The alternative sigma factor AlgT, but not alginate synthesis, promotes in planta multiplication of Pseudomonas syringae pv. glycinea

Schenk, Alexander; Weingart, Helge; Ullrich, Matthias S.

doi:10.1099/mic.0.2007/012864-0

Cited by 32 publications

(23 citation statements)

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“…tomato DC3000 AlgU promotes disease and in planta growth. The function of alginate and AlgU in P. syringae plant disease has been tested previously (19,21,30). The results of these studies suggest that there is variability regarding the role of alginate and AlgU in promoting P. syringae virulence and growth in plants.…”

Section: Resultsmentioning

confidence: 70%

“…In contrast, P. syringae pv. glycinea PG4180, which causes bacterial blight on soybean, is not dependent on alginate production, but the presence of algU has a positive effect on virulence and bacterial growth in host plants (19,21). Similarly, epiphytic and endophytic growths are reduced for P. syringae pv.…”

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confidence: 97%

“…The proposed functions of alginate in planta include water absorption and nutrient acquisition, protection from antimicrobial compounds, protection from osmotic and oxidative stress, Ca 2ϩ sequestration, and suppression of host defenses (27)(28)(29). However, the degree of the effect that alginate has on plant disease may depend on details of the specific interaction between individual P. syringae strains and plant hosts (19,21,30). For example, alginate production by P. syringae pv.…”

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confidence: 99%

“…tomato DC3000 contains all of the genes necessary for alginate production but lacks homologs to some of the regulatory genes found in P. aeruginosa (15,16), and there are some differences with regard to the environmental stimuli that activate alginate production in these bacteria (17). In P. syringae, AlgU autoregulates its own expression and that of algD (18)(19)(20). Keith and Bender reported that P. syringae pv.…”

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AlgU Controls Expression of Virulence Genes in Pseudomonas syringae pv. tomato DC3000

et al. 2016

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Plant-pathogenic bacteria are able to integrate information about their environment and adjust gene expression to provide adaptive functions. AlgU, an extracytoplasmic function (ECF) sigma factor encoded by Pseudomonas syringae, controls expression of genes for alginate biosynthesis and genes involved with resisting osmotic and oxidative stress. AlgU is active while these bacteria are associated with plants, where its presence supports bacterial growth and disease symptoms. We found that AlgU is an important virulence factor for P. syringae pv. tomato DC3000 but that alginate production is dispensable for disease in host plants. This implies that AlgU regulates additional genes that facilitate bacterial pathogenesis. We used transcriptome sequencing (RNA-seq) to characterize the AlgU regulon and chromatin immunoprecipitation sequencing (ChIP-seq) to identify AlgUregulated promoters associated with genes directly controlled by this sigma factor. We found that in addition to genes involved with alginate and osmotic and oxidative stress responses, AlgU regulates genes with known virulence functions, including components of the Hrp type III secretion system, virulence effectors, and the hrpL and hrpRS transcription regulators. These data suggest that P. syringae pv. tomato DC3000 has adapted to use signals that activate AlgU to induce expression of important virulence functions that facilitate survival and disease in plants. IMPORTANCEPlant immune systems produce antimicrobial and bacteriostatic conditions in response to bacterial infection. Plant-pathogenic bacteria are adapted to suppress and/or tolerate these conditions; however, the mechanisms controlling these bacterial systems are largely uncharacterized. The work presented here provides a mechanistic explanation for how P. syringae pv. tomato DC3000 coordinates expression of multiple genetic systems, including those dedicated to pathogenicity, in response to environmental conditions. This work demonstrates the scope of AlgU regulation in P. syringae pv. tomato DC3000 and characterizes the promoter sequence regulated by AlgU in these bacteria. Pseudomonas syringae is a globally dispersed plant-pathogenic bacterium adapted to live in many diverse environments, which in some cases expose bacteria to stresses that can interfere with their growth and survival. Counteracting or tolerating these stresses requires coordinated expression of specific physiologic traits. These responses are controlled by environmental sensing and signal transduction systems that detect information about external conditions and induce changes in transcription. The extracytoplasmic function (ECF) sigma factors are one type of system providing this function in bacteria and are capable of inducing sets of genes (regulons) in response to environmental stimuli (1). ECF sigma factor activity is often controlled by a cytoplasmic membrane-bound anti-sigma factor that forms a complex with the ECF sigma factor (2). Under inducing conditions, the ECF sigma factor is liberated from the anti-...

