title: Integration Host Factor (IHF) binds to the promoter region of the phtD operon involved in phaseolotoxin synthesis in P. syringae pv. phaseolicola NPS3121.
abstract: BACKGROUND
  Pseudomonas syringae pv. phaseolicola, the causal agent of halo blight disease in beans, produces a toxin known as phaseolotoxin, in whose synthesis participate a group of genes organized within the genome in a region known as the "Pht cluster". This region, which is thought to have been acquired by horizontal gene transfer, includes 5 transcriptional units, two monocistronic (argK, phtL) and three polycistronic (phtA, phtD, phtM), whose expression is temperature dependent. So far, the regulatory mechanisms involved in phaseolotoxin synthesis have not been elucidated and the only well-established fact is the requirement of low temperatures for its synthesis. In this work, we searched for regulatory proteins that could be involved in phaseolotoxin synthesis, focusing on the regulation of the phtD operon.
  
  
  RESULTS
  In this study we identified the global regulator IHF (Integration Host Factor), which binds to the promoter region of the phtD operon, exerting a negative effect on the expression of this operon. This is the first regulatory protein identified as part of the phaseolotoxin synthesis system. Our findings suggest that the Pht cluster was similarly regulated in the ancestral cluster by IHF or similar protein, and integrated into the global regulatory mechanism of P. syringae pv. phaseolicola, after the horizontal gene transfer event by using the host IHF protein.
  
  
  CONCLUSIONS
  This study identifies the IHF protein as one element involved in the regulation of phaseolotoxin synthesis in P. syringae pv. phaseolicola NPS3121 and provides new insights into the regulatory mechanisms involved in phaseolotoxin production.
authors.affiliation: Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional Unidad Irapuato, Apdo Postal 629, CP 36821, Irapuato, Gto, México.
authors.forename: Jackeline Lizzeta
authors.initials: JL
authors.lastname: Arvizu-Gómez
authors.forename: Alejandro
authors.initials: A
authors.lastname: Hernández-Morales
authors.forename: Guillermo
authors.initials: G
authors.lastname: Pastor-Palacios
authors.forename: Luis G
authors.initials: LG
authors.lastname: Brieba
authors.forename: Ariel
authors.initials: A
authors.lastname: Álvarez-Morales
mesh_terms: D004269:DNA, Bacterial / Q000378:metabolism*; D015536:Down-Regulation; D015964:Gene Expression Regulation, Bacterial; D034982:Integration Host Factors / Q000378:metabolism*; D009876:Operon; D009952:Ornithine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D044224:Pseudomonas syringae / Q000235:genetics* / Q000378:metabolism*
chemical_list: D004269:DNA, Bacterial; D034982:Integration Host Factors; C021234:phaseolotoxin; D009952:Ornithine