Agrobacterium rhizogenes is a gram negative soil bacterium.^[25] It incites hairy root disease of many dicotyledonous plants. Its ability of A. rhizogenes to incite hairy root disease is determined by a virulence plasmid known as the Ri-plasmid  it contains a distinct segment (s) of DNA which is transferred to plant genome during infection.

Ri –plasmid 

Large plasmids were shown to be present in strains of A. rhizogenes. These strains are known to produce at least two classes of opines. One such class is represented by opines of agropine group, and agrocinopine group.^[25]

The strains which produce ally the agropine-type opines are known as the agropine-type strains, whereas the strains which produce all agropine-type opines excluding agropine are known as the mannopine-type strains.^[25]

Two T-DNA regions have been identified in agropine Ri-plasmids.^[25]

The two tDNAs are separated from each other by about 15 Kb of non-transferred DNA. The right T–DNA (TR) contains genes homologous to the T–DNA from Ti– plasmids. Most important among these are the genes homologous to the tms1 and tms2 of the Ti–plasmid.^[25]

Mutagenesis of this region in the Ri–plasmid is shown to result in the loss or attenuation of virulence. ^[25]

Image source : Figure 1, Vilas P. Sinkar, Frank F. White*, and Milton P. Gordon, Molecular biology of Ri-plasmid—A review, J. Biosci., Vol. 11, Numbers 1–4, March 1987 

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  Reference:

• Vilas P. Sinkar, Frank F. White*, and Milton P. Gordon, Molecular biology of Ri-plasmid—A review, J. Biosci., Vol. 11, Numbers 1–4, March 1987, pp. 47–57.