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Abstract
Pseudomonas syringae is one of the best-studied plant pathogens and serves as a model for understanding host-microorganism interactions, bacterial virulence mechanisms and host adaptation of pathogens as well as microbial evolution, ecology and epidemiology. Comparative genomic studies have identified key genomic features that contribute to P. syringae virulence. P. syringae has evolved two main virulence strategies: suppression of host immunity and creation of an aqueous apoplast to form its niche in the phyllosphere. In addition, external environmental conditions such as humidity profoundly influence infection. P. syringae may serve as an excellent model to understand virulence and also of how pathogenic microorganisms integrate environmental conditions and plant microbiota to become ecologically robust and diverse pathogens of the plant kingdom.
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Aguilera S, Alvarez-Morales A, Murillo J, Hernández-Flores JL, Bravo J, De la Torre-Zavala S. Temperature-mediated biosynthesis of the phytotoxin phaseolotoxin by Pseudomonas syringae pv. phaseolicola depends on the autoregulated expression of the phtABC genes. PLoS One 2017; 12:e0178441. [PMID: 28570637 PMCID: PMC5453526 DOI: 10.1371/journal.pone.0178441] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 05/12/2017] [Indexed: 11/18/2022] Open
Abstract
Pseudomonas syringae pv. phaseolicola produces phaseolotoxin in a temperature dependent manner, being optimally synthesized between 18°C and 20°C, while no detectable amounts are present above 28°C. The Pht cluster, involved in the biosynthesis of phaseolotoxin, contains 23 genes that are organized in five transcriptional units. The function of most of the genes from the Pht cluster is still unknown and little information about the regulatory circuitry leading to expression of these genes has been reported. The purpose of the present study was to investigate the participation of pht genes in the regulation of the operons coded into the Pht cluster. We conducted Northern blot, uidA fusions and reverse transcription-PCR assays of pht genes in several mutants unable to produce phaseolotoxin. This allowed us to determine that, in P. syringae pv. phaseolicola NPS3121, genes phtABC are essential to prevent their own expression at 28°C, a temperature at which no detectable amounts of the toxin are present. We obtained evidence that the phtABC genes also participate in the regulation of the phtD, phtM and phtL operons. According to our results, we propose that PhtABC and other Pht product activities could be involved in the synthesis of the sulfodiaminophosphinyl moiety of phaseolotoxin, which indirectly could be involved in the transcriptional regulation of the phtA operon.
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Affiliation(s)
- Selene Aguilera
- Laboratorio Integral de Investigación en Alimentos. CONACYT-Instituto Tecnológico de Tepic, Tepic, Nayarit, México
- * E-mail:
| | - Ariel Alvarez-Morales
- Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados (CINVESTAV), Irapuato, Guanajuato, México
| | - Jesús Murillo
- Departamento de Producción Agraria, Universidad Pública de Navarra, Pamplona, Spain
| | - José Luis Hernández-Flores
- Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados (CINVESTAV), Irapuato, Guanajuato, México
| | - Jaime Bravo
- Laboratorio Integral de Investigación en Alimentos. Instituto Tecnológico de Tepic, Tepic, Nayarit, México
| | - Susana De la Torre-Zavala
- Instituto de Biotecnología, Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, Monterrey, Nuevo León, México
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3
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Construction of a Pseudomonas aeruginosa genomic DNA library. Methods Mol Biol 2014. [PMID: 24818932 DOI: 10.1007/978-1-4939-0473-0_42] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Although the completion and annotation of the entire genomic DNA sequence of Pseudomonas aeruginosa PAO1 strain has been carried out, an important number of genes are still of unknown function and many genetic elements involved in various regulatory pathways like small RNA are still unrevealed. One of the strategies to identify gene function or genetic elements is the construction and utilization of DNA genomic library. Here, we describe the construction a P. aeruginosa DNA genomic library.
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Abstract
Temperature, among other environmental factors, influences the incidence and severity of many plant diseases. Likewise, numerous traits, including the expression of virulence factors, are regulated by temperature. Little is known about the underlying genetic determinants of thermoregulation in plant-pathogenic bacteria. Previously, we showed that the expression of both fliC (encoding flagellin) and syfA (encoding a nonribosomal polypeptide synthetase) was suppressed at high temperatures in Pseudomonas syringae. In this work, we used a high-throughput screen to identify mutations that conferred overexpression of syfA at elevated temperatures (28°C compared to 20°C). Two genes, Psyr_2474, encoding an acyl-coenzyme A (CoA) dehydrogenase, and Psyr_4843, encoding an ortholog of RppH, which in Escherichia coli mediates RNA turnover, contribute to thermoregulation of syfA. To assess the global role of rppH in thermoregulation in P. syringae, RNA sequencing was used to compare the transcriptomes of an rppH deletion mutant and the wild-type strain incubated at 20°C and 30°C. The disruption of rppH had a large effect on the temperature-dependent transcriptome of P. syringae, affecting the expression of 569 genes at either 20°C or 30°C but not at both temperatures. Intriguingly, RppH is involved in the thermoregulation of ribosome-associated proteins, as well as of RNase E, suggesting a prominent role of rppH on the proteome in addition to its effect on the transcriptome.
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Expression of the gene for resistance to phaseolotoxin (argK) depends on the activity of genes phtABC in Pseudomonas syringae pv. phaseolicola. PLoS One 2012; 7:e46815. [PMID: 23056465 PMCID: PMC3466206 DOI: 10.1371/journal.pone.0046815] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Accepted: 09/05/2012] [Indexed: 11/19/2022] Open
Abstract
The bacterium Pseudomonas syringae pv. phaseolicola produces phaseolotoxin in a temperature dependent manner, being optimally produced between 18°C and 20°C, while no detectable amounts are present above 28°C. Phaseolotoxin is an effective inhibitor of ornithine carbamoyltransferase (OCTase) activity from plant, mammalian and bacterial sources and causes a phenotypic requirement for arginine. To protect the cell from its own toxin, P. syringae pv. phaseolicola synthesizes a phaseolotoxin-resistant OCTase (ROCT). The ROCT is the product of the argK gene and is synthesized only under conditions leading to phaseolotoxin synthesis. The argK gene is included in a chromosomal fragment named Pht cluster, which contains genes involved in the synthesis of phaseolotoxin. The aim of the present work was to investigate the possible involvement of other genes included in the Pht cluster in the regulation of gene argK. We conducted transcriptional analyses of argK in several mutants unable to produce phaseolotoxin, transcriptional fusions and electrophoretic mobility shift assays, which allowed us to determine that genes phtABC, located within the Pht cluster, participate in the transcriptional repression of gene argK at temperatures not permissive for phaseolotoxin biosynthesis. This repression is mediated by a protein present in both toxigenic and nontoxigenic strains of P. syringae and in E. coli, and requires the coordinated participation of phtA, phtB and phtC products in order to carry out an efficient argK repression.
