recent addition to this array of techniques is "Specific Gene Integration", commonly referred to as GM technology, which represents a major addition to our tools for making new plants. It has three primary differences from existing techniques. Firstly, the total number of genes altered using GM is a fraction of the number of genes altered or moved using the older GM techniques described above. Secondly, with the new GM methods we know exactly what DNA we have altered and where it has gone in the new plant. None of this information is available when we use the older techniques. Finally the new GM methods enable us to specifically transfer DNA from any source, rather than only from other plants.

There are two ways in which GM plants are generated. The first and most common way is via the use of nature's own "genetic engineer" called Agrobacterium tumefaciens (Zupan et al. 2000). This is a soil bacterium that has evolved the ability to transfer genes into plant cells, resulting in the formation of a gall in the plant stem. Scientists have discovered that they can replace the genes that cause the galls with any other gene for transfer to the target plant. The modified bacteria are used to infect a plant cell and plants are then regenerated using common tissue culture techniques.
The second method uses a variety of techniques to directly introduce the DNA into the plant cell where it is taken into the plant genome (Lai and Lai 1993). In both techniques the plant itself carries out the actual process of integrating the DNA into the plant genome.

Risks

The perceived risks from GM plants are numerous and include: contaminated food, super weeds, horizontal gene transfer and many more. All these risks centre around three subjects. Firstly, how does a GM insertion event affect the host plant; secondly, what effect does the introduced gene have; and finally how likely is it that the insertion event will spread to other organisms.

GM techniques result in one or more insertion events at random points in the plant genome. There is concern that the inserted DNA could interrupt an existing gene. This is indeed possible, but because we know the sequence of the inserted gene we can trace where it has gone and check for insertional mutations. In existing breeding techniques the number of genetic rearrangements can be many times greater. What's more, we have no knowledge of the DNA rearrangements nor the genetic makeup of the final plant. As a result it is almost impossible to determine what rearrangements have occurred and what effect they will have. The new GM technology enables us to analyse the resultant plants to a far greater degree than do existing methods. Surely this results in a lower level of risk from insertional mutation and rearrangements, rather than a higher one.

The greatest level of risk in the new GM technology derives from the DNA we can insert. DNA carries the genetic information that determines the characteristics of almost every living organism. The physical structure of the DNA molecule is identical in all living organisms. Different genes are merely defined by the order of the four nucleotides that make up the DNA molecule. Recent research has shown that huge numbers of genes are almost identical in their code across a wide range of species. Unlike previous methods GM technique enables us to insert DNA from any living source. This vastly increases the amount of variation we can generate. This makes the technology very powerful, but it also means we must take care what gene(s) we insert. As a result, the real risk from this technology is not the technique itself, which is considerably more precise than previous methods, but rather the products we generate. In other words instead of banning the technology, we should ensure that there is a robust process for the analysis and approval of new products prior to their commercial release. This is essential if we are to use this technology with an acceptable degree of safety.

The final major area of risk is the likelihood that the new gene will spread to other organisms. This can occur by simply crossing with wild relatives in the field or by transfer to other organisms via a process commonly termed "horizontal gene transfer" or HGT. Gene spread by crossing to wild relatives is a potential problem regardless of whether the new plants are generated via natural breeding or by GM techniques. This issue needs to be taken into account when deciding to introduce a plant into a new area e.g. what is the proximity of wild relatives? This requires a careful assessment of the product and where it can be grown. HGT is the process whereby the new gene is transferred from the original organism to another, e.g. from a plant to a bacterium. HGT is a natural process and has been responsible for the transfer of genes from bacteria and viruses to plants, animals, fungi and insects over millions of years. Although it occurs in nature, the frequency is low. A concern with transgenic plants is the transfer of the new genes to bacteria in the soil or in our intestines, from broken down plant matter, or even transfer of the plant genes directly to us through eating them. Interestingly, studies on the human genome can find no evidence of the transfer of plant genes to humans through eating plants. Since we have been eating plants for millions of years, the chances of this occurring seem fairly low. It is more likely that bacteria could acquire plant genes. However, analysis of bacterial genomes can find no evidence that they contain plant genes either. There is still much work to be done on this subject (see http://www.genok.org), but current evidence indicates that the rate of HGT from plants to other organisms is very low and will not be increased by the use of GM technologies (Prins & Zadoks 1994; Clarke 2002).

The Myths

There have been a number of items in the media about harm caused by GM products. Much of this reporting has been based on scant information and often the converse conclusion is the correct one. With butterflies and Bt the initial report on this topic exclaimed that the Bt toxin (used by organic farmers) kills monarch butterfly caterpillars and thus the vast acreages of transgenic Bt corn crops in the USA will destroy the monarch butterfly. The story was based on lab results, which showed that the Bt toxin could kill monarch caterpillars. This was not surprising as the caterpillars are related to other insects susceptible to this compound. However, there is a big difference between a lab result and what actually happens in the field. Several multi-year field studies have shown that the amount of pollen consumed by the caterpillars in the field was too small to have any effect (Gatehouse et al. 2002). In fact, the use of this corn means the farmer only has to use one application of insecticide instead of 15 for a non-GM crop. The result of this is an increase in populations of non-target insects that normally fall victim to traditional insecticide sprays. In addition, a dramatic decrease in insecticide sprays also leads to reduced soil and groundwater contamination and better health of farm workers. For a summary of Bt corn see Ostlie et al. (1997).

