- The Ti plasmid, or tumor-inducing plasmid, is an extrachromosomal DNA molecule found naturally in Agrobacterium tumefaciens. This bacterium is infamous for causing crown gall disease in plants, characterized by tumor-like growths.
- The Ti plasmid plays a central role in this process, as it contains a segment called T-DNA that is transferred into the genome of plant cells. Once integrated, the T-DNA region manipulates the plant’s hormone production, triggering uncontrolled cell division that results in tumor formation. Additionally, it promotes the synthesis of opines—specialized compounds that serve as nutrients exclusively for Agrobacterium tumefaciens.
- Structurally, the Ti plasmid is divided into several functional regions. The T-DNA region is responsible for tumor formation and opine production, while the virulence (vir) genes are crucial for the transfer of T-DNA into the plant genome. These vir genes facilitate processes such as T-DNA excision, transportation across cell membranes, and integration into the plant’s DNA. The plasmid also contains genes for opine catabolism, which enable the bacterium to metabolize and derive energy from opines produced by infected plant cells. Finally, the replication and maintenance regions ensure the plasmid’s stability and propagation within the bacterial host.
- Due to its remarkable ability to transfer DNA across kingdoms, the Ti plasmid has become a powerful tool in molecular biology and plant genetic engineering. By modifying the T-DNA region, researchers can use the Ti plasmid to introduce desired genes into plants, creating transgenic plants for various applications, including improving crop traits and studying gene function. Its versatility continues to make it a cornerstone of plant biotechnology.
