Botany

An Overview of the Soil Bacterium Agrobacterium Tumefaciens



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Agrobacterium tumefaciens (A. tumefaciens) is a widespread soil bacterium that causes a disease in plants called Crown Gall. This disease attacks plants such as fruit-bearing trees. A. tumefaciens is a unique in that it is "the only example of interkingdom DNA transfer." Because of its ability to transfer DNA directly to plants, it has a potentially important role in plant genetic engineering. It also causes one of the most common plant tumors and is widely studied to better understand its "cancer-causing" properties. The website not surprisingly labeled "Agrobacterium tumefaciens" (http://arabidopsis.info/students/agrobacterium/mechanism.html) provides an overview of this unique bacteria and its method of DNA transfer. T-DNA is a nucleoprotein complex-a nucleotide strand coated by a protein called VirE2. VirE2 assists and protects the DNA during intracellular transfer.

T-DNA initially exists as part of a plasmid vector in A. tumefaciens. The transfer mechanism is activated when a plant is injured at the root or stem. Chemicals released by the injured plant tissues provide a signal for A. tumefaciens to release the T-DNA. (These are probably the same signals that the plant uses to activate the healing process.) The signal is recognized through a two-step signal process. One protein called VirA acts as a sensor, and another protein-VirG-regulates cytoplasm response.

The post-recognition transfer process begins with splicing the T-DNA out of the plasmid vector by a restriction endonulcease. Once the T-DNA vector is "active", A. tumefaciens infects a plant by direct transfer of DNA (T-DNA for Transfer DNA). The T-DNA is excreted by A. tumefaciens and is then taken up by a plant. A. Tumefaciens must be attached to the injured plant) for the transfer process to occur. Once inside a plant cell, the T-DNA is incorporated into the plant cell's DNA. At this point, the cell is transformed into a cancerous cell. This results in the growth of a tumor on the plant.

A. tumefaciens is seen as a good potential candidate for plant genetic engineering because it has a high rate of success in gene transfer. It also is not like transposons in that it could affect functions related to transport and integration of genetic engineering.

Whether A. tumefaciens will have widespread use depends on many factors. One factor is the successful adoption of A. tumefaciens for a specific plant and delivery of a specific DNA vector. The A. tumefaciens DNA delivery mechanism has to be tailored to work with different plants. Another factor is alternative forms of DNA transfer. There are different processes such as "shooting" DNA into protoplast plant cells that are then grow into plants. Even if a success model is found for using A. tumefaciens in the development of a genetically engineered plant, there could be issues related to the scale-up and long-term production. Finally, there are environmental issues related to the use of a bacteria that is robust and is known for it cancer-causing capabilities.

Reference:
1. Agrobacterium tumefaciens (http://arabidopsis.info/students/agrobacterium/index.html)

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