- T-DNA
T-DNA is the transferred
DNA of the tumor-inducing (Ti) plasmid of some species of bacteria such as "Agrobacterium tumefaciens " and "Agrobacterium rhizogenes ". It derives its name from the fact that the bacterium transfers this DNA fragment into the host plant's nuclear DNAgenome . The T-DNA is bordered by 25-base-pair repeats on each end. Transfer is initiated at the left border and terminated at the right border and requires the "vir" genes of the Ti plasmid.The bacterial T-DNA is about 20,000 base pairs long and contains
gene s that code forenzyme s synthesizingopines andphytohormone s. By transferring the T-DNA into the plant genome, the bacterium essentially reprograms the plant cells to grow into a tumor and produce a unique food source for the bacteria. The synthesis of the plant hormonesauxin andcytokinin enables the plant cell to grow uncontrollably, thus forming thecrown gall tumor s typically induced by "Agrobacterium" infection. The opines areamino acid derivatives used by the bacterium as a source of carbon and energy.T-DNA transformation
"Agrobacterium"-mediated T-DNA transfer is widely used as a tool in
biotechnology . Ingenetic engineering , the tumor-promoting and opine-synthesis genes are removed from the T-DNA and replaced with a gene of interest and/or a selection marker. "Agrobacterium" is then used as a vector to transfer the engineered T-DNA into the plant cells where it integrates into the plant genome. This method can be used to generatetransgenic plant s carrying a foreign gene.T-DNA mutagenesis
The same procedure of T-DNA transfer can be used to disrupt genes via
insertional mutagenesis . Not only does the inserted T-DNA sequence create a mutation but it also 'tags' the affected gene, thus allowing for its isolation. This method is used widely to study gene function in plants, such as the model plant "Arabidopsis thaliana ".References
*P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): "Biology of Plants", 7th Edition, W.H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2
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