Highly conserved sequences flank avirulence genes: isolation of novel avirulence genes from Pseudomonas syringae pv. pisi.
DNA sequences flanking two avr genes (avrPpiA1 and avrPpiB1) from Pseudomonas syringae pv. pisi show a high degree of similarity. Specific primers designed from the conserved regions were used in PCR amplifications with all P. syringae pv. pisi races. As well as amplifying the expected avrPpiA- and avrPpiB-containing fragments, two additional fragments were amplified: one contained a single open reading frame (ORF1) and was found in races of genomic group II (2, 3A, 4A and 6); the second fragment contained two open reading frames (ORF2 and ORF3), separated by 658 nt, and was detected in all races. All three ORFs had G+C ratios (46.9-48 mol%) that were significantly less than that for P. syringae and each was preceded by a potential hrp box promoter. In P. syringae pv. phaseolicola, ORF1 and ORF2 each elicited a strong non-host hypersensitive reaction on bean leaves; ORF1 was designated avrPpiG, the product of which had strong similarity to AvrRxv, AvrBsT and YopP. ORF2 was identical to a gene, designated avrPpiC, previously isolated from P. syringae pv. pisi race 5. ORF3 was always found in association with avrPpiC and both were detected in a wide range of P. syringae pathovars. In contrast, avrPpiG was only detected in strains of P. syringae pv. pisi genomic group II and P. syringae pv. coronafaciens (ICMP 3113). In P. syringae pv. pisi, avrPpiG was plasmid-borne and avrPpiC and ORF3 were chromosomal. This conservation of flanking sequences has implications for the horizontal transfer of avirulence and virulence genes, suggesting that specific regions of the bacterial genome act as sites for their integration/excision.
Arnold
Dawn L
DL
Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK1.
Jackson
Robert W
RW
Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK1.
Fillingham
A Jane
AJ
Department of Biological Sciences, Imperial College, Wye, Ashford, Kent TN25 5AH, UK2.
Goss
Susan C
SC
Department of Biological Sciences, Imperial College, Wye, Ashford, Kent TN25 5AH, UK2.
Taylor
John D
JD
Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK3.
Mansfield
John W
JW
Department of Biological Sciences, Imperial College, Wye, Ashford, Kent TN25 5AH, UK2.
Vivian
Alan
A
Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK1.
D001426:Bacterial Proteins / Q000235:genetics*; D017124:Conserved Sequence; D003546:Cysteine Endopeptidases; D004269:DNA, Bacterial / Q000032:analysis; D007887:Fabaceae / Q000382:microbiology*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D010946:Plants, Medicinal; D016133:Polymerase Chain Reaction; D011549:Pseudomonas / Q000235:genetics* / Q000472:pathogenicity; D017422:Sequence Analysis, DNA; D020079:Terminal Repeat Sequences; D014774:Virulence
C096614:AvrPpiB1.R3 protein, Pseudomonas syringae; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D003546:Cysteine Endopeptidases