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Christoph Keel - One of the best experts on this subject based on the ideXlab platform.
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combination of fluorescent reporters for simultaneous monitoring of Root colonization and antifungal gene expression by a biocontrol pseudomonad on cereals with flow cytometry
Molecular Plant-microbe Interactions, 2010Co-Authors: Laurene Rochat, Maria Pechytarr, Eric Baehler, Monika Maurhofer, Christoph KeelAbstract:Some Root-associated pseudomonads sustain plant growth by suppressing Root Diseases caused by pathogenic fungi. We investigated to which extent select cereal cultivars influence expression of relevant biocontrol traits (i.e., Root colonization efficacy and antifungal activity) in Pseudomonas fluorescens CHA0. In this representative plant-beneficial bacterium, the antifungal metabolites 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin (PRN), pyoluteorin (PLT), and hydrogen cyanide (HCN) are required for biocontrol. To monitor host plant effects on the expression of biosynthetic genes for these compounds on Roots, we developed fluorescent dual-color reporters suited for flow cytometric analysis using fluorescence-activated cell sorting (FACS). In the dual-label strains, the constitutively expressed red fluorescent protein mCherry served as a cell tag and marker for Root colonization, whereas reporter fusions based on the green fluorescent protein allowed simultaneous recording of antifungal gene expression w...
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combination of fluorescent reporters for simultaneous monitoring of Root colonization and antifungal gene expression by a biocontrol pseudomonad on cereals with flow cytometry
Molecular Plant-microbe Interactions, 2010Co-Authors: Laurene Rochat, Maria Pechytarr, Eric Baehler, Monika Maurhofer, Christoph KeelAbstract:Some Root-associated pseudomonads sustain plant growth by suppressing Root Diseases caused by pathogenic fungi. We investigated to which extent select cereal cultivars influence expression of relevant biocontrol traits (i.e., Root colonization efficacy and antifungal activity) in Pseudomonas fluorescens CHA0. In this representative plant-beneficial bacterium, the antifungal metabolites 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin (PRN), pyoluteorin (PLT), and hydrogen cyanide (HCN) are required for biocontrol. To monitor host plant effects on the expression of biosynthetic genes for these compounds on Roots, we developed fluorescent dual-color reporters suited for flow cytometric analysis using fluorescence-activated cell sorting (FACS). In the dual-label strains, the constitutively expressed red fluorescent protein mCherry served as a cell tag and marker for Root colonization, whereas reporter fusions based on the green fluorescent protein allowed simultaneous recording of antifungal gene expression within the same cell. FACS analysis revealed that expression of DAPG and PRN biosynthetic genes was promoted in a cereal rhizosphere, whereas expression of PLT and HCN biosynthetic genes was markedly less sustained. When analyzing the response of the bacterial reporters on Roots of a selection of wheat, spelt, and triticale cultivars, we were able to detect subtle species- and cultivar-dependent differences in colonization and DAPG and HCN gene expression levels. The expression of these biocontrol traits was particularly favored on Roots of one spelt cultivar, suggesting that a careful choice of pseudomonad-cereal combinations might be beneficial to biocontrol. Our approach may be useful for selective single-cell level analysis of plant effects in other bacteria-Root interactions.
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Molecular analysis of a novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas fluorescens.
Environmental microbiology, 2008Co-Authors: Maria Péchy-tarr, Monika Maurhofer, Joyce E. Loper, Marcella D. Henkels, Denny J. Bruck, Esther Fischer, Christelle Vogne, Kelly M. Donahue, Jürg Grunder, Christoph KeelAbstract:Pseudomonas fluorescens CHA0 and the related strain Pf-5 are well-characterized representatives of rhizosphere bacteria that have the capacity to protect crop plants from fungal Root Diseases, mainly by releasing a variety of exoproducts that are toxic to plant pathogenic fungi. Here, we report that the two plant-beneficial pseudomonads also exhibit potent insecticidal activity. Anti-insect activity is linked to a novel genomic locus encoding a large protein toxin termed Fit (for P. fluorescensinsecticidal toxin) that is related to the insect toxin Mcf (Makes caterpillars floppy) of the entomopathogen Photorhabdus luminescens, a mutualist of insect-invading nematodes. When injected into the haemocoel, even low doses of P. fluorescens CHA0 or Pf-5 killed larvae of the tobacco hornworm Manduca sexta and the greater wax moth Galleria mellonella. In contrast, mutants of CHA0 or Pf-5 with deletions in the Fit toxin gene were significantly less virulent to the larvae. When expressed from an inducible promoter in a non-toxic Escherichia coli host, the Fit toxin gene was sufficient to render the bacterium toxic to both insect hosts. Our findings establish the Fit gene products of P. fluorescens CHA0 and Pf-5 as potent insect toxins that define previously unappreciated anti-insect properties of these plant-colonizing bacteria.
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the sigma factor algu algt controls exopolysaccharide production and tolerance towards desiccation and osmotic stress in the biocontrol agent pseudomonas fluorescens cha0
Applied and Environmental Microbiology, 2001Co-Authors: Ursula Schniderkeel, Eric Baehler, Dieter Haas, Kirsten Bang Lejbolle, Christoph KeelAbstract:A variety of stress situations may affect the activity and survival of plant-beneficial pseudomonads added to soil to control Root Diseases. This study focused on the roles of the sigma factor AlgU (synonyms, AlgT, RpoE, and sigma(22)) and the anti-sigma factor MucA in stress adaptation of the biocontrol agent Pseudomonas fluorescens CHA0. The algU-mucA-mucB gene cluster of strain CHA0 was similar to that of the pathogens Pseudomonas aeruginosa and Pseudomonas syringae. Strain CHA0 is naturally nonmucoid, whereas a mucA deletion mutant or algU-overexpressing strains were highly mucoid due to exopolysaccharide overproduction. Mucoidy strictly depended on the global regulator GacA. An algU deletion mutant was significantly more sensitive to osmotic stress than the wild-type CHA0 strain and the mucA mutant were. Expression of an algU'-'lacZ reporter fusion was induced severalfold in the wild type and in the mucA mutant upon exposure to osmotic stress, whereas a lower, noninducible level of expression was observed in the algU mutant. Overexpression of algU did not enhance tolerance towards osmotic stress. AlgU was found to be essential for tolerance of P. fluorescens towards desiccation stress in a sterile vermiculite-sand mixture and in a natural sandy loam soil. The size of the population of the algU mutant declined much more rapidly than the size of the wild-type population at soil water contents below 5%. In contrast to its role in pathogenic pseudomonads, AlgU did not contribute to tolerance of P. fluorescens towards oxidative and heat stress. In conclusion, AlgU is a crucial determinant in the adaptation of P. fluorescens to dry conditions and hyperosmolarity, two major stress factors that limit bacterial survival in the environment.
David M Weller - One of the best experts on this subject based on the ideXlab platform.
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construction of a proteome reference map and response of gaeumannomyces graminis var tritici to 2 4 diacetylphloroglucinol
Fungal Biology, 2018Co-Authors: Young Sang Kwon, Linda S Thomashow, David M Weller, Changwook Jeon, Younsig KwakAbstract:Abstract Take-all disease, caused by Gaeumannomyces graminis var. tritici (Ggt), is one of the most serious Root Diseases in wheat production. In this study, a proteomic platform based on 2-dimensional gel electrophoresis (2-DE) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Tandem Mass Spectrometry (MALDI-TOF/TOF MS) was used to construct the first proteome database reference map of G. graminis var. tritici and to identify the response of