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Arrebola E, Cazorla FM, Pérez-García A, Vicente AD. Genes Involved in the Production of Antimetabolite Toxins by Pseudomonas syringae Pathovars. Genes (Basel) 2011; 2:640-60. [PMID: 24710214 PMCID: PMC3927611 DOI: 10.3390/genes2030640] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 09/06/2011] [Accepted: 09/06/2011] [Indexed: 11/30/2022] Open
Abstract
Pseudomonas syringae is pathogenic in a wide variety of plants, causing diseases with economic impacts. Pseudomonas syringae pathovars produce several toxins that can function as virulence factors and contribute to disease symptoms. These virulence factors include antimetabolite toxins, such as tabtoxin, phaseolotoxin and mangotoxin, which target enzymes in the pathways of amino acid metabolism. The antimetabolite toxins are generally located in gene clusters present in the flexible genomes of specific strains. These gene clusters are typically present in blocks of genes that appear to be integrated into specific sites in the P. syringae core genome. A general overview of the genetic organization and biosynthetic and regulatory functions of these genetic traits of the antimetabolite toxins will be given in the present work.
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Affiliation(s)
- Eva Arrebola
- Experimental Station La Mayora, Institute of Subtropical Horticulture and Mediterranean "La Mayora" (IHSM-UMA-CSIC), Algarrobo-Costa (Málaga) 29750, Spain.
| | - Francisco M Cazorla
- Microbiology Department, Institute of Subtropical Horticultural and Mediterranean "La Mayora" (IHSM-UMA-CSIC), Faculty of Science, University of Málaga, Associated Unit with the CSIC, Campus de Teatinos, Málaga 29071, Spain.
| | - Alejandro Pérez-García
- Microbiology Department, Institute of Subtropical Horticultural and Mediterranean "La Mayora" (IHSM-UMA-CSIC), Faculty of Science, University of Málaga, Associated Unit with the CSIC, Campus de Teatinos, Málaga 29071, Spain.
| | - Antonio de Vicente
- Microbiology Department, Institute of Subtropical Horticultural and Mediterranean "La Mayora" (IHSM-UMA-CSIC), Faculty of Science, University of Málaga, Associated Unit with the CSIC, Campus de Teatinos, Málaga 29071, Spain.
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Arrebola E, Cazorla FM, Perez-García A, de Vicente A. Chemical and metabolic aspects of antimetabolite toxins produced by Pseudomonas syringae pathovars. Toxins (Basel) 2011; 3:1089-110. [PMID: 22069758 PMCID: PMC3202874 DOI: 10.3390/toxins3091089] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Revised: 08/17/2011] [Accepted: 08/17/2011] [Indexed: 11/17/2022] Open
Abstract
Pseudomonas syringae is a phytopathogenic bacterium present in a wide variety of host plants where it causes diseases with economic impact. The symptoms produced by Pseudomonas syringae include chlorosis and necrosis of plant tissues, which are caused, in part, by antimetabolite toxins. This category of toxins, which includes tabtoxin, phaseolotoxin and mangotoxin, is produced by different pathovars of Pseudomonas syringae. These toxins are small peptidic molecules that target enzymes of amino acids' biosynthetic pathways, inhibiting their activity and interfering in the general nitrogen metabolism. A general overview of the toxins' chemistry, biosynthesis, activity, virulence and potential applications will be reviewed in this work.
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Affiliation(s)
- Eva Arrebola
- Instituto de Hortofruticultura Subtropical y Mediterránea “La Mayora” (IHSM-UMA-CSIC), Estación Experimental La Mayora, Algarrobo-Costa, Málaga 29750, Spain
| | - Francisco M. Cazorla
- Instituto de Hortofruticultura Subtropical y Mediterránea “La Mayora” (IHSM-UMA-CSIC), Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, Unidad Asociada al CSIC, Campus de Teatinos, Málaga 29071, Spain; (F.M.C.); (A.P.-G.); (A.V.)
| | - Alejandro Perez-García
- Instituto de Hortofruticultura Subtropical y Mediterránea “La Mayora” (IHSM-UMA-CSIC), Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, Unidad Asociada al CSIC, Campus de Teatinos, Málaga 29071, Spain; (F.M.C.); (A.P.-G.); (A.V.)
| | - Antonio de Vicente
- Instituto de Hortofruticultura Subtropical y Mediterránea “La Mayora” (IHSM-UMA-CSIC), Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, Unidad Asociada al CSIC, Campus de Teatinos, Málaga 29071, Spain; (F.M.C.); (A.P.-G.); (A.V.)
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Small RNAs as regulators of primary and secondary metabolism in Pseudomonas species. Appl Microbiol Biotechnol 2011; 91:63-79. [PMID: 21607656 DOI: 10.1007/s00253-011-3332-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 04/11/2011] [Accepted: 04/11/2011] [Indexed: 10/18/2022]
Abstract
Small RNAs (sRNAs) exert important functions in pseudomonads. Classical sRNAs comprise the 4.5S, 6S, 10Sa and 10Sb RNAs, which are known in enteric bacteria as part of the signal recognition particle, a regulatory component of RNA polymerase, transfer-messenger RNA (tmRNA) and the RNA component of RNase P, respectively. Their homologues in pseudomonads are presumed to have analogous functions. Other sRNAs of pseudomonads generally have little or no sequence similarity with sRNAs of enteric bacteria. Numerous sRNAs repress or activate the translation of target mRNAs by a base-pairing mechanism. Examples of this group in Pseudomonas aeruginosa are the iron-repressible PrrF1 and PrrF2 sRNAs, which repress the translation of genes encoding iron-containing proteins, and PhrS, an anaerobically inducible sRNA, which activates the expression of PqsR, a regulator of the Pseudomonas quinolone signal. Other sRNAs sequester RNA-binding proteins that act as translational repressors. Examples of this group in P. aeruginosa include RsmY and RsmZ, which are central regulatory elements in the GacS/GacA signal transduction pathway, and CrcZ, which is a key regulator in the CbrA/CbrB signal transduction pathway. These pathways largely control the extracellular activities (including virulence traits) and the selection of the energetically most favourable carbon sources, respectively, in pseudomonads.
