The model of agrobacterial transformation of a plant cell

Agrobacterium tumefaciens is a plant parasitic bacterium, possessing cytoplasmic tumour-inducing plasmid (Ti plasmid, or pTi) which contains the T-DNA (“transfer DNA”), enabled to penetrate a plant cell and incorporate into the plant genome, and also vir genes responsible for the entire process of transformation.

T-DNA encodes genes for the production of specialized amino acids (opines), which the bacteria can metabolize, and phytohormones, stimulating cell proliferation and gall formation.

Bacterial cell surface receptors detect signals of the degraded plant cell wall, and as a result the activation of vir genes takes place. Their products mediate replication and T-DNA transportation into the bacterium cell.

Agrobacterial transformation is extensively used in genetic engineering, but today binary vectors systems grow more and more popular. The latter include a plasmid, carrying T-DNA, where genes encoding opines and phytohormones have been replaced by a target transgene, and a separate helper plasmid on which only vir genes are arranged.

The model of binary vector system is not represented in this simplified illustration.