THE FAS OPERON OF RHODOCOCCUS FASCIANS ENCODES NEW GENES REQUIRED FOREFFICIENT FASCIATION OF HOST PLANTS

Three virulence loci (fas, aft, and hgp) of Rhodococcus fascians D188 have been identified on a 200-kb conjugative linear plasmid (pFiD188). The fns locus was delimited to a 6.5-kb DNA fragment by insertion mut agenesis, single homologous disruptive recombination, and in trans com plementation of different avirulent insertion mutants. The locus is ar ranged as a large operon containing six open reading frames whose expr ession is specifically induced during the interaction with host plants . One predicted protein is homologous to P-450 cytochromes from actino mycetes. The putative ferredoxin component is of a novel type containi ng additional domains homologous to transketolases from chemoautotroph ic, photosynthetic, and methylotrophic microorganisms. Genetic analysi s revealed that fas encodes, in addition to the previously identified ipt, at least two new genes that are involved in fasciation developmen t, one of which is only required on older tobacco plants.