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

Abstract

The bean (Phaseolus spp.) plant pathogen Pseudomonas syringae pv. phaseolicola is characterized by the ability to produce phaseolotoxin (Tox + ). We recently reported that the majority of the Spanish P. syringae pv. phaseolicola population is unable to synthesize this toxin (Tox " ). These Tox " isolates appear to lack the entire DNA region for the biosynthesis of phaseolotoxin (argK-tox gene cluster), as shown by PCR amplification and DNA hybridization using DNA sequences specific for separated genes of this cluster. Tox + and Tox " isolates also showed genomic divergence that included differences in ERIC-PCR and arbitrarily primed-PCR profiles. Tox + isolates showed distinct patterns of IS801 genomic insertions and contained a chromosomal IS801 insertion that was absent from Tox " isolates. Using a heteroduplex mobility assay, sequence differences were observed only among the intergenic transcribed spacer of the five rDNA operons of the Tox " isolates. The techniques used allowed the unequivocal differentiation of isolates of P. syringae pv. phaseolicola from the closely related soybean (Glycine max) pathogen, P. syringae pv. glycinea. Finally, a pathogenicity island that is essential for the pathogenicity of P. syringae pv. phaseolicola on beans appears to be conserved among Tox + , but not among Tox " isolates, which also lacked the characteristic large plasmid that carries this pathogenicity island. It is proposed that the results presented here justify the separation of the Tox + and Tox " P. syringae pv. phaseolicola isolates into two distinct genetic lineages, designated Pph1 and Pph2, respectively, that show relevant genomic differences that include the pathogenicity gene complement.

Regional variations in the population structure of Pseudomonas syringae pathovar phaseolicola from Spain are revealed by typing with PmeI pulsed-field gel electrophoresis, plasmid profiling and virulence gene complement

“…Nevertheless, it has been reported that the majority of the Spanish isolates of P. syringae pv. phaseolicola are unable to synthesize phaseolotoxin due to the absence of the entire argK-tox cluster (González et al, 2003;Oguiza et al, 2004;Rico et al, 2003). Genomic differences, including pathogenicity gene content and location, prompted the separation of toxigenic and non-toxigenic isolates into two distinct lineages, termed Pph1 and Pph2, respectively (Oguiza et al, 2004).…”

“…phaseolicola are unable to synthesize phaseolotoxin due to the absence of the entire argK-tox cluster (González et al, 2003;Oguiza et al, 2004;Rico et al, 2003). Genomic differences, including pathogenicity gene content and location, prompted the separation of toxigenic and non-toxigenic isolates into two distinct lineages, termed Pph1 and Pph2, respectively (Oguiza et al, 2004). These studies were performed with isolates from Castilla y Leó n (94 223 km 2 ), the largest dry bean producing region of Spain, where most of the crop is dedicated to common bean landraces of different varieties (riñó n, canela, pinta, morada, palmeña, etc.).…”

Short communication. Detection by multiplex PCR and characterization of nontoxigenic strains of Pseudomonas syringae pv. phaseolicola from different places in Spain

“…Incidentally, all the P. syringae pv. phaseolicola tox-strains analyzed so far also lacked other genes of the phaseolotoxin biosynthesis cluster and failed to produce phaseolotoxin (Rico et al, 2003;Oguiza et al, 2004). Additionally, the tox-isolates also failed to react with one of the few commercial antibodies for the serological detection of P. syringae pv.…”

“…However, it was recently showed that more than 66% of the P. syringae pv. phaseolicola isolates causing field epidemics in Castilla y León, Spain, were nontoxigenic and did not contain DNA specific for the biosynthesis of phaseolotoxin (Rico et al, 2003;Oguiza et al, 2004). The strains of P. syringae pv.…”

“…The primers used in the multiplex PCR were primer pair P5.1-P3.1 (Schaad et al, 1995;Zhang and Patil, 1997), specific of open reading frame (ORF) 6 from locus phtE of the phaseolotoxin biosynthesis cluster, and primer pair P3004L and P3004R, which amplify a 0.24 kb fragment (GenBank acc no. AJ568001) that has been observed only in nontoxigenic strains (Oguiza et al, 2004). Additionally, 100 µl aliquots of a 1/10 dilution of the concentrated seed soakate were cultured on MT plates for 24-48 h at 28ºC, and putative colonies belonging to P. syringae pvs.…”