Agrobacterium Essay

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Agrobacterium tumefaciens is a pathogenic soil bacterium that causes a serious plant disease known as Crown gall. It is attracted to certain phytohormons (acetosyringone), produced when plant cells are wounded. Agrobacterium causes this disease by inserting a piece of DNA into the plant’s nuclear genome. The inserted DNA contains genes coding for enzymes required for the synthesis of unusual amino acids called opines as well as genes that result in aberrant production of plant hormones. Insertion of the DNA into the plant genome thus causes the disruption of normal cell growth resulting in the formation of large unorganized tumours which produce the opines. The bacteria can then grow on the tumours, using the opines as a food source. The transferred DNA, or T-DNA, is part of a large tumour-inducing (Ti) plasmid. The T-DNA carries an onc (oncogenic) region, which, by coding for the production of plant growth hormones, results in the proliferation of plant cells forming a tumour or gall. The T-DNA is bordered on each side by special DNA sequences called the T-DNA borders. Any DNA that is present between these borders will be transferred to the plant and inserted into the nuclear genome. This feature allows plant scientists to utilize Agrobacterium tumefaciens as a valuable research tool. If the tumour-inducing genes are removed from the Ti plasmid and replaced with a gene(s) that we wish to put into a plant, the altered Agrobacterium can then be used as a vehicle for plant transformation. The virulence (vir) genes, which produce the proteins for T-DNA transfer, acts in trans, therefore the genes don’t have to be on the same plasmid as the T-DNA border repeats. Therefore the T- region and the vir genes could be separated onto two different replicons. When these replicons are were within the same Agrobacteruim cell, products of their vir genes could act in trans on the

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