Herbicide Resistance

In New Zealand an application to field trial roundup resistant canola was withdrawn due to the intense public opposition aroused by reports of the harm this could do due to increased herbicide use. What the reports failed to disclose was that weeds in some canola crops are already controlled by herbicides, since canola has been naturally bred for resistance to the herbicide Atrazine (Dept of Ag. WA: Bulletin 4411, 2001). Atrazine has an extended soil life and repeated use over several seasons leads to a build up in the soil and groundwater (Wolf and Nowak 1996). Roundup has a soil lifetime of approximately 3 hours. So in fact, using Roundup for weed control in canola crops is better for the environment than current herbicide-based weed control practices.

Now that significant areas of GM crops have been grown on a commercial basis for six years some of the benefits of this technology are emerging. Most of the GM crops in the world are grown in the USA; 75 per cent of the US soybean crop in 2002 is GM and is mostly Roundup resistant (Padgette et al. 2002). Because of the use of Roundup to control weeds, 48 per cent of these farmers have eliminated tillage altogether. This has reduced topsoil loss by 247 million tons and saved the use of 234 million gallons of fuel (Dennis 2002). In 2001, GM crops in the USA reduced pesticide use by 21 million kilograms and production costs by US$1.2 billion, and increased production by 1.8 million tonnes (Fraley 2002). In China, GM cotton has reduced insecticide use by 80% (Huang et al. 2002). In 1992, the Hawaiian papaya industry was almost wiped out by the ringspot virus. A GM virus-resistant papaya line developed by researchers at Cornell and Hawaii Universities saved the entire industry (Ferreira et al. 2002). For a convenient summary of the role of biotech crops in the US see Nill (2002).

These are just some of the benefits arising from the use of GM crops. To date the principal benefactors of this technology have been farmers but we all benefit from reduced pesticide use and farming practices that conserve the world's soil.

In the medical field a number of pharmaceutical products have been made using GM organisms for many years. For example, insulin, growth hormones, heart disease medication, anticancer drugs and cystic fibrosis medication are all produced by genetically modified animal cells or bacteria in large bioreactors (e.g. Biogen at www.Biogen.com).

The Future

There are many new crops under development to address a variety of needs. Professor Ingo Potrykus is developing GM rice plants with elevated levels of vitamin A precursors to alleviate blindness in the third world. In addition, he is developing rice with increased iron and protein content to combat malnutrition (King 2002). GM crops are being developed to improve processing quality, produce pharmaceuticals such as edible vaccines and antibodies, and produce raw materials for the plastics industry to reduce our dependence on petrochemicals. Advances in the technology will lead to the generation of GM plants without selective marker genes (e.g. antibiotic resistance genes) and plants with genes targeted to a specific tissue and time of expression.

With the exception of papaya, none of the examples presented here are tree crops. Due to the long maturity times for tree crops it will be some time before such GM crops are in commercial production. There is much research in the timber industry on developing woods for increased strength, durability and pulping quality. Poplar and pine trees are examples of timber crops that can be transformed (Walter 2002; Delledonne 2001). There is also considerable effort going into developing transgenic fruit trees (e.g. apple) for improved post-harvest quality, flavour, disease resistance and appearance.

There are indeed risks associated with this technology. However, to date these risks have not been problematic, in spite of the fact that the total GM crop area is now close to 300 million acres worldwide. The commercial release of transgenic tree crops is only a matter of time with the first generation primarily addressing disease resistance and wood quality. What has become plain is that these crops can and will provide real and tangible benefits. Continued safe use of this technology relies on the effective analysis and regulation of each product as it is developed.

From The Tree Cropper, Issue 32, November 2002

References

Crop	Subject	Reference
Allocasuarina verticillata	Transformation method	Tranche etal. 1997
Apple: Royal Gala (Malw x domestica)	Transgene stability	Yaoetal. 1999
Apricot (Prunus armeniaca)	Virus resistance	Machadoetal. 1994
Aspen Populus tremula	Transgene stability	Kumar & Fladung 2002
Casaurina (Casuarina glauca)	Transformation method	Le et al. 1996
Jin Orange Citrus sinensis	Bacterial resistance	Chen et al. 1997
Lime (Citrus aurantiifolia Swing.)	Transformation method	Penaetal. 1997
Native and landscape Trees	Pest and disease resistance	Adams et al. 2002
Papaya Carica papaya	Virus resistance	Ferreira et al. 2002
Persian walnut (Julgans regia L.)	Transformation method	Escobar et al. 2000
Pine (Pinus radiata)	Review	Walter et al. 2002
Plum (Prunus domestica)	Virus resistance	Machado et al. 1994
Ponkan Mandarin (Citrus reticulata Blanco	Seedless fruit	Li et al. 2002
Poplar Populus alba	Insect resistance	Delledonne et al. 2001
Rubber tree (Hevea brasiliensis)	Recombinant proteins	Arokiaraj 2000
Shatian pummelo (Citrus grandis)	Bacterial resistance	Chenetal. 1997
Sour Orange (Citrus aurantium L.)	Virus Resistance	Gutierrez et al. 1997 Ghorbel et al. 2000
Transgenic forest trees	Review	Merkle & Dean 2000
Transgenic trees	Plant physiology	Herschbach & Kopriva 2002
Transgenic trees	Review	Pena & Seguin 2001
Trifoliate Orange (Poncirus trifoliate Raf.)	Transformation method	Kaneyoshi et al. 1994
Xinhui or Sweet Orange (Citrus sinensis)	Bacterial resistance	Chenetal. 1997 Pena et al. 1995

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Created: 2003 Jun 27 - Modified: 2007 December 18