Location and activity of members of a family of virPphA homologues in pathovars of Pseudomonas syringae and P. savastanoi

Abstract

Summary virPphA is a major determinant of the pathogenicity of Pseudomonas savastanoi pv. phaseolicola to Phaseolus bean. A family of homologues of virPphA was detected in pathovars of P . savastanoi and P . syringae . We examined the structure and activity of alleles designated virPphA , virPphA Pgy , and virPphA Psv from P . savastanoi pathovars phaseolicola , glycinea , and savastanoi , respectively, and avrPtoB from P . syringae pv. tomato . Sequencing showed that the virPphA Pgy homologue had a 48‐bp central deletion in the open reading frame (ORF) compared with virPphA and virPphA Psv , but otherwise all three P . savastanoi alleles had > 98% identity at the DNA level. By contrast, AvrPtoB from P . syringae pv. tomato strain DC3000 was predicted to have only 51% amino acid similarity with VirPphA. All ORFs have an upstream hrp ‐box promoter indicating potential regulation by HrpL. Each cloned homologue was introduced into the P. savastanoi pv. phaseolicola strain RW60, which lacks a native plasmid carrying virPphA as part of a pathogenicity island (PAI), and which is not pathogenic on bean. The homologues all restored virulence, as measured by the development of water‐soaked lesions in bean pods, and increased bacterial populations in leaves compared with RW60 alone. RW60 harbouring virPphA or virPphA Psv elicited a strong hypersensitive reaction (HR) in soybean cv. Osumi; the presence of avrPtoB caused a weak HR, but virPphA Pgy did not affect the null reaction observed in soybean with RW60 alone. A second effector gene, avrPphD , was detected on the genomic clones carrying virPphA Pgy and virPphA Psv . avrPphD was also present in both P . savastanoi pv. phaseolicola and P . syringae pv. tomato , but elsewhere in their genomes. Comparison of the genomic locations of virPphA and other effectors found in the P. savastanoi pv. phaseolicola PAI revealed the greatest divergence of the sequences surrounding virPphA to be in ...

Natural Variation in the Pto Disease Resistance Gene Within Species of Wild Tomato (Lycopersicon). II. Population Genetics of Pto

“…pv. phaseolicola, it can restore water-soaking ability to this pathogen ( Jackson et al 2002). Recently, the phenotype of a double-mutant Pst strain, lacking both AvrPto and AvrPtoB, was generated (Lin and Martin 2005).…”

Pseudomonas syringae pv. phaseolicola can be separated into two genetic lineages distinguished by the possession of the phaseolotoxin biosynthetic cluster

“…phaseolicola strain 1449B spans around 30 kb of contiguous DNA located in the 150 kb native plasmid and includes several effector genes, some of which are involved in pathogenicity and virulence (Jackson et al, 1999;Tsiamis et al, 2000). Other pathovars of P. syringae contain homologues of one or more of the genes included in this PAI, although the PAI itself is not conserved among them and the number of genes and their physical location (plasmid versus chromosome) is highly variable (Jackson et al, 2002). However, the PAI would appear to be conserved among the Pph1 group of strains since all of them contained a large plasmid that hybridized to both avrD-and avrPphC-specific probes.…”

Global Genomic Analysis of Pseudomonas savastanoi pv. savastanoi Plasmids

“…savastanoi is unknown except for hopAB1 (formerly virPphA) and avrB2 (formerly avrPphC) genes, previously identified on plasmids isolated from two different P. savastanoi pv. savastanoi strains (21). Widely distributed among P. syringae and P. savastanoi strains (23), hopAB1 was the most common effector gene detected among the P. savastanoi pv.…”

“…strain (9). On the other hand, other IS elements, such as IS52 and IS801, have been connected to the transfer of iaa genes between A. tumefaciens and P. savastanoi (45) or to movement of virulence effectors (avrA and avrB2) (21) in P. savastanoi.…”