In Pseudomonas syringae, the GacS/GacA two-component system regulates the production of the phytotoxins syringomycin and syringopeptin [18–20], tabtoxin [21, 22] and phaseolotoxin [23]. In P. syringae pv. tomato DC3000, GacS/GacA regulate the hrpR, hrpS, and hrpL genes, which are required for the activation of the Hrp type III secretion and

effector genes [24, 25]. However, in P. syringae pv. syringae B728a, GacA appears not to be required for hrp gene expression [25]. The mgo operon is composed of four genes, mgoBCAD[4, 7]. Mutants in each gene belonging to the mgo operon showed an alteration (mgoB mutant) or lack of mangotoxin production (mgoC, mgoA and mgoD mutants). These genes GDC-0994 mw encode for different hypothetical proteins with predicted domains for a haem oxygenase (MgoB), a p-aminobenzoate N-oxygenase (MgoC), a nonribosomal peptide synthetase (MgoA), and a polyketide cyclase/dehydrase or lipid transporter (MgoD) [4, 7]. The predicted amino MI-503 purchase acid sequence of MgoA suggests only one amino acid activation module and 14 conserved domains, including aminoacyl adenylation, condensation, thiolation, and additional

reduction domains [4]. Genes homologous to the mgo operon have been found in the genomes of most Pseudomonas spp., with the exception of P. protegens Pf-5 and CHAO [26, 27]. Recent studies on the pvf gene cluster in P. entomophila, a homologue of the mgo operon, suggested that it affects virulence [28]. Almost all the fluorescent Pseudomonas spp. lack the mbo operon [29, 30], but the mgo operon is conserved in all of them (except P. protegens Pf-5) [4, 7, 26–28]. To date, however, the functions of mgo operon are yet unknown. The overall objective of this study was

to get insight into the role of the mgo operon in regulation of mangotoxin production in P. syringae pv. syringae UMAF0158 and unravel the interplay between mgo, mbo and the gacS/gacA two-component regulatory system. Methods Bacterial strains and culture conditions The wild type strain P. syringae pv. syringae UMAF0158 (CECT 7752) and the collection of selected derivative mutants used in this study (Table 1) were grown on Pseudomonas agar F (Difco) plates, in liquid King’s medium B (KMB) [31] or in Pseudomonas minimal medium Resveratrol (PMS) [32] at 28°C. Escherichia coli strain DH5α was used as a host for plasmid complementation experiments. It was routinely grown on Luria-Bertani (LB) plates or in LB broth at 37°C. Antibiotics for selection of P. syringae pv. syringae UMAF0158 and E. coli derivatives were ampicillin (100 mg L-1), kanamycin (50 mg L-1), gentamycin (30 mg L-1) or tetracycline (25 mg L-1). Table 1 Bacterial strains and plasmids used in this study Strain or plasmid Relevant characteristics Reference/source Strains     E. coli     DH5α E. coli [F’ Φ80lacZ ∆M15 ∆(lacZYA-argF)U169 deoR recA endA1 hsdR17 (rK-mK+)phoA supE44 lambda- thi-1] [33] CECT831 Indicator strain for mangotoxin production CECTa P. syringae pv.