Genetic Transformation of Plants by Agrobacterium
Agrobacterium tumefaciens causes crown gall disease in plants. Crown galls are cancerous growths composed of disorganized proliferating plant cells, often found near soil level at the junction of plant stem and root. Agrobacterium is an oncogenic agent which genetically transforms plant cells and directs the resulting tumours to synthesize special nutrients that support growth of the bacteria. A competitive advantage is conferred upon the inciting Agrobacterium strain because only it, or a related strain, can utilize the nutrients produced by the tumour as an energy source. The transformation process involves transfer of genetic information from the bacteria to the plant stimulated by compounds exuded from wounded plant cells. This is the only known example of inter-kingdom exchange of genetic material and has been described as ‘genetic colonization’ (Schell et al., 1979).
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