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Arvizu-Gómez JL, Hernández-Morales A, Pastor-Palacios G, Brieba LG, Álvarez-Morales A. Integration Host Factor (IHF) binds to the promoter region of the phtD operon involved in phaseolotoxin synthesis in P. syringae pv. phaseolicola NPS3121. BMC Microbiol 2011; 11:90. [PMID: 21542933 PMCID: PMC3112066 DOI: 10.1186/1471-2180-11-90] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2011] [Accepted: 05/04/2011] [Indexed: 11/24/2022] Open
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. Conclusion 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.
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Affiliation(s)
- Jackeline Lizzeta Arvizu-Gómez
- 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
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10
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Valverde C, Haas D. Small RNAs Controlled by Two-Component Systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 631:54-79. [DOI: 10.1007/978-0-387-78885-2_5] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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11
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Lapouge K, Schubert M, Allain FHT, Haas D. Gac/Rsm signal transduction pathway of γ-proteobacteria: from RNA recognition to regulation of social behaviour. Mol Microbiol 2007; 67:241-53. [DOI: 10.1111/j.1365-2958.2007.06042.x] [Citation(s) in RCA: 440] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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12
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Aguilera S, López-López K, Nieto Y, Garcidueñas-Piña R, Hernández-Guzmán G, Hernández-Flores JL, Murillo J, Alvarez-Morales A. Functional characterization of the gene cluster from Pseudomonas syringae pv. phaseolicola NPS3121 involved in synthesis of phaseolotoxin. J Bacteriol 2007; 189:2834-43. [PMID: 17237165 PMCID: PMC1855804 DOI: 10.1128/jb.01845-06] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas syringae pv. phaseolicola is the causal agent of halo blight disease of beans (Phaseolus vulgaris L.), which is characterized by water-soaked lesions surrounded by a chlorotic halo resulting from the action of a non-host-specific toxin known as phaseolotoxin. This phytotoxin inhibits the enzyme ornithine carbamoyltransferase involved in arginine biosynthesis. Different evidence suggested that genes involved in phaseolotoxin production were clustered. Two genes had been previously identified in our laboratory within this cluster: argK, which is involved in the immunity of the bacterium to its own toxin, and amtA, which is involved in the synthesis of homoarginine. We sequenced the region around argK and amtA in P. syringae pv. phaseolicola NPS3121 to determine the limits of the putative phaseolotoxin gene cluster and to determine the transcriptional pattern of the genes comprising it. We report that the phaseolotoxin cluster (Pht cluster) is composed of 23 genes and is flanked by insertion sequences and transposases. The mutation of 14 of the genes within the cluster lead to a Tox(-) phenotype for 11 of them, while three mutants exhibited low levels of toxin production. The analysis of fusions of selected DNA fragments to uidA, Northern probing, and reverse transcription-PCR indicate the presence of five transcriptional units, two monocistronic and three polycistronic; one is internal to a larger operon. The site for transcription initiation has been determined for each promoter, and the putative promoter regions were identified. Preliminary results also indicate that the gene product of phtL is involved in the regulation of the synthesis of phaseolotoxin.
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Affiliation(s)
- Selene Aguilera
- Cinvestav, IPN Unidad Irapuato, Departamento de Ingeniería Genética, Irapuato, Gto., Apdo. Postal 629, CP 36500 Mexico
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Goyer C, Ullrich MS. Identification of low-temperature-regulated genes in the fire blight pathogen Erwinia amylovora. Can J Microbiol 2006; 52:468-75. [PMID: 16699572 DOI: 10.1139/w05-153] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Genes involved in pathogenicity of several plant pathogens were shown to be induced at relatively cold temperatures. Loci from the fire blight pathogen Erwinia amylovora (Burrill) induced at 18 degrees C were identified using the miniTn5 transposon that contains the promoterless reporter gene gusA coding for beta-glucuronidase (GUS). Certain mutants (2.7%) expressed GUS predominantly at 18 degrees C on minimal medium plates, indicating that the transposon had been inserted downstream of a putatively thermoregulated promoter. Those mutants were further screened with a quantitative GUS fluorometric assay. A total of 21 mutants were selected: 19 mutants had a transposon insertion in temperature-dependent genetic loci, with a 2.2- to 6.3-fold induction of gusA gene expression at 18 degrees C, and two mutants with impaired growth at 18 degrees C. Some of these genetic loci encoded (i) proteins implicated in flagella biosynthesis, biotin biosynthesis, multi-drug efflux, and type II secretion protein, and (ii) proteins of unknown function.
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Affiliation(s)
- Claudia Goyer
- Max-Planck-Institute for Terrestrial Microbiology, Marburg, Germany.
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14
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Abstract
Small regulatory RNAs can modify the activity of proteins and the stability and translation of mRNAs. They have now been found in a wide range of organisms, and can play previously unsuspected critical regulatory roles. The bacterial small RNAs include two major classes. The largest family(with at least 20 members in Escherichia coli K12) acts by base pairing with target mRNAs to modify mRNA translation or stability; this class of RNAs also uses an RNA chaperone protein, Hfq. DsrA is the best-studied example of this family of RNAs. It has been shown to positively regulate translation of the transcription factor RpoS by opening an inhibitory hairpin in the mRNA, and to negatively regulate translation of hns by pairing just beyond the translation initiation codon. The class of RNAs that modify activity of proteins is exemplified by CsrB and CsrC of E. coli, two RNAs that bind to and inhibit CsrA, a protein translational regulator. Homologs of CsrA and related regulatory RNAs have been implicated in the regulation of gluconeogenesis, biofilm formation,and virulence factor expression in plant and human pathogens.
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Affiliation(s)
- Nadim Majdalani
- Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892, USA
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Smirnova AV, Ullrich MS. Topological and deletion analysis of CorS, a Pseudomonas syringae sensor kinase. Microbiology (Reading) 2004; 150:2715-2726. [PMID: 15289568 DOI: 10.1099/mic.0.27028-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A modified two-component regulatory system consisting of two response regulators, CorR and CorP, and the histidine protein kinase CorS, regulates the thermoresponsive production of the phytotoxin coronatine (COR) in Pseudomonas syringae PG4180. COR is produced at the virulence-promoting temperature of 18 °C, but not at 28 °C, the optimal growth temperature of PG4180. Assuming that the highly hydrophobic N-terminus of CorS might be involved in temperature-signal perception, the membrane topology of CorS was determined using translational phoA and lacZ fusions, leading to a topological model for CorS with six transmembrane domains (TMDs). Interestingly, three PhoA fusions located downstream of the sixth TMD showed a thermoresponsive phenotype. Enzymic activity, immunoblot, and protease-sensitivity assays were performed to localize the CorS derivatives, to analyse the expression level of hybrid proteins and to examine the model. In-frame deletions of the last four, or all six TMDs gave rise to non-functional CorS. The results indicated that the transmembrane region is important for CorS to function as a temperature sensor, and that the membrane topology of CorS might be involved in signal perception.
