Back to IndexTransgenic methods have now been developed for a number of important crop plants such as rice, cotton, soybean, oilseed rape and a variety of vegetable crops like tomato, potato, cabbage and lettuce. New plant varieties have been produced using bacterial or viral genes that confer tolerance to insect or disease pests and allow plants to tolerate herbicides, making the herbicide more selective in its action against weeds and allowing farmers to use less herbicide.
A new variety of cotton, for example, has been developed that uses a gene from the bacterium Bacillus thuringiensis to produce a protein that is specifically toxic to certain insect pests including bollworm, but not to animals or humans. (This protein has been used as a pesticide spray for many years.) These transgenic plants should help reduce the use of chemical pesticides in cotton production, as well as in the production of many other crops which could be engineered to contain the Bacillus thuringiens is gene. In another case, a gene from the potato leaf-roll virus has been introduced into a potato plant, giving the plant resistance to this serious potato disease, which is particularly prevalent in Queensland.
Transgenic technologies are now being used to modify other important characteristics of plants such as the nutritional value of pasture crops or the oil quality of oilseed plants like linseed or sunflower.
Eventually it may also be possible to develop crops for non-food uses by modifying the starches and oils they produce to make them more suitable for industrial purposes, or to use plants rather than animals to make antibodies for medical and agricultural diagnostic purposes. In the cut flower industry, transgenic research may yield products such as blue carnations as a novelty items.
Although the basic coding system is the same in all organisms, the fine details of gene control often differ. A gene from a bacterium, say, will often not work correctly if it is introduced unmodified into a plant or animal cell. The genetic engineer must first construct a transgene - the gene to be introduced; this is a segment of DNA containing the gene of interest and some extra material that correctly controls the gene's function in its new organism. The transgene must then be inserted into the second organism.
Making a transgene: All genes are controlled by a special segment of DNA found on the chromosome next to the gene and called a promoter sequence. When making a transgene, scientists generally substitute the organism's own promoter sequence with a specially designed one that ensures that the gene will function in the correct tissues of the animal or plant and also allows them to turn the gene on or off as needed. For example, a promoter sequence that requires a dietary "trigger" substance can be used to turn on genes for important hormones in animals; the animal would not produce the new hormone unless fed the appropriate trigger.
Inserting the transgene in plants: Unlike animals, plants do not have a separate germline (eggs and sperm) and all cells of a plant retain the capacity to develop into a whole plant. This makes inserting the transgene much simpler. The transgene can be introduced into a single cell by a variety of physical or biological techniques, including using viruses or derivatives to carry the new gene into the plant cells.
Tissue culture techniques can then be used to propagate that cell and encourage its development into a transgenic plant, all of whose cells contain the transgene. Once the plant is produced, nature takes over and increases plant numbers by normal seed production.