Agrobacterium tumefaciens

• Agrobacterium tumefaciens is a pathogen (disease-causing microbe) that specifically infects several dicot plants.
• This bacterium has a unique ability to insert a specific piece of its own DNA directly into the host plant's DNA.
• This transferable piece of DNA is known as T-DNA.
• The T-DNA is naturally present inside a specific plasmid of this bacterium.
• This plasmid is popularly referred to as the Ti plasmid.

• When the bacterium infects the plant, the insertion of the T-DNA transforms the normal, healthy plant cell into a tumour cell.
• Once transformed, the T-DNA directs these tumour cells to continuously produce specific chemicals that are required by the pathogen to survive.

The Ti plasmid consists of several important regions:

1. T-DNA Region: This is the section bounded by a "right border" and a "left border". It contains specific genes responsible for:

• Auxin synthesis.
• Cytokinin synthesis.
• Opine synthesis.

2. Virulence Genes: Required to help transfer the T-DNA into the plant cell.

3. Ori: The origin of replication, which allows the plasmid to multiply.

4. Opine Utilisation Region: Allows the bacterium to use the opines produced by the plant tumour.

Plasmid of Agrobacterium tumefaciens

• Agrobacterium tumefaciens is a bacterial pathogen that specifically infects several types of dicot plants.
• The bacterium possesses a specialised plasmid, widely known as the Ti plasmid, which contains a transferable DNA segment called T-DNA.
• During an infection, the pathogen successfully inserts a piece of this T-DNA directly into the DNA of the host plant.
• This genetic insertion alters normal cellular functions, transforming healthy plant cells into tumour cells.
• Consequently, the inserted T-DNA directs these newly formed tumour cells to synthesise and produce specific chemicals required by the pathogen.