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Affiliation(s)
- Angela V Smirnova
- International University Bremen, School of Engineering and Sciences, Research II, Campus Ring 1, 28759 Bremen, Germany
| | - Matthias S Ullrich
- International University Bremen, School of Engineering and Sciences, Research II, Campus Ring 1, 28759 Bremen, Germany
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Hernández-Flores JL, López-López K, Garcidueñas-Piña R, Jofre-Garfias AE, Alvarez-Morales A. The global arginine regulator ArgR controls expression of argF in Pseudomonas syringae pv. phaseolicola but is not required for the synthesis of phaseolotoxin or for the regulated expression of argK. J Bacteriol 2004; 186:3653-5. [PMID: 15150254 PMCID: PMC415750 DOI: 10.1128/jb.186.11.3653-3655.2004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Pseudomonas syringae pv. phaseolicola the enzyme ornithine carbamoyltransferase (OCTase), encoded by argF, is negatively regulated by argR, similar to what has been reported for Pseudomonas aeruginosa. However, production of the phaseolotoxin-resistant OCTase encoded by argK, synthesis of phaseolotoxin, and infectivity for bean pods occur independently of the ArgR protein.
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Affiliation(s)
- José Luis Hernández-Flores
- Departamento de Ingeniería Genética de Plantas, Centro de Investigación y de Estudios Avanzados I.P.N., Unidad Irapuato, Irapuato Gto., CP, México
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17
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Smadja B, Latour X, Trigui S, Burini JF, Chevalier S, Orange N. Thermodependence of growth and enzymatic activities implicated in pathogenicity of two Erwinia carotovora subspecies (Pectobacterium spp.). Can J Microbiol 2004; 50:19-27. [PMID: 15052318 DOI: 10.1139/w03-099] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Erwinia carotovora subsp. atroseptica and Erwinia carotovora subsp. carotovora can cause substantial damage to economically important plant crops and stored products. The occurrence of the disease and the scale of the damage are temperature dependent. Disease development consists first of active multiplication of the bacteria in the infection area and then production of numerous extracellular enzymes. We investigated the effects of various temperatures on these two steps. We assayed the specific growth rate and the pectate lyase and protease activities for eight strains belonging to E. carotovora subsp. atroseptica and E. carotovora subsp. carotovora in vitro. The temperature effect on growth rate and on pectate lyase activity is different for the two subspecies, but protease activity appears to be similarly thermoregulated. Our results are in agreement with ecological data implicating E. carotovora subsp. atroseptica in disease when the temperature is below 20 degrees C. The optimal temperature for pathogenicity appears to be different from the optimal growth temperature but seems to be a compromise between this temperature and temperatures at which lytic activities are maximal.
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Affiliation(s)
- Bruno Smadja
- Laboratoire de Microbiologie du Froid, UPRES 2123, Université de Rouen, Evreux, France
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18
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López-López K, Hernández-Flores JL, Cruz-Aguilar M, Alvarez-Morales A. In Pseudomonas syringae pv. phaseolicola, expression of the argK gene, encoding the phaseolotoxin-resistant ornithine carbamoyltransferase, is regulated indirectly by temperature and directly by a precursor resembling carbamoylphosphate. J Bacteriol 2004; 186:146-53. [PMID: 14679234 PMCID: PMC303443 DOI: 10.1128/jb.186.1.146-153.2004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Accepted: 10/08/2003] [Indexed: 11/20/2022] Open
Abstract
Pseudomonas syringae pv. phaseolicola synthesizes a non-host-specific toxin, phaseolotoxin, and also synthesizes a phaseolotoxin-resistant ornithine carbamoyltransferase (ROCT) to protect itself from its own toxin. ROCT is encoded by argK, which is expressed coordinately with phaseolotoxin synthesis at 18 degrees C. To investigate the regulatory mechanisms of this system, null mutants were constructed for argK, argF (encoding the phaseolotoxin-sensitive OCTase [SOCT]), and amtA (encoding an amidinotransferase involved in phaseolotoxin synthesis). The argF mutant did not exhibit arginine auxotrophy when grown in M9 medium at 28 degrees C, because under this condition SOCT was replaced by ROCT. This loss of thermoregulation of argK was apparently caused by accumulation of carbamoylphosphate, one of the substrates of SOCT. Carbamoylphosphate, which has a structure similar to that of the inorganic moiety of phaseolotoxin, was used in induction assays with wild-type P. syringae pv. phaseolicola and was shown to be able to induce argK expression in M9 medium at 28 degrees C. These results indicate that argK expression is independent of temperature and is regulated directly by a compound resembling the inorganic moiety of phaseolotoxin.
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Affiliation(s)
- Karina López-López
- Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados (CINVESTAV) del Instituto Politecnico Nacional (IPN), Unidad Irapuato, Irapuato, Guanajuato, C.P. 36500, Mexico
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Valverde C, Heeb S, Keel C, Haas D. RsmY, a small regulatory RNA, is required in concert with RsmZ for GacA-dependent expression of biocontrol traits in Pseudomonas fluorescens CHA0. Mol Microbiol 2003; 50:1361-79. [PMID: 14622422 DOI: 10.1046/j.1365-2958.2003.03774.x] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In the plant-beneficial soil bacterium and biocontrol model organism Pseudomonas fluorescens CHA0, the GacS/GacA two-component system upregulates the production of biocontrol factors, i.e. antifungal secondary metabolites and extracellular enzymes, under conditions of slow, non-exponential growth. When activated, the GacS/GacA system promotes the transcription of a small regulatory RNA (RsmZ), which sequesters the small RNA-binding protein RsmA, a translational regulator of genes involved in biocontrol. The gene for a second GacA-regulated small RNA (RsmY) was detected in silico in various pseudomonads, and was cloned from strain CHA0. RsmY, like RsmZ, contains several characteristic GGA motifs. The rsmY gene was expressed in strain CHA0 as a 118 nt transcript which was most abundant in stationary phase, as revealed by Northern blot and transcriptional fusion analysis. Transcription of rsmY was enhanced by the addition of the strain's own supernatant extract containing a quorum-sensing signal and was abolished in gacS or gacA mutants. An rsmA mutation led to reduced rsmY expression, via a gacA-independent mechanism. Overexpression of rsmY restored the expression of target genes (hcnA, aprA) to gacS or gacA mutants. Whereas mutants deleted for either the rsmY or the rsmZ structural gene were not significantly altered in the synthesis of extracellular products (hydrogen cyanide, 2,4-diacetylphloroglucinol, exoprotease), an rsmY rsmZ double mutant was strongly impaired in this production and in its biocontrol properties in a cucumber-Pythium ultimum microcosm. Mobility shift assays demonstrated that multiple molecules of RsmA bound specifically to RsmY and RsmZ RNAs. In conclusion, two small, untranslated RNAs, RsmY and RsmZ, are key factors that relieve RsmA-mediated regulation of secondary metabolism and biocontrol traits in the GacS/GacA cascade of strain CHA0.
