Phylogenetic analysis of a gene cluster encoding an additional, rhizobial-like type III secretion system that is narrowly distributed among Pseudomonas syringae strains

Abstract

BackgroundThe 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.ResultsBased 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.ConclusionsThe 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.

Comprehensive analysis of draft genomes of two closely related pseudomonas syringae phylogroup 2b strains infecting mono- and dicotyledon host plants

“…The main function of T3SS is the delivery of effector proteins into the cell body of a host [37–39]. In all the studied strains, there is a fully functional cluster T3SS-1 comprised of 15 genes and all of the 9 key genes are present.…”

Assembly of the bacterial type III secretion machinery

“…The so-called MS ring (membrane and supramembrane) in the IM is formed by a lipoprotein that constitutes the inner side of the ring (SctJ) (Kimbrough & Miller, 2000;Crepin et al, 2005;Yip et al, 2005;Silva-Herzog et al, 2008), and a single-spanning transmembrane protein constituting the outside (SctD) (Kimbrough & Miller, 2000;Spreter et al, 2009; McDo- Table 1. Homologous proteins and their function in various families of T3SS and the flagellum (Hueck, 1998;Meyer et al, 2006;H€ olzer & Hensel, 2010;Abby & Rocha, 2012;B€ uttner, 2012;Gazi et al, 2012 Protein names are given for well-studied members of the respective T3SS families. The degree of conservation is represented by the similarity score of the consensus sequence determined by the multiple sequence alignment package M-Coffee (Wallace et al, 2006) for the respective homologues of Yersinia enterocolitica virulence plasmid pYVe227 (for Ysc), Salmonella enterica spp.…”

Behind the lines–actions of bacterial type III effector proteins in plant cells

“…In addition to the Hrp1 T3S system, some P. syringae strains also contain a rhizobial-like T3S system, designated Hrp3 (Gazi et al. 2012). Interestingly, gene clusters with homologies to T3S gene clusters from plant-pathogenic bacteria are also present in several animal-pathogenic bacteria including Vibrio parahaemolyticus strains isolated from patients, a clinical strain of Pantoea , and Burkholderia pseudomallei (Troisfontaines and Cornelis 2005; Kirzinger, Butz and Stavrinides 2015).…”