Publication

Journal	MOLECULAR PLANT-MICROBE INTERACTIONS
Volume (Issue)	25(9)
Page(s)	1198 - 1208
Title of proceedings	MOLECULAR PLANT-MICROBE INTERACTIONS

Many strains of the phytopathogenic bacterium Pseudomonas syringae pv. syringae synthesize the virulence factor syringolin A, which irreversibly inactivates the eukaryotic proteasome. Syringolin A, a peptide derivative, is synthesized by a mixed non-ribosomal peptide/polyketide synthetase encoded by five clustered genes, sylA-sylE. Biosynthesis of syringolin A, previously shown to be dependent on the gacA/gacS two component system, occurs in planta, and in vitro, but only under still culture conditions in a defined medium. Here we show that the sylC, sylD, and sylE genes of Pss B301D-R form an operon transcribed by promoter sequences located between the sylCDE operon and the sylB gene residing on opposite strands. Assays of overlapping sylB and sylCDE promoter deletions translationally fused to the lacZ gene defined promoter sequences required for gene activity both in vitro and in planta. Activation of both promoters depended on the sylA gene encoding an HTH LuxR-type transcription factor which was shown to directly bind to the promoters. Activity of the sylA gene in turn required a functional salA gene, which also encodes an HTH LuxR-type transcription factor. Furthermore, evidence is presented that acyl-homoserine lactone-mediated quorum sensing regulation is not involved in syringolin A biosynthesis, but that oxygen concentration appears to play a role.