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confidence: 70%

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confidence: 97%

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confidence: 99%

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AlgU Controls Expression of Virulence Genes in Pseudomonas syringae pv. tomato DC3000

et al. 2016

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“…Some of the alginate biosynthesis and regulatory genes in P. syringae, a plant pathogen that utilizes environmental signals such as copper to trigger alginate production, have been studied (10,18). However, in P. syringae, the expression of the alginate transcriptional regulator AlgT, rather than alginate production alone, is required for virulence (33). Amino acid comparisons of AmrZ with its proposed orthologs PP4470 (P. putida) and PSPTO1847 (P. syringae pv.…”

Section: Discussionmentioning

confidence: 99%

AmrZ Beta-Sheet Residues Are Essential for DNA Binding and Transcriptional Control of Pseudomonas aeruginosa Virulence Genes

Waligora¹,

Ramsey²,

Pryor

et al. 2010

J Bacteriol

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AmrZ is a putative ribbon-helix-helix (RHH) transcriptional regulator. RHH proteins utilize residues within the ␤-sheet for DNA binding, while the ␣-helices promote oligomerization. AmrZ is of interest due to its dual roles as a transcriptional activator and as a repressor, regulating genes encoding virulence factors associated with both chronic and acute Pseudomonas aeruginosa infection. In this study, cross-linking revealed that AmrZ forms oligomers in solution but that the amino terminus, containing an unordered region and a ␤-sheet, were not required for oligomerization. The first 12 unordered residues (extended amino terminus) contributed minimally to DNA binding. Mutagenesis of the AmrZ ␤-sheet demonstrated that residues 18, 20, and 22 were essential for DNA binding at both activation and repressor sites, suggesting that AmrZ utilizes a similar mechanism for binding to these sites. Mice infected with amrZ mutants exhibited reduced bacterial burden, morbidity, and mortality. Direct in vivo competition assays showed a 5-fold competitive advantage for the wild type over an isogenic amrZ mutant. Finally, the reduced infection phenotype of the amrZ-null strain was similar to that of a strain expressing a DNA-binding-deficient AmrZ variant, indicating that DNA binding and transcriptional regulation by AmrZ is responsible for the in vivo virulence defect. These recent infection data, along with previously identified AmrZ-regulated virulence factors, suggest the necessity of AmrZ transcriptional regulation for optimal virulence during acute infection.The Pseudomonas aeruginosa transcriptional regulator AmrZ is a proposed member of the ribbon-helix-helix (RHH) family of DNA-binding proteins, sharing structural similarity with the Arc and Mnt repressors of Salmonella enterica serovar Typhimurium bacteriophage P22. This family is grouped by structural similarity and includes several transcriptional regulators found in prokaryotes, archaea and their viruses, and other bacteriophages (2,7,12,20,24,26,34,46). Based on amino acid identity as well as secondary-structure prediction models, AmrZ likely possesses a ribbon-helix-helix motif (i.e., one ␤-strand and two ␣-helices) (Fig. 1B) responsible for DNA-binding activity in this family of proteins (44). RHH proteins function through the oligomerization of the ␣-helices, which allows the two ␤-strands to form an antiparallel ␤-sheet that recognizes and binds in the major groove of the operator site (31, 38). Arc exists as a dimer in solution, while Mnt utilizes an extra carboxy-terminal ␣-helical domain to maintain a tetramer configuration (43). When binding DNA, these oligomers are maintained, and the inhibition of oligomerization negatively impacts DNA-binding activity (44). To facilitate higher-order oligomers at the RHH binding site, operator sites often contain sequences in either a direct repeat or palindromic orientation (34,46). Because there are specific contacts between residues of the DNA-binding ␤-sheet and bases in the operator site, mutations of critical base...

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Motility, Biofilm Formation, and Rhizosphere Colonization byPseudomonas fluorescensF113

Rivilla

Martínez‐Granero

Martín

2013

Molecular Microbial Ecology of the Rhizosphere

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The alternative sigma factor AlgT, but not alginate synthesis, promotes in planta multiplication of Pseudomonas syringae pv. glycinea

Cited by 32 publications

References 47 publications

AlgU Controls Expression of Virulence Genes in Pseudomonas syringae pv. tomato DC3000

AlgU Controls Expression of Virulence Genes in Pseudomonas syringae pv. tomato DC3000

AmrZ Beta-Sheet Residues Are Essential for DNA Binding and Transcriptional Control of Pseudomonas aeruginosa Virulence Genes

Motility, Biofilm Formation, and Rhizosphere Colonization byPseudomonas fluorescensF113

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