Xanthomonas campestris pathovar campestris is the causal agent of black rot disease of cruciferous plants. A cell-cell signalling system encoded by genes within the rpf cluster is required for the full virulence of this plant pathogen. This system has recently been implicated in regulation of the formation and dispersal of Xanthomonas biofilms. (C) 2004 Elsevier SAS. All rights reserved.