ANALYSIS OF THE SYRP GENE, WHICH REGULATES SYRINGOMYCIN SYNTHESIS BY PSEUDOMONAS-SYRINGAE PV SYRINGAE

Syringomycin is a lipodepsinonapeptide phytotoxin synthesized hy Pseud omonas syringae pv. syringae on multienzymatic peptide synthetases. Se quence analysis of the interval between the syrB and syrD genes of P. syringae pv, syringae strain B301D revealed a 1,059-bp open reading fr ame (ORF), designated syrP. The predicted product of this ORF was a 39 .6-kDa protein consisting of 353 amino acid residues. Searches of prot ein sequence databases demonstrated that SyrP was most similar to hist idine kinases such as the CheA regulatory protein of Escherichia coli. The predicted SyrP sequence was aligned with the N terminus of CheA, a region corresponding to the phosphotransfer and acceptor domains of CheA, The SyrP region that aligns with the phosphotransfer domain of C heA contained a His at position 101 which is flanked by a weak consens us sequence of the unorthodox sensory kinase subfamily of two-componen t regulatory systems, Strain B301D-31, obtained by site-directed inser tional mutagenesis of the syrP gene, exhibited an unusual pleiotropic phenotype including a failure to produce syringomycin in liquid media in contrast to production of elevated levels of the toxin on agar medi a. The syrP mutant was relieved of the suppression of toxin production that accompanies inorganic phosphate concentrations of > 1 mM on agar media. Nevertheless, the syrP mutant was substantially less virulent than the wild-type strain in pathogenicity assays in cherry fruits. Th ese results suggest that the syrP gene encodes a regulatory protein th at participates in a phosphorylation cascade controlling syringomycin production and virulence in P. syringae pv, syringae.