AVIRULENCE GENE AVRPPIA FROM PSEUDOMONAS-SYRINGAE PV PISI IS NOT REQUIRED FOR FULL VIRULENCE ON PEA

The open reading frame encoding the avirulence gene acrPpiA1, previous ly cloned from race 2 of Pseudomonas syringae pv. pisi, has been subcl oned and shown to express peptides corresponding to all six possible s tart codons. The half-life of the peptides was found to be approximate ly 5 min in Escherichia coli. Transposon insertions which inactivate t he gene in P. syringae pv. Pisi were located both within the open read ing frame and in the upstream regulatory sequence, the hrp-box. Homolo gues of the gene were present only in races 5 and 7, which expressed t he avirulence phenotype. The gene was present on the chromosome in all race 2 isolates tested, but was plasmid-borne in the type strains of races 5 and 7. In contrast to the homologue avrRpm1 cloned from P. syr ingae pv. maculicola, marker-exchange mutagenesis of the gene in races 2 and 7 of P. syringae pv. pisi was not found to affect pathogenicity towards the susceptible host as indicated by symptom development or b acterial growth in the plant. (C) 1997 Academic Press Limited.