title: Phylogenetic analysis of a gene cluster encoding an additional, rhizobial-like type III secretion system that is narrowly distributed among Pseudomonas syringae strains.
abstract: BACKGROUND
  The central role of Type III secretion systems (T3SS) in bacteria-plant interactions is well established, yet unexpected findings are being uncovered through bacterial genome sequencing. Some Pseudomonas syringae strains possess an uncharacterized cluster of genes encoding putative components of a second T3SS (T3SS-2) in addition to the well characterized Hrc1 T3SS which is associated with disease lesions in host plants and with the triggering of hypersensitive response in non-host plants. The aim of this study is to perform an in silico analysis of T3SS-2, and to compare it with other known T3SSs.
  
  
  RESULTS
  Based on phylogenetic analysis and gene organization comparisons, the T3SS-2 cluster of the P. syringae pv. phaseolicola strain is grouped with a second T3SS found in the pNGR234b plasmid of Rhizobium sp. These additional T3SS gene clusters define a subgroup within the Rhizobium T3SS family. Although, T3SS-2 is not distributed as widely as the Hrc1 T3SS in P. syringae strains, it was found to be constitutively expressed in P. syringae pv phaseolicola through RT-PCR experiments.
  
  
  CONCLUSIONS
  The relatedness of the P. syringae T3SS-2 to a second T3SS from the pNGR234b plasmid of Rhizobium sp., member of subgroup II of the rhizobial T3SS family, indicates common ancestry and/or possible horizontal transfer events between these species. Functional analysis and genome sequencing of more rhizobia and P. syringae pathovars may shed light into why these bacteria maintain a second T3SS gene cluster in their genome.
authors.affiliation: Department of Biology, University of Crete, Vasilika Vouton, P,O, Box 2208, Heraklion, Crete GR 71409, Greece.
authors.forename: Anastasia D
authors.initials: AD
authors.lastname: Gazi
authors.forename: Panagiotis F
authors.initials: PF
authors.lastname: Sarris
authors.forename: Vasiliki E
authors.initials: VE
authors.lastname: Fadouloglou
authors.forename: Spyridoula N
authors.initials: SN
authors.lastname: Charova
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Mathioudakis
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Panopoulos
authors.forename: Michael
authors.initials: M
authors.lastname: Kokkinidis
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics*; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D023061:Gene Order; D022761:Gene Transfer, Horizontal; D005810:Multigene Family; D010802:Phylogeny; D010957:Plasmids; D044224:Pseudomonas syringae / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012231:Rhizobium / Q000235:genetics; D026801:Synteny
chemical_list: D058947:Bacterial Secretion Systems