Induction of Crown Gall Disease by the Ti plasmid

Agrobacterium is a bacterium that grows in association with plant roots. The bacterium carried a naturally-occuring plasmid, Ti, that contains a gene region called T-DNA. In crown gall disease, the T-DNA region is randomly integrated into the host plant chromosomal DNA: this causes the formation of tumor-like growths at the base of the plant. The Ti plasmid thus behaves like a natural vector, and can be used to genetically engineer plants.