INVOLVEMENT OF A PLASMID IN THE HAIRY ROOT DISEASE OF PLANTS CAUSED BY AGROBACTERIUM-RHIZOGENES

Agrobacterium rhizogenes causes a proliferation of roots on plants that it infects. This is in contrast to Agrobacterium tumefaciens which causes gall or tumor formation on its hosts. A large molecular weight plasmid (1.1 × 108) in A. rhizogenes strain A4 is correlated with the infectivity of this organism. However, this plasmid apparently carries additional information not vital to the infection process. Experimental evidence supporting these conclusions is: (i) A. rhizogenes A4 loses infectivity when all or part of the plasmid is lost after treatment with ethidium bromide or after heating at 37 °C. (ii) There occurs successful conjugational transfer of the A4 plasmid in planta to a noninfectious, antibiotic-resistant A. radiobacter. Infectious transconjugants were antibiotic resistant and contain a plasmid comparable to that of A. rhizogenes A4. (iii) A. rhizogenes A4 and the transconjugants possessed identical EcoR1 restriction endonuclease patterns, whereas three ethidium bromide-treated isolates that were noninfectious but plasmid containing had lost or gained bands in the pattern. The infectious plasmid of A. rhizogenes A4 has been designated pHrA4. Some potential benefits of the A. rhizogenes plasmid to agriculture are discussed. © 1979.