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Affiliation(s)
- Claudio Valverde
- Institut de Microbiologie Fondamentale, Bâtiment de Biologie, Université de Lausanne, CH-1015 Lausanne (Dorigny), Switzerland.
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Heeb S, Blumer C, Haas D. Regulatory RNA as mediator in GacA/RsmA-dependent global control of exoproduct formation in Pseudomonas fluorescens CHA0. J Bacteriol 2002; 184:1046-56. [PMID: 11807065 PMCID: PMC134805 DOI: 10.1128/jb.184.4.1046-1056.2002] [Citation(s) in RCA: 295] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In Pseudomonas fluorescens CHA0, an antagonist of root-pathogenic fungi, the GacS/GacA two-component system tightly controls the expression of antifungal secondary metabolites and exoenzymes at a posttranscriptional level, involving the RNA-binding protein and global regulator of secondary metabolism RsmA. This protein was purified from P. fluorescens, and RNA bound to it was converted to cDNA, which served as a probe to isolate the corresponding chromosomal locus, rsmZ. This gene encoded a regulatory RNA of 127 nucleotides and a truncated form lacking 35 nucleotides at the 3' end. Expression of rsmZ depended on GacA, increased with increasing population density, and was stimulated by the addition of a solvent-extractable extracellular signal produced by strain CHA0 at the end of exponential growth. This signal appeared to be unrelated to N-acyl-homoserine lactones. A conserved upstream element in the rsmZ promoter, but not the stress sigma factor RpoS, was involved in rsmZ expression. Overexpression of rsmZ effectively suppressed the negative effect of gacS and gacA mutations on target genes, i.e., hcnA (for hydrogen cyanide synthase) and aprA (for the major exoprotease). Mutational inactivation of rsmZ resulted in reduced expression of these target genes in the presence of added signal. Overexpression of rsmA had a similar, albeit stronger negative effect. These results support a model in which GacA upregulates the expression of regulatory RNAs, such as RsmZ of strain CHA0, in response to a bacterial signal. By a titration effect, RsmZ may then alleviate the repressing activity of RsmA on the expression of target mRNAs.
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Affiliation(s)
- Stephan Heeb
- Laboratoire de Biologie Microbienne, Université de Lausanne, CH-1015 Lausanne, Switzerland
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Ullrich MS, Schergaut M, Boch J, Ullrich B. Temperature-responsive genetic loci in the plant pathogen Pseudomonas syringae pv. glycinea. MICROBIOLOGY (READING, ENGLAND) 2000; 146 ( Pt 10):2457-2468. [PMID: 11021922 DOI: 10.1099/00221287-146-10-2457] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Plant-pathogenic bacteria may sense variations in environmental factors, such as temperature, to adapt to plant-associated habitats during pathogenesis or epiphytic growth. The bacterial blight pathogen of soybean, Pseudomonas syringae pv. glycinea PG4180, preferentially produces the phytotoxin coronatine at 18 degrees C and infects the host plant under conditions of low temperature and high humidity. A miniTn5-based promoterless glucuronidase (uidA) reporter gene was used to identify genetic loci of PG4180 preferentially expressed at 18 or 28 degrees C. Out of 7500 transposon mutants, 61 showed thermoregulated uidA expression as determined by a three-step screening procedure. Two-thirds of these mutants showed an increased reporter gene expression at 18 degrees C whilst the remainder exhibited higher uidA expression at 28 degrees C. MiniTn5-uidA insertion loci from these mutants were subcloned and their nucleotide sequences were determined. Several of the mutants induced at 18 degrees C contained the miniTn5-uidA insertion within the 32.8 kb coronatine biosynthetic gene cluster. Among the other mutants with increased uidA expression at 18 degrees C, insertions were found in genes encoding formaldehyde dehydrogenase, short-chain dehydrogenase and mannuronan C-5-epimerase, in a plasmid-borne replication protein, and in the hrpT locus, involved in pathogenicity of P. syringae. Among the mutants induced at 28 degrees C, insertions disrupted loci with similarities to a repressor of conjugal plasmid transfer, UV resistance determinants, an isoflavanoid-degrading enzyme, a HU-like DNA-binding protein, two additional regulatory proteins, a homologue of bacterial adhesins, transport proteins, LPS synthesis enzymes and two proteases. Genetic loci from 13 mutants did not show significant similarities to any database entries. Results of plant inoculations showed that three of the mutants tested were inhibited in symptom development and in planta multiplication rates. Temperature-shift experiments suggested that all of the identified loci showed a rather slow induction of expression upon change of temperature.
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Affiliation(s)
- Matthias S Ullrich
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, 35043 Marburg, Germany1
| | - Marion Schergaut
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, 35043 Marburg, Germany1
| | - Jens Boch
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, 35043 Marburg, Germany1
| | - Beate Ullrich
- Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Strasse, 35043 Marburg, Germany1
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Rowley KB, Xu R, Patil SS. Molecular analysis of thermoregulation of phaseolotoxin-resistant ornithine carbamoyltransferase (argK) from Pseudomonas syringae pv. phaseolicola. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2000; 13:1071-1080. [PMID: 11043468 DOI: 10.1094/mpmi.2000.13.10.1071] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The phaseolotoxin-resistant ornithine carbamoyltransferase (ROCT) and phaseolotoxin are produced by Pseudomonas syringae pv. phaseolicola at 18 degrees C but not at 28 degrees C. At 28 degrees C, the pathogen produces a protein(s) that binds (in vitro) to a 485-bp fragment (thermoregulatory region, TRR) from a heterologous clone from the pathogen genomic library, which in multiple copies overrides thermoregulation of phaseolotoxin production in wild-type cells (K. B. Rowley, D. E. Clements, M. Mandel, T. Humphreys, and S. S. Patil, Mol. Microbiol. 8:625-635, 1993). We report here that DNase I protection analysis of the 485-bp fragment shows that a single site is protected from cleavage by the protein in the 28 degrees C extract and that this site contains two repeats of a core motif G/C AAAG separated by a 5-bp spacer. Partially purified binding protein forms specific complexes with a synthetic oligonucleotide containing four tandem repeats of this motif. A 492-bp upstream fragment from argK encoding ROCT also forms specific complexes with the protein in the 28 degrees C crude extract, and a 260-bp subfragment from the TRR containing the binding site cross competes with the argk fragment, indicating that the same protein binds to nucleotides in both fragments. DNase I protection analysis of the fragment from argK revealed four separate protected sequence elements, with element III containing half of the core motif sequence (CTTTG), and the other elements containing similar sequences. Gel shift assays were done with DNA fragments from which one or all of the sites were removed as competitor DNAs against the argK probe. The results of these experiments confirmed that the binding sites (in argK) are necessary for the protein to bind to the argK fragment in a specific manner. Taken together, the results of studies presented here suggest that in cells of P. syringae pv. phaseolicola grown at high temperature argK may be negatively regulated by the protein produced at this temperature.
