Characterization of avrPphE, a Gene for Cultivar-Specific Avirulence from Pseudomonas syringae pv. phaseolicola Which Is Physically Linked to hrpY, a New hrp Gene Identified in the Halo-Blight Bacterium. John Mansfield. Biological Sciences Department, Wye College, University of London, Ashford, Kent, TN25 5AH, U.K. Carol Jenner, Ruth Hockenhull, Mark A. Bennett and Ruth Stewart. Biological Sciences Department, Wye College, University of London, Ashford, Kent, TN25 5AH, U.K. MPMI 7:726-739. Accepted 25 July 1995. Copyright 1994 The American Phytopathological Society.

The avirulence gene matching the R2 gene for resistance to halo-blight disease in Phaselous was cloned and se-quenced from race 4 strain 1302A of Pseudomonas syringae pv. phaseolicola. The predicted 41-kDa AvrPphE protein is hydrophilic, has no features that indicate function, and no similarity to other protein sequences. The promoter region of avrPphE contains a "harp box" motif. The gene was expressed more strongly in minimal than in nutrient-rich media. Lower concentrations of the phytoa-lexin phaseollin accumulated in tissue undergoing the hypersensitive reaction (HR) determined by avrPphE than by avrPphB. Homologs of avrPphE were detected in strains representing eight races of P. s. pv. phaseolicola including those virulent on cultivars with the R2 resistance gene, and in P. s. pv. (abaci but not in P. cichorii or P. s. pvs. coronafaciens, glycinea, maculicola, pisi, or syringae. Disruption of avrPphE prevented induction of the HR but did not appear to affect basic pathogenicity. Transposon mutagenesis and DNA sequencing showed that avrPphE was linked to hrpY a hrp locus identified at the left end of the hrp gene cluster. Sequence analysis showed that the region linked to avrPphE was very similar to DNA containing hrp genes from P. s. pv. syringae including hrpJ, hrpL, and hrpK.