A physical map of the syringomycin and syringopeptin gene clusters localized to an approximately 145-kb DNA region of Pseudomonas syringae pv. syringae strain B301D

Genetic and phenotypic mapping of an approximately 145-kb DraI fragment of Pseudomonas syringae pv. syringae strain B301D determined that the syringom ycin (syr) and syringopeptin (syp) gene clusters are localized to this frag ment. The syr and syp gene clusters encompass approximately 55 kb and appro ximately 80 kb, respectively. Both phytotoxins are synthesized by a thiotem plate mechanism of biosynthesis, requiring large multienzymatic proteins ca lled peptide synthetases. Genes encoding peptide synthetases were identifie d within the syr and syp gene clusters, accounting for 90% of the DraI frag ment. In addition, genes encoding regulatory and secretion proteins were lo calized to the DraI fragment. In particular, the salA gene, encoding a regu latory element responsible for syringomycin production and lesion formation in P. syringae pv. syringae strain B728a, was localized to the syr gene cl uster. A putative ATP-binding cassette (ABC) transporter homolog was determ ined to be physically located in the syp gene cluster, but phenotypically a ffects production of both phytotoxins. Preliminary size estimates of the sy r and syp gene clusters indicate that they represent two of the largest non ribosomal peptide synthetase gene clusters. Together, the syr and syp gene clusters encompass approximately 135 kb of DNA and may represent a genomic island in P. syringae pv. syringae that contributes to virulence in plant h osts.