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

The avirulence gene matching the R2 gene for resistance to halo-blight disease in Phaselous was cloned and sequenced from race 4 strain 1302 A of Pseudomonas syringae pv, phaseolicola. The predicted 41-kDa AvrPp hE protein is hydrophilic, has no features that indicate function, and no similarity to other protein sequences. The promoter region of avrP phE contains a ''harp box'' motif. The gene was expressed more strongl y in minimal than in nutrient-rich media. Lower concentrations of the phytoalexin phaseollin accumulated in tissue undergoing the hypersensi tive 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 resist ance gene, and in P. s. pv. tabaci but not in P. cichorii or P. s. pvs . coronafaciens, glycinea, maculicola, pisi, or syringae. Disruption o f avrPphE prevented induction of the HR but did not appear to affect b asic pathogenicity. Transposon mutagenesis and DNA sequencing showed t hat avrPphE was linked to hrpY a hrp locus identified at the left end of the hrp gene cluster. Sequence analysis showed that the region link ed to avrPphE was very similar to DNA containing hrp genes from P. s. pv. syringae including hrpJ, hrpL, and hrpK.