Introduction
The study of transgenic or genetically modified plants is currently attracting significant interest because of its potential applications in industry, the environment, in the home and in medicine. Most genetic modification is perceived as being the insertion of foreign DNA into the genome of the target organism, and hence there is much debate as to whether this will have any unseen consequences in the future, and whether it is morally acceptable. There are also many problems associated with current methods of transgenic plant production, most notably the low transformation frequency encountered, or the failure of transgenic plants to grow at all. The use of Agrobacterium tumefaciens in transgenic plant production has arisen from the need to find an effective vector system to successfully integrate the gene of interest into the correct area of the plant genome.In recent years, the subject of uncontrolled cellular growth; Cancer, has been the focus of considerable attention as a result of its life threatening nature in humans. Extensive studies have unlocked information and provided a comprehensive knowledge base of undifferentaiated tissue growth in mammals, however little attention has been paid to cancer found in the plant kingdom. Agrobacterium tumefaciens causes one of the most common plant tumours, commonly known as Crown Gall disease which affects a wide variety of plants. Much research has taken place in an effort to understand the mechanism by which the bacterium infects the plant cell, in the hope that the bacterium can be used as a vector system to transfer foreign DNA into a plant genome with a higher degree of success than is currently seen with traditional methods.
Crown Gall disease is a common plant pathogen, affecting over 600 types of plants. Agrobacterium tumefaciens is a ubiquitous micro-organism that can be found in most soil samples. The disease mostly affects monocotyledonous species, such as woody and herbaceous plants and can be identified by the appearance of tumnours or galls of varying size and shape on the lower stem and main roots of the plant. Crown Gall disease can affect many commercially important and valuable crops such as Grapes, Rice and Sugar Beet.
Current Problems
Plant disease is currently a major problem facing the developed world. Currently as much as 30% of the yearly total production of food crops is lost due to plant disease. At the current time, there is enough food produced to feed the population, but only just. If the predicted population increase over the next 2-3 decades take place, it will be necessary to increase food production to meet demand. As such a large proportion of crops are lost to plant pathogens each year, there is currently much interest in developing strategies to increase plants natural resistance to pathogenic attack. A. tumefaciens can remain dormant in the soil over winter, and can live saprophytically for many years.
The diagram below gives some of the applications for plant transformation technology. Clicking the picture will open a larger image.
