Preliminary Characterization of the hrp Gene Cluster of Pseudomonas syringae pv. pisi.

Hybridisation analysis, using DNA probes of the Pseudomonas syringae pv. phaseolicola (Pph) race 4 hrp cluster, detected a homologous cosmid clone from a genomic library of P. syringae pv. pisi (Ppi) race 4. The Ppi cosmid, pAV397, contains an insert of ca.15 kb DNA. A restriction endonuciease map of the insert was compared with the Pph main hrp cluster. The internal region of the hrpL gene, encoding an alternate sigma factor and known to be present on pPPY430, was shown by PCR analysis to be present on Ppi cosmid pAV397. Complementation of a Ppi race 4-like Hrp- mutant strain PT17 with either pAV397 or pPPY430, restored pathogenicity toward pea cultivar Kelvedon Wonder and the ability to elicit a hypersensitive reaction (HR) in pea cultivar Hursts Greenshaft and the non-host tobacco.