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Affiliation(s)
- K B Rowley
- Biotechnology Program, Pacific Biomedical Research Center, University of Hawaii, Honolulu 96822, USA
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Budde IP, Ullrich MS. Interactions of Pseudomonas syringae pv. glycinea with host and nonhost plants in relation to temperature and phytotoxin synthesis. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2000; 13:951-61. [PMID: 10975652 DOI: 10.1094/mpmi.2000.13.9.951] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Pseudomonas syringae pv. glycinea PG4180 causes bacterial blight of soybean and produces the phytotoxin coronatine (COR) in a temperature-dependent manner. COR consists of a polyketide, coronafacic acid (CFA), and an amino acid derivative, coronamic acid, and is produced optimally at 18 degrees C whereas no detectable synthesis occurs at 28 degrees C. We investigated the impact of temperature on PG4180 during compatible and incompatible interactions with soybean and tobacco plants, respectively. After spray inoculation, PG4180 caused typical bacterial blight symptoms on soybean plants when the bacteria were grown at 18 degrees C prior to inoculation but not when derived from cultures grown at 28 degrees C. The disease outcome was quantified by determination of bacterial populations in planta. The temperature effect was not observed when PG4180 was artificially infiltrated into soybean leaves, indicating that the pre-inoculation temperature and phytotoxin synthesis were important for bacterial invasion via natural plant openings. In the incompatible interaction, PG4180 elicited the hypersensitive response (HR) on tobacco plants regardless of the bacterial pre-inoculation temperature. However, the HR was significantly delayed when tobacco plants were treated with cells of the CFA-overproducing derivative, PG4180.N9, which were derived from cultures grown at 18 degrees C, compared with parallels incubated at 28 degrees C. CFA biosynthesis by PG4180.N9 was optimal at 18 degrees C and negligible at 28 degrees C. The impact of CFA synthesis on the HR was studied with different growth media, mutants, and transconjugants of PG4180, indicating that the amount of synthesized CFA but not that of COR influenced the outcome of the HR. Feeding experiments with purified coronafacoyl compounds suggested that the observed delay of the HR was mediated by CFA, shedding further light on CFA's putative role as a molecular mimic of the plant signaling molecule, jasmonic acid.
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Affiliation(s)
- I P Budde
- Max-Planck-Institut für terrestrische Mikrobiologie, AG Okophysiolgie, Marburg, Germany
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Regeard C, Mérieau A, Leriche F, Guespin-Michel JF. Genetic studies of a thermoregulated gene in the psychrotrophic bacterium Pseudomonas fluorescens. Res Microbiol 1999; 150:447-56. [PMID: 10540908 DOI: 10.1016/s0923-2508(99)00112-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In the psychrotrophic bacterium Pseudomonas fluorescens, some genes are thermoregulated: they are maximally expressed at a particular temperature within the broad range of temperatures that allow growth of this bacterium. To study this regulation, random transcriptional insertion fusions were obtained by means of mini-Tn5lacZ1 or mini-Tn5luxAB transposition. One fusion was studied in which beta-galactosidase production was maximal at a low-growth temperature. The mutated gene (that we call xsf) was highly homologous to xseA from Escherichia coli (and from other bacteria) which encodes the large subunit of exonuclease VII. Genetic tools were constructed in order to analyse and manipulate this fusion: a plasmid derived from R68.45 was used for chromosome transfer and a replacement vector was constructed to allow in situ marker exchange of the mini-Tn5lacZ1 by an Hg(r) interposon. This vector was used to make double mutants and hence to study the effect of the insertion in xsf on the expression of other fusions. Six genes were thereby identified with a decreased expression in an xsf- background and with different characteristics of thermoregulation.
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Affiliation(s)
- C Regeard
- Laboratoire de microbiologie du froid, équipe de génétique et biodiversité, IFR 61 CNRS-Inserm, université de Rouen, faculté des sciences de Rouen, Mt. Saint-Aignan, France
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Bender CL, Alarcón-Chaidez F, Gross DC. Pseudomonas syringae phytotoxins: mode of action, regulation, and biosynthesis by peptide and polyketide synthetases. Microbiol Mol Biol Rev 1999; 63:266-92. [PMID: 10357851 PMCID: PMC98966 DOI: 10.1128/mmbr.63.2.266-292.1999] [Citation(s) in RCA: 516] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Coronatine, syringomycin, syringopeptin, tabtoxin, and phaseolotoxin are the most intensively studied phytotoxins of Pseudomonas syringae, and each contributes significantly to bacterial virulence in plants. Coronatine functions partly as a mimic of methyl jasmonate, a hormone synthesized by plants undergoing biological stress. Syringomycin and syringopeptin form pores in plasma membranes, a process that leads to electrolyte leakage. Tabtoxin and phaseolotoxin are strongly antimicrobial and function by inhibiting glutamine synthetase and ornithine carbamoyltransferase, respectively. Genetic analysis has revealed the mechanisms responsible for toxin biosynthesis. Coronatine biosynthesis requires the cooperation of polyketide and peptide synthetases for the assembly of the coronafacic and coronamic acid moieties, respectively. Tabtoxin is derived from the lysine biosynthetic pathway, whereas syringomycin, syringopeptin, and phaseolotoxin biosynthesis requires peptide synthetases. Activation of phytotoxin synthesis is controlled by diverse environmental factors including plant signal molecules and temperature. Genes involved in the regulation of phytotoxin synthesis have been located within the coronatine and syringomycin gene clusters; however, additional regulatory genes are required for the synthesis of these and other phytotoxins. Global regulatory genes such as gacS modulate phytotoxin production in certain pathovars, indicating the complexity of the regulatory circuits controlling phytotoxin synthesis. The coronatine and syringomycin gene clusters have been intensively characterized and show potential for constructing modified polyketides and peptides. Genetic reprogramming of peptide and polyketide synthetases has been successful, and portions of the coronatine and syringomycin gene clusters could be valuable resources in developing new antimicrobial agents.
