title: Characterization of the transcriptional activators SalA and SyrF, Which are required for syringomycin and syringopeptin production by Pseudomonas syringae pv. syringae.
abstract: Production of the phytotoxins syringomycin and syringopeptin by Pseudomonas syringae pv. syringae is controlled by the regulatory genes salA and syrF. Analysis with 70-mer oligonucleotide microarrays established that the syr-syp genes responsible for synthesis and secretion of syringomycin and syringopeptin belong to the SyrF regulon. Vector pMEKm12 was successfully used to express both SalA and SyrF proteins fused to a maltose-binding protein (MBP) in Escherichia coli and P. syringae pv. syringae. Both the MBP-SalA and MBP-SyrF fusion proteins were purified by maltose affinity chromatography. Gel shift analysis revealed that the purified MBP-SyrF, but not the MBP-SalA fusion protein, bound to a 262-bp fragment of the syrB1 promoter region containing the syr-syp box. Purified MBP-SalA caused a shift of a 324-bp band containing the putative syrF promoter. Gel filtration analysis and cross-linking experiments indicated that both SalA and SyrF form homodimers in vitro. Overexpression of the N-terminal regions of SalA and SyrF resulted in decreased syringomycin production by strain B301D and reduced levels of beta-glucuronidase activities of the sypA::uidA and syrB1::uidA reporters by 59% to 74%. The effect of SalA on the expression of the syr-syp genes is mediated by SyrF, which activates the syr-syp genes by directly binding to the promoter regions. Both SalA and SyrF resemble other LuxR family proteins in dimerization and interaction with promoter regions of target genes.
authors.affiliation: Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843, USA.
authors.forename: Nian
authors.initials: N
authors.lastname: Wang
authors.forename: Shi-En
authors.initials: SE
authors.lastname: Lu
authors.forename: Angela R
authors.initials: AR
authors.lastname: Records
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Gross
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000096:biosynthesis* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D019281:Dimerization; D024202:Electrophoretic Mobility Shift Assay; D015967:Gene Expression Regulation, Viral; D005798:Genes, Bacterial / Q000235:genetics; D005966:Glucuronidase / Q000378:metabolism; D010456:Peptides, Cyclic / Q000096:biosynthesis* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D044224:Pseudomonas syringae / Q000235:genetics* / Q000378:metabolism; D018085:Regulon / Q000235:genetics; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004268:DNA-Binding Proteins; D010456:Peptides, Cyclic; C114405:SalA protein, Pseudomonas syringae; D015534:Trans-Activators; D014157:Transcription Factors; C032677:syringomycin; D005966:Glucuronidase