Characterization of the hrp pathogenicity cluster of Erwinia carotovora subsp. carotovora: high basal level expression in a mutant is associated with reduced virulence

Lehtimäki, Sari; Rantakari, Anssi; Routtu, Jarkko; Tuikkala, A.; Li, J.; Virtaharju, O.; Palva, E. Tapio; Romantschuk, Martin; Saarilahti, Hannu T.

doi:10.1007/s00438-003-0905-4

Cited by 18 publications

(15 citation statements)

References 51 publications

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“…Research into this phenomenon is further complicated by the fact that plasmids and cosmids expressing rsp structural genes and rsp regulators also impair growth of P. fluorescens SBW25 and rsp mutants (33; R. Jackson, G. Preston, and P. Rainey, unpublished), indicating that the stoichiometry and expression levels of rsp-encoded proteins are tightly regulated in SBW25. This effect has also been noted for Erwinia carotovora (25).…”

Section: Discussionsupporting

confidence: 68%

Genetic Characterization ofPseudomonas fluorescensSBW25rspGene Expression in the Phytosphere and In Vitro

2005

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The plant-colonizing Pseudomonas fluorescens strain SBW25 harbors a gene cluster (rsp) whose products show similarity to type III protein secretion systems found in plant and animal pathogens. Here we report a detailed analysis of the expression and regulation of the P. fluorescens rsp pathway, both in the phytosphere and in vitro. A combination of chromosomally integrated transcriptional reporter fusions, overexpressed regulatory genes, and specific mutants reveal that promoters controlling expression of rsp are actively transcribed in the plant rhizosphere but not (with the exception of the rspC promoter) in the phyllosphere. In synthetic medium, regulatory (rspL and rspR) and structural (rspU, plus the putative effector ropE) genes are poorly expressed; the rspC promoter is subject to an additional level of regulatory control. Ectopic expression of regulatory genes in wild-type and mutant backgrounds showed that RspR controls transcription of the alternate sigma factor, rspL, and that RspL controls expression of gene clusters encoding structural genes. Mutation of rspV did not affect RspR-mediated expression of rspU. A search for additional regulators revealed two candidates-one with a role in the conversion of alanine to pyruvate-suggesting that expression of rsp is partly dependent upon the metabolic status of the cell. Mutations in rsp regulators resulted in a significant reduction in competitive colonization of the root tips of sugar beet seedlings but also caused a marked increase in the lag phase of laboratory-grown cultures, indicating that rsp regulatory genes play a more significant general role in the function of P. fluorescens SBW25 than previously appreciated.The plant rhizosphere is a complex environment comprising organic matter and a plethora of microbes, some of which can affect plant health. Pathogens, such as Pythium ultimum, can hinder plant growth, whereas strains of Pseudomonas fluorescens, including P. fluorescens SBW25, can promote plant growth. The mechanism of plant growth promotion involves a combination of competition, antagonism of pathogens via the production of antimicrobial compounds, and induction of systemic resistance (15,16,31,34).To understand the interaction between P. fluorescens SBW25 and plants, SBW25 genes specifically activated in the plant environment were identified via a promoter trapping strategy (11,36). Approximately 100 rhizosphere-induced (rhi) genes have been identified and categorized into six groups: nutrient acquisition, stress response, attachment and surface colonization, antibiotic production, secretion, and unknown. One rhi gene (rhi-18) is hrcC (redesignated rscC), whose product is a component of a type III protein secretion system (TTSS) termed Rsp (33, 36) (Fig. 1).The P. fluorescens SBW25 rsp cluster exhibits a high level of synteny to the group I TTSS clusters of Pseudomonas syringae pv. tomato DC3000 and Erwinia amylovora and is genetically most similar to the P. syringae cluster. The cluster is organized into three putative transcriptional units...

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Section: Discussionsupporting

confidence: 68%

Genetic Characterization ofPseudomonas fluorescensSBW25rspGene Expression in the Phytosphere and In Vitro

2005

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“…dspA is dependent on HrpL for expression and is required for virulence (58). In addition to E. amylovora, several other members of the Erwinia genus carry hrpL and other hrp genes, including the tumorigenic pathogen Erwinia herbicola (149,155,156) and the soft-rot pathogens Erwinia carotovora (24,125,180) and Erwinia chrysanthemi (6). The hrp-encoded type III secretion system is thus a common virulence mechanism among plant pathogens and is widespread among several types of pathogens, including tumorigenic, macerating, and soft-rot-causing species.…”