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Affiliation(s)
- C L Bender
- Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, Oklahoma 74078-3032, USA.
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Rohde BH, Schmid R, Ullrich MS. Thermoregulated expression and characterization of an NAD(P)H-dependent 2-cyclohexen-1-one reductase in the plant pathogenic bacterium Pseudomonas syringae pv. glycinea. J Bacteriol 1999; 181:814-22. [PMID: 9922244 PMCID: PMC93447 DOI: 10.1128/jb.181.3.814-822.1999] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/1998] [Accepted: 11/24/1998] [Indexed: 11/20/2022] Open
Abstract
The phytopathogenic bacterium Pseudomonas syringae pv. glycinea PG4180.N9 causes bacterial blight of soybeans and preferably infects its host plant during periods of cold, humid weather conditions. To identify proteins differentially expressed at low temperatures, total cellular protein fractions derived from PG4180.N9 grown at 18 and 28 degreesC were separated by two-dimensional gel electrophoresis. Of several proteins which appeared to be preferentially present at 18 degreesC, a 40-kDa protein with an isoelectric point of approximately 5 revealed significant N-terminal sequence homology to morphinone reductase (MR) of Pseudomonas putida M10. The respective P. syringae gene was isolated from a genomic cosmid library of PG4180, and its nucleotide sequence was determined. It was designated ncr for NAD(P)H-dependent 2-cyclohexen-1-one reductase. Comparison of the 1,083-bp open reading frame with database entries revealed 48% identity and 52% similarity to the MR-encoding morB gene of P. putida M10. The ncr gene was overexpressed in Escherichia coli, and its gene product was used to generate polyclonal antisera. Purified recombinant Ncr protein was enzymatically characterized with NAD(P)H and various morphinone analogs as substrates. So far, only 2-cyclohexen-1-one and 3-penten-2-one were found to be substrates for Ncr. By high-pressure liquid chromatography analysis, flavin mononucleotide could be identified as the noncovalently bound prosthetic group of this enzyme. The distribution of the ncr gene in different Pseudomonas species and various strains of P. syringae was analyzed by PCR and Southern blot hybridization. The results indicated that the ncr gene is widespread among P. syringae pv. glycinea strains but not in other pathovars of P. syringae or in any of the other Pseudomonas strains tested.
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Affiliation(s)
- B H Rohde
- AG Okophysiologie, Max-Planck-Institut für terrestrische Mikrobiologie, 35043 Marburg, Germany
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Bender CL, Palmer DA, Peñaloza-Vázquez A, Rangaswamy V, Ullrich M. Biosynthesis and regulation of coronatine, a non-host-specific phytotoxin produced by Pseudomonas syringae. Subcell Biochem 1998; 29:321-41. [PMID: 9594652 DOI: 10.1007/978-1-4899-1707-2_10] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Many P. syringae pathovars are known to produce low-molecular-weight, diffusible toxins in infected host plants. These phytotoxins reproduce some of the symptoms of the relevant bacterial disease and are effective at very low concentrations. Phytotoxins generally enhance the virulence of the P. syringae pathovar which produces them, but are not required for pathogenesis. Genes encoding phytotoxin production have been identified and cloned from several P. syringae pathovars. With the exception of coronatine, toxin biosynthetic gene clusters are generally chromosomally encoded. In several pathovars, the toxin biosynthetic gene cluster also contains a resistance gene which functions to protect the producing strain from the biocidal effects of the toxin. In the case of phaseolotoxin, a resistance gene (argK) has been utilized to engineer phaseolotoxin-resistant tobacco plants. Although P. syringae phytotoxins can induce very similar effects in plants (chlorosis and necrosis), their biosynthesis and mode of action can be quite different. Knowledge of the biosynthetic pathways to these toxins and the cloning of the structural genes for their biosynthesis has relevance to the development of new bioactive compounds with altered specificity. For example, polyketides constitute a huge family of structurally diverse natural products including antibiotics, chemotherapeutic compounds, and antiparasitics. Most of the research on polyketide synthesis in bacteria has focused on compounds synthesized by Streptomyces or other actinomycetes. It is also important to note that it is now possible to utilize a genetic rather than synthetic approach to biosynthesize novel polyketides with altered biological properties (Hutchinson and Fujii, 1995; Kao et al., 1994; Donadio et al., 1993; Katz and Donadio, 1993). Most of the reprogramming or engineering of novel polyketides has been done using actinomycete PKSs, but much of this technology could also be applied to polyketides synthesized by Pseudomonas when sufficient sequence information is available. It is important to note that Pseudomonas produces a variety of antimicrobial compounds from the polyketide pathway, including mupirocin (pseudomonic acid) (Feline et al., 1977), pyoluteorin (Cuppels et al., 1986), and 2-4 diacetylphloroglucinol (Phl) (Bangera and Thomashow, 1996). Pseudomonic acid is valued for its pharmaceutical properties as an antibiotic (Aldridge, 1992), whereas pyoluteorin and Phl have antifungal properties (Howell and Stipanovic, 1980; Keel et al., 1992). A thorough understanding of the biosynthetic pathway to polyketide phytotoxins such as coronatine may ultimately lead to the development of novel compounds with altered biological properties. Thus, specific genes in the biosynthetic pathways of P. syringae phytotoxins could be deployed in other systems to develop new compounds with a wide range of activities.
