Avirulence gene avrPphC from Pseudomonas syringae pv. phaseolicola 3121: a plasmid-borne homologue of avrC closely linked to an avrD allele

Abstract

Cosmid clone pPsp01 from race 1 Pseudomonas syringae pv. phaseolicola isolate 3121 conferred a unique pattern of soybean cultivar reactions when expressed in P. s. pv. glycinea R4. The avirulence phenotype was shown to result from the presence in clone pPsp01 of an avrD allele as well as an additional avirulence gene located approximately 5-kb upstream. The new gene, called avrPphC, shows high identity to and is phenotypically identical to avrC, previously cloned from P. s. pv. glycinea race 0. avrD and avrPphC occur on an approximately 120-kb indigenous plasmid in P. s. pv. phaseolicola 3121. Although commonly observed in Xanthomonas campestris, this is the first noted occurrence of multiple avirulence genes on a single plasmid in Pseudomonas syringae. Unlike avrD, however, avrPphC does not appear to occur widely in pathovars of Pseudomonas syringae.