IDENTIFICATION OF A PATHOGENICITY LOCUS, RPFA, IN ERWINIA-CAROTOVORA SUBSP CAROTOVORA THAT ENCODES A 2-COMPONENT SENSOR-REGULATOR PROTEIN

A mutant of Erwinia carotovora subsp. carotovora, AH2552, created by a Mud1 insertion was found to be reduced in plant pathogenicity and def icient in extracellular protease and cellulase activity, although it p roduced normal levels of pectate lyase and polygalacturonase. A cosmid clone, pEC462, was isolated from a wild-type E. carotovora subsp, car otovora DNA library that concomitantly restored pathogenicity and prot ease and cellulase activities of AH2552 to wild-type levels when prese nt in trans. The genetic locus that was disrupted in AH2552 by inserti on of Mud1 has been designated rpfA, for regulator of pathogenicity fa ctors. Sequencing of the rpfA region identified an open reading frame of 2,787 bp, and the predicted 929-amino acid polypeptide shared high identity with several two-component sensor-regulator proteins: BarA fr om Escherichia coli, ApdA from Pseudomonas fluorescens, PheN from P. t olaasii, RepA from P. viridiflava, LemA from P. syringae pv. syringae, and RpfC from Xanthomonas campestris pv. campestris. The RpfA locus d escribed in this study encodes a putative sensor kinase protein that i s involved in both extracellular protease and cellulase production and the pathogenicity of E. carotovora subsp. carotovora on potato tubers .