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Affiliation(s)
- C L Bender
- Department of Plant Pathology, Oklahoma State University, Stillwater 74078-3032, USA
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Zhang YX, Patil SS. The phtE locus in the phaseolotoxin gene cluster has ORFs with homologies to genes encoding amino acid transferases, the AraC family of transcriptional factors, and fatty acid desaturases. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 1997; 10:947-960. [PMID: 9353942 DOI: 10.1094/mpmi.1997.10.8.947] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
A cluster of genes involved in the production of phaseolotoxin, a phytotoxin produced by Pseudomonas syringae pv. phaseolicola, contains eight (phtA through phtH) complementation groups (Y. X. Zhang, K. B. Rowley, and S. S. Patil, J. Bacteriol., 175:6451-6458, 1993). In this study, sequencing of the region encompassing the phtE locus revealed six putative open reading frames (ORFs), each preceded by a putative ribosomal binding site, and all oriented in the same direction. Reverse transcription-polymerase chain reaction suggested that the phtE locus is transcribed as one large (6.4 kb) transcript, indicating that the ORFs constitute an operon. Primer extension analysis showed that the transcript begins at a T, located 31 bp upstream of the ATG codon of ORF1. Comparison of the sequences of the putative ORFs with the sequences of known genes revealed that ORF3, encoding a protein containing 395 amino acids, has 55% similarity to the acetylornithine aminotransferase gene from Escherichia coli, and the ornithine aminotransferase genes from other organisms. A lysine residue that is a binding site for pyridoxal phosphate and an arginine residue that is a binding site for the alpha-carboxylate group of the substrate are conserved in ORF3. These data suggest that ORF3 encodes a protein involved in the biosynthesis of ornithine, a constituent of phaseolotoxin. ORF5, encoding a peptide of 378 amino acid residues, possesses a helix-turn-helix motif at the C-terminal end that is characteristic of the AraC family of transcriptional factors, and there is a possible leucine zipper at the N-terminal end of this peptide. ORF6, encoding a protein of 327 amino acids, has about 40% similarity with the fatty acid desaturase gene, desA, of Synechocystis Pcc6803 and considerable similarity with fatty acid desaturase genes from other organisms. ORF6 and desA show very similar hydropathy profiles and both contain a copper binding signature. Computer searches did not discover significant homologies in the data base for the other ORFs, but hydropathy analysis showed that all of them contain one to several hydrophobic domains, suggesting that the gene products of these ORFs may be membrane associated.
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Affiliation(s)
- Y X Zhang
- Department of Plant Pathology College of Tropical Agriculture and Human Resources, Pacific Biomedical Research Center, University of Hawaii, Honolulu 96822, USA
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Ullrich M, Peñaloza-Vázquez A, Bailey AM, Bender CL. A modified two-component regulatory system is involved in temperature-dependent biosynthesis of the Pseudomonas syringae phytotoxin coronatine. J Bacteriol 1995; 177:6160-9. [PMID: 7592381 PMCID: PMC177456 DOI: 10.1128/jb.177.21.6160-6169.1995] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Biosynthesis of the phytotoxin coronatine (COR) in Pseudomonas syringae pv. glycinea PG4180 is regulated by temperature at the transcriptional level. A 3.4-kb DNA fragment from the COR biosynthetic gene cluster restored temperature-regulated phytotoxin production to Tn5 mutants defective in COR production. Nucleotide sequence analysis of this fragment revealed three genes, corS, corP, and corR, which encode a modified two-component regulatory system consisting of one sensor protein, CorS, and two response regulator proteins, CorP and CorR. Although only one response regulator, CorR, had a DNA-binding domain, the phosphate-receiving domains of both response regulator proteins were highly conserved. Transcriptional fusions of the corP and corR promoters to a promoterless glucuronidase gene (uidA) indicated that these two genes are expressed constitutively at 18 and 28 degrees C. In contrast, a corS::uidA fusion exhibited the temperature dependence previously observed for COR biosynthetic promoters and exhibited maximal transcriptional activity at 18 degrees C and low activity at 28 degrees C. Furthermore, glucuronidase activity for corS::uidA was decreased in corP, corR, and corS mutants relative to the levels observed for PG4180(corS::uidA). This difference was not observed for corP::uidA and corR::uidA transcriptional fusions since expression of these fusions remained low and constitutive regardless of the genetic background. The three regulatory genes functioned in a P. syringae strain lacking the COR gene cluster to achieve temperature-dependent activation of an introduced COR biosynthetic promoter, indicating that this triad of genes is the primary control for COR biosynthesis and responsible for thermoregulation. Our data suggest that the modified two-component regulatory system described in this study might transduce and amplify a temperature signal which results in transcriptional activation of COR biosynthetic genes.
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Affiliation(s)
- M Ullrich
- Department of Plant Pathology, Oklahoma State University, Stillwater 74078-3032, USA
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Zhang Y, Rowley KB, Patil SS. Genetic organization of a cluster of genes involved in the production of phaseolotoxin, a toxin produced by Pseudomonas syringae pv. phaseolicola. J Bacteriol 1993; 175:6451-8. [PMID: 8407821 PMCID: PMC206753 DOI: 10.1128/jb.175.20.6451-6458.1993] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Phaseolotoxin [N delta(N'-sulfo-diaminophosphinyl)-ornithyl-alanyl- homoarginine] produced by Pseudomonas syringae pv. phaseolicola, the bean halo blight pathogen, is a potent inhibitor of ornithine carbamoyltransferase (OCT). Inhibition of OCT in infected plants leads to chlorosis and growth inhibition. A genomic cosmid clone, pHK120, containing a 25-kb fragment of DNA from a wild-type strain of P. syringae pv. phaseolicola restores toxin production in Tox- mutants. Tn5 mutagenesis of pHK120 and marker exchange of pHK120::Tn5 plasmids in the wild-type strain resulted in the isolation of 39 chromosomal mutants that harbor Tn5 insertions at known positions. Toxin bioassays revealed that 28 of the mutants, with Tn5 insertions distributed throughout the insert of pHK120, were Tox-, indicating that a functional locus for toxin production in each mutant was inactivated. Complementation analysis was done by testing for toxin production strains that carried a genomic Tn5 at one location and a plasmid-borne Tn5 at another location (pair complementation). Pair complementation analysis of nine marker exchange mutants and a random genomic Tn5 mutant revealed that there are a minimum of eight toxin loci (phtA through phtH) in pHK120. Mutants carrying Tn5 insertions in the phtA, phtD, and phtF loci were complemented by deletion subclones containing fragments from pHK120; mutants carrying Tn5 insertions in the phtC locus were partially complemented by a subclone, and mutants carrying Tn5 insertions in the phtB, phtE, phtG, and phtH loci were not complemented by any of the available subclones. A comparison of the insert from pHK120 with that from pRCP17, a clone reported previously (R. C. Peet, P. B. Lindgren, D. K. Wills, and N. J. Panopoulos, J. Bacteriol. 166:1096-1105, 1986) by another laboratory to contain some of the phaseolotoxin genes and the phaseolotoxin-resistant OCT gene, revealed that the inserts in these two cosmids overlap but differ in important respects.
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Affiliation(s)
- Y Zhang
- Department of Plant Pathology, University of Hawaii, Honolulu 96822
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