Transgenic plants are plants that have been genetically engineered, a breeding approach that uses recombinant DNA techniques to create plants with new characteristics. Transgenic plants are produced by adding one or more genes to a plant’s genome, by a process called transformation. They are identified as a class of genetically modified organism (GMO). Transgenic plants have been developed for a variety of reasons: longer shelf life, disease resistance, herbicide resistance, and pest resistance. The first transgenic crop approved for sale in the US, in 1994, was the FlavrSavr tomato, which was intended to have a longer shelf life. Today, there are more than 10,677,000 km² of transgenic plants being grown throughout the world. There are four general types of transgenic plants: those with genes to improve the quality of the product, those with genes to allow them to resist disease or herbivory (consumption by herbivores, usually insects), plants with genes that allow them to be resistant to the effects of specific herbicides, as well as plants with genes conferring resistance to harsh environmental conditions (extremes of cold, heat, drought,salt concentration, etc.) A developing group of transgenic plants is that of nutraceuticals, or plants designed to possess properties that make them healthier in specific ways. Examples include plants that produce higher concentrations of specific compounds like lycopene or beta carotene (see Golden rice). An emerging class of transgenic plant, sometimes known as pharmacrops, aims to use plants to manufacture other products, such as pharmaceuticals and industrial chemicals. Testing of a variety of these crops has been underway for several years. It appears that no such products have yet been used in the commercial market. Transgenic crops are grown world wide, although the greatest concentration of transgenic crops is in the United States, at 63% of the world total in 2003. At that time, 81% of the soybeans, 73% of the cotton and 40% of the corn being grown were transgenic. At that time most of the transgenic crops had genes either for herbicide resistance or for insect resistance. In the United States the Coordinated Framework for Regulation of Biotechnology governs the regulation of transgenic organisms, including plants. The three agencies involved are: * USDA Animal and Plant Health Inspection Service – evaluates potential agricultural impacts such as gene flow and ‘weediness’ * EPA – evaluates potential environmental impacts, especially for genes which produce pesticides * DHHS Food and Drug Administration (FDA) – evaluates human health risk if the plant is intended for human consumption.
The potential impact on nearby ecosystems is one of the greatest concerns associated with transgenic plants. Transgenes have the potential for significant ecological impact if the plants can increase in frequency and persist in natural populations. This can occur: * if transgenic plants “escape” from cultivated to uncultivated areas. * if transgenic plants mate with similar wild plants, the transgene could be incorporated into the offspring. * if these new transgene plants become weedy or invasive, which could reduce biodiversity and might affect entire ecosystems. There are three possible avenues of hybridization leading to escape of a transgene: 1. Hybridization with non-transgenic crop plants of the same species and variety. 2. Hybridization with wild plants of the same species. 3. Hybridization with wild plants of closely related species, usually of the same genus. However, there are a number of factors which must be present for hybrids to be created. * The transgenic plants must be close enough to the wild species for the pollen to reach the wild plants. * The wild and transgenic plants must flower at the same time. * The wild and transgenic plants must be genetically compatible. * The hybrid offspring must be viable, and fertile. * The hybrid offspring must carry the transgene. Studies suggest that the most likely escape route for transgenic plants will be through hybridization with wild plants of related species. 1. It is known that some crop plants have been found to hybridize with wild counterparts. 2. It is understood, as a basic part of population genetics, that the spread of a transgene in a wild population will be directly related to the fitness effects of the gene in addition to the rate of influx of the gene to the population. Advantageous genes will spread rapidly, neutral genes will spread with genetic drift, and disadvantageous genes will only spread if there is a constant influx. 3. The ecological effects of transgenes are not known, but it is generally accepted that only genes which improve fitness in relation to abiotic factors would give hybrid plants sufficient advantages to become weedy or invasive. Abiotic factors are parts of the ecosystem which are not alive, such as climate, salt and mineral content, and temperature.