Ti-Plasmid - The Ti plasmid is a large conjugative plasmid or megaplasmid of about 200 kb (range 150-250 kb). The pTi and pRi are unique bacterial plasmids in the following two respects.

(1) They contain some genes, located within their T-DNA, which have regulatory sequences recognised by plant cells, while their remaining genes have prokaryotic regulatory sequences.
(2) These plasmids naturally transfer a part of their DNA, the T-DNA, into the host plant genome, which makes Agrobacterium a natural genetic engineer.

The Ti plasmids are classified into different types based on the type of opine, namely, octopine, nopaline, succinamopine and leucinopine, produced by their genes.