The T-DNA region genes are responsible for the tumorigenic process. Some of them control the production of plant growth hormones that cause proliferation of the transformed plant cells. The T-DNA region is flanked at both ends by 24 base pairs (bp) direct repeat border sequence called T-DNA borders. The T-DNA left border is not essential, but the right border is indispensable for T-DNA transfer. Ti plasmid is grouped into two general categories:

i) Nopaline type pTi

ii) Octopine type pTi

Both types of plasmid are shown in Figure 26.1 A, B.

Figure 26.1: the Ti plasmid: (A) nopaline type pTi; (B) Octopine type pTi