The T-DNA, or transfer DNA, is a specific segment of DNA that originates from a tumor-inducing (Ti) plasmid within the Agrobacterium bacterium, notably Agrobacterium tumefaciens. This bacterial DNA has the unique ability to transfer itself into the nuclear genome of host plants.
Key Characteristics of T-DNA
- Source: T-DNA is derived from the Ti plasmid, a specialized plasmid found in Agrobacterium.
- Transfer: It is notable for its capacity to transfer from the bacterium into the host plant's nuclear DNA genome, causing genetic modification.
- Essential Regions: The capability of the Ti plasmid to transfer DNA is attributed to two essential regions required for this process.
- Border Sequences: T-DNA is flanked by 25-base-pair repeats at each end which are crucial for its recognition and transfer by the Agrobacterium machinery.
How T-DNA Transfer Works
| Step | Description |
|---|---|
| Bacterial Infection | Agrobacterium infects the plant cells, usually through a wound. |
| T-DNA Excision | The T-DNA region is excised from the Ti plasmid by Agrobacterium enzymes. |
| Transfer to Nucleus | The T-DNA, along with bacterial proteins, is transported into the nucleus of the host plant cell. |
| Integration | The T-DNA is integrated into the host plant's chromosomal DNA through a non-homologous recombination mechanism, thus becoming part of the plant’s genome. |
- Consequence: Once integrated, the T-DNA's genes are expressed in the host plant cells. These genes typically cause abnormal cell growth and can induce the formation of tumors (also called crown gall tumors).
T-DNA in Plant Biotechnology
The ability of T-DNA to transfer and integrate into plant genomes is harnessed in plant biotechnology. By removing the tumor-inducing genes and inserting genes of interest, scientists can use the T-DNA delivery system to genetically modify plants. This makes it an effective tool for producing transgenic crops with improved traits such as pest resistance and herbicide tolerance.