Section: Hrplmentioning

confidence: 99%

Alternative Sigma Factors and Their Roles in Bacterial Virulence

Kazmierczak

Wiedmann

Boor

2005

Microbiol Mol Biol Rev

320

317

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SUMMARY Sigma factors provide promoter recognition specificity to RNA polymerase holoenzyme, contribute to DNA strand separation, and then dissociate from the core enzyme following transcription initiation. As the regulon of a single sigma factor can be composed of hundreds of genes, sigma factors can provide effective mechanisms for simultaneously regulating expression of large numbers of prokaryotic genes. One newly emerging field is identification of the specific roles of alternative sigma factors in regulating expression of virulence genes and virulence-associated genes in bacterial pathogens. Virulence genes encode proteins whose functions are essential for the bacterium to effectively establish an infection in a host organism. In contrast, virulence-associated genes can contribute to bacterial survival in the environment and therefore may enhance the capacity of the bacterium to spread to new individuals or to survive passage through a host organism. As alternative sigma factors have been shown to regulate expression of both virulence and virulence-associated genes, these proteins can contribute both directly and indirectly to bacterial virulence. Sigma factors are classified into two structurally unrelated families, the σ70 and the σ54 families. The σ70 family includes primary sigma factors (e.g., Bacillus subtilis σA) as well as related alternative sigma factors; σ54 forms a distinct subfamily of sigma factors referred to as σN in almost all species for which these proteins have been characterized to date. We present several examples of alternative sigma factors that have been shown to contribute to virulence in at least one organism. For each sigma factor, when applicable, examples are drawn from multiple species.

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“…Although these enzymes are required for development of symptoms, many other virulence genes have been shown to contribute to Pectobacterium pathogenicity, including the type III secretion system (T3SS) genes, the cfa gene cluster, and the type IV secretion system genes (3,15,19). Recent genomic analysis showed that some of these gene clusters, such as the cfa and type IV secretion system cluster genes, as well as genes important for interactions with insects, are present in only some Pectobacterium species (10).…”

Section: Brasiliensismentioning

confidence: 99%

Phylogeny and Virulence of Naturally Occurring Type III Secretion System-Deficient Pectobacterium Strains

Kim¹,

Perna

et al. 2009

Appl Environ Microbiol

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Pectobacterium species are enterobacterial plant-pathogenic bacteria that cause soft rot disease in diverse plant species. Previous epidemiological studies of Pectobacterium species have suffered from an inability to identify most isolates to the species or subspecies level. We used three previously described DNA-based methods, 16S-23S intergenic transcribed spacer PCR-restriction fragment length polymorphism analysis, multilocus sequence analysis (MLSA), and pulsed-field gel electrophoresis, to examine isolates from diseased stems and tubers and found that MLSA provided the most reliable classification of isolates. We found that strains belonging to at least two Pectobacterium clades were present in each field examined, although representatives of only three of five Pectobacterium clades were isolated. Hypersensitive response and DNA hybridization assays revealed that strains of both Pectobacterium carotovorum and Pectobacterium wasabiae lack a type III secretion system (T3SS). Two of the T3SS-deficient strains assayed lack genes adjacent to the T3SS gene cluster, suggesting that multiple deletions occurred in Pectobacterium strains in this locus, and all strains appear to have only six rRNA operons instead of the seven operons typically found in Pectobacterium strains. The virulence of most of the T3SS-deficient strains was similar to that of T3SS-encoding strains in stems and tubers.The genus Pectobacterium (formerly Erwinia) contains both narrow-and broad-host-range bacterial plant pathogens that cause soft rot, stem rot, wilt, and blackleg in species belonging to over 35% of plant orders (20). Four Pectobacterium species have been described: Pectobacterium atrosepticum, Pectobacterium betavasculorum, Pectobacterium carotovorum, and Pectobacterium wasabiae (9). The recently described organism P. carotovorum subsp. brasiliensis is genetically distinct from previously described Pectobacterium taxa; approximately 82% of its genes are shared with P. atrosepticum, and 84% of its genes are shared with P. carotovorum subsp. carotovorum, while 13% of its genes are found in neither P. atrosepticum nor P. carotovorum subsp. carotovorum (7,10,20). To date, only P. carotovorum subsp. carotovorum and P. atrosepticum have been reported to occur in the same field (14, 21). P. carotovorum subsp. carotovorum is found worldwide, and P. atrosepticum is found in cool climates; while P. carotovorum subsp. brasiliensis has been found only in Brazil, Israel, and the United States, it is likely to have a wider distribution (20). Compared to the ecology and genetics of P. carotovorum subsp. carotovorum and P. atrosepticum, little is known about the ecology and genetics of P. betavasculorum, P. wasabiae, or P. carotovorum subsp. brasiliensis.Pectobacterium strains isolated from potato are diverse based on serology, genome structure, and fatty acid composition (5, 35). Previous epidemiological studies of pectolytic Enterobacteriaceae were complicated by the diversity of this group and the lack of tools capable of placing all isolates ...

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Characterization of the hrp pathogenicity cluster of Erwinia carotovora subsp. carotovora: high basal level expression in a mutant is associated with reduced virulence

Cited by 18 publications

References 51 publications

Genetic Characterization ofPseudomonas fluorescensSBW25rspGene Expression in the Phytosphere and In Vitro

Genetic Characterization ofPseudomonas fluorescensSBW25rspGene Expression in the Phytosphere and In Vitro

Alternative Sigma Factors and Their Roles in Bacterial Virulence

Phylogeny and Virulence of Naturally Occurring Type III Secretion System-Deficient Pectobacterium Strains

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