1.2. Ri plasmid

Agrobacterium rhizogenes is a soil born gram negative bacterium. It causes hairy root disease of many dicotyledonous plants. The ability of A. rhizogenes to incite hairy root disease is confirmed by a virulence plasmid, which is similar to that found in Agrobacterium tumefaciens which causes Crown gall tumors of plants. The virulence plasmid of A. rhizogenes is commonly known as the Ri-plasmid (pRi). The pRi have extensive functional homology with the pTi. The pRi contains distinct segment(s) of DNA, which is transferred to plant genome during infection. The transfer T-DNA to the plant genome is mediated by another segment on the plasmid known as the virulence (vir) region. All strains of A. rhizogenes are known to produce agrocinopine.

Figure 26.2: Ri plasmid