GM techniques turn a plant parasite into a potential saviour of rice producers
Date: 17.8.2006
Beautiful and much loved shrubs and trees afflicted with the disease produce swellings, or galls, along the length of the branches and roots and often die. New plants grown in the old soil almost always suffer the same fate.
I wait for Lindsay, a professional gardener, to have a consoling cup of tea before telling her that scientists have been getting pretty excited about the bacterium responsible for this pesky disease.
The bacterium in question is Agrobacterium tumefaciens. It usually lives a fairly innocent existence in the soil surrounding the root, surviving on excess nutrients that naturally leak from the plant. However, a more ingenious and sinister side to its personality is revealed if a root is damaged or broken.
The bacterium is able to detect the presence of a wound thanks to abnormally high levels of plant nutrients flooding out into the surrounding soil, and loses no time in leaping into action.
The bacterium has a separate piece of genetic material, in the form of circular DNA, which provides it with all the tools it needs to invade the plant. Once the bacterium is inside, a section of this circular DNA, called transfer-DNA (T-DNA) is snipped out. The T-DNA then invades a plant cell, where it is incorporated into the genome, and causes the plant cell to produce the proteins coded for by the bacterial T-DNA. Infected cells grow unusually large and replicate rapidly, causing the galls on the plant that so horrify gardeners. This neat trick also causes the cells in the galls to act as food factories, pumping out nutrients for the bacteria to feast on.
This is the part that so excites scientists. Transfer of DNA between organisms of different kingdoms is exceptionally rare. When this infection mechanism was discovered, the immediate thought was that if it is possible for T-DNA from the bacterium to work its way into the plant's genetic material, then perhaps this process could be used as a vehicle for other foreign genes. This has now been achieved; by inserting a gene of interest into the Agrobacterium T-DNA, it possible to instruct plant cells to produce the protein coded for by the gene. Plants modified in this way are known as transgenic plants, which have a myriad of potential uses.
Enamul Hoque, a postgraduate working for Prof John Mansfield at Imperial College London, is modifying cultivars of rice found in Bangladesh using Agrobacterium. "The main objective is increased food production, and development of salt tolerance. Bangladesh is particularly prone to seawater flooding, and it is a huge problem," says Prof Mansfield.
The production of transgenic - genetically altered - rice cultivars in the lab has been successful, but, as Prof Mansfield points out, the transfer from lab to field is a complex process.
"The first thing is to educate the people living in the area that genetically modified crops, if used appropriately, are safe," he says. "At the moment, production is industry-led and the main aim is profit; what we need is an approach that is going to improve the situation of smallholders."
The hope is that the successful generation of salt-tolerant rice varieties will reassure local farmers that genetic modification is a tool that can be used to their direct benefit. To this end, a large proportion of the transgenic plant technologies now being pioneered are focused on providing benefit for the communities in which they are used.
An example is the development of "edible vaccines" - food crops such as lettuce that are modified by Agrobacterium to carry an antigen from pathogens such as hepatitis B virus, thus providing a cheap means of vaccination in less economically developed countries.
Lindsay seems consoled by this alter ego of the bug. In the future it is hoped that the potential benefits of Agrobacterium-transformed plants can be taken from lab to field in a professional and safe manner. It is then that we can hope to see Agrobacterium as a tool capable of helping to remedy worldwide problems of famine and disease with a novelty matched only by that of its biology.
Leili Farzenah, 19, studies the use of viruses - retroviruses - for genetic engineering at Imperial College London. On being told she had won the younger category, she said: "I don't know what to say. Thank you. I can't thank you enough."
"Source":[ http://www.checkbiotech.org/root/index.cfm?fuseaction=news&doc_id=13271&start=1&control=170&page_start=1&page_nr=101&pg=1]
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