AVIRULENCE GENE-D OF PSEUDOMONAS-SYRINGAE PV. TOMATO MAY HAVE UNDERGONE HORIZONTAL GENE-TRANSFER

Avirulence gene D (avrD) is carried on the B-plasmid of the plant path ogen Pseudomonas syringae pv. tomato with plasmid-borne avrD homologs widely distributed among the Pseudomonads. We now report sequences in the soft rot pathogen Erwinia carotovora that cross-hybridize to avrD suggesting a conserved function beyond avirulence. Alternatively, avrD may have been transferred horizontally among species: (i) DNA linked to avrD shows evidence of class II transpositions and contains a novel IS3-related insertion sequence, and (ii) short sequences linked to av rD are similar to pathogenicity genes from a variety of unrelated path ogens. We have also identified the gene cluster that controls B-plasmi d stability. (C) 1997 Federation of European Biochemical Societies.