The Agrobacterium Rhizogenes Root-Inducing System

Abstract

In sensitive dicotyledoneous plants, Agrobacterium rhizogenes inoculation in wounds result first in the formation of a small callus that resembles the lesions induced in the same plant hosts by the related pathogen Agrobacterium tumefaciens. The fundamental difference between both pathogens is that in the former, a population of callus cells promptly differenciates in root-like tissue (hairy root), which accounts for most of the cell proliferation in advanced stages of the infection. The hairy-root tissue of many plants can be propagated in axenic medium for long periods. In these conditions, portions of the cultured hairy roots often differenciate in shoots, from which whole plants can be regenerated. Molecular biology studies show that the cultured hairy roots and the regenerated plants carry DNA sequences (T-DNA or transferred DNA) corresponding to an A. rhizogenes large plasmid (the Ri plasmid) in their genome (Chilton et al., 1982; White et al., 1982; Willmitzer et al., 1982).