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Modern Genetic Analysis Chapter 11. Applications of Recombinant DNA Technology Recombinant DNA Technology in Eukaryotes
Genetics In Process 11-1: Transgenic crop plants

In November 1996, several British newspapers ran front-page photographs of inflatable rafts belonging to the Greenpeace organization blocking the entry of a freighter into Liverpool harbor. Nearby, Greenpeace had erected a huge banner on a barge, showing the words "Floodgate: Genetic Pollution." The protest was against the first shipment of genetically engineered soybeans from the United States to Britain. In the next month, Greenpeace was in Hamburg harbor, Germany, using a powerful slide projector to beam the words "Genetic experimentdon't buy it" onto the side of a similar freighter. The soybeans contained a bacterial transgene that conferred resistance to a weedkiller called glyphosate, inserted so that fields of crops could be sprayed and easily kept weed free. The advantages to the farmer are obvious, inasmuch as weeds are a considerable problem in agriculture. The objection of the protesters to such transgenic plants was that the transgenes might be deleterious to human health. One concern is possible allergic reactions to the transgene's protein product. The company that developed the soybeans claimed that there was no danger, and this view was supported by regulatory agencies. Another fear was that as a result of the crop being resistant, consumers might be exposed to higher levels of herbicides. An additional concern was that the engineered plants might escape and introduce the transgenes into related species.

Whether these objections are valid or not, the reference to a "floodgate" in the Greenpeace banner was correct because transgenic crops are flooding into farms and hence into the marketplace. It is projected that, in 1998, transgenic plants of corn, soybeans, and rapeseed will be planted in 20 times the acreage of 1996. The fact is that this new technology has immense potential benefit. What are some other examples? Another age-old problem in farming is crop destruction by insects. The bacterium Bacillus thuringensis contains 96 genes for delta endotoxins, proteins that punch holes in the gut of insect larvae. These proteins are called Bt toxins. The Bt toxin genes, when introduced into plants next to a powerful plant promoter, confer resistance to specific insect pests. For example, a certain Bt gene makes corn resistant to one of its most devastating insect pests, the European corn borer. This type of resistance is particularly desirable because it is specific; it has no adverse effects on people, on other mammals, or on harmless insects. Bt toxin genes, like the genes for glyphosate resistance, are inserted into the plant genome by using the T-DNA method. Millions of acres of corn, cotton, and potatoes bearing Bt toxin genes are currently under cultivation in North America.

Another area of great promise is "molecular farming," making transgenic plants that contain health-care products such as pharmaceuticals and vaccines. Plants containing vaccines are particularly important for developing countries because the vaccines are inexpensive, orally administered without specialized techniques (possibly eating one seed is all that is necessary), and easy to deliver to remote areas (vaccines currently require refrigeration and often decay en route).

© 1999 by W. H. Freeman and Company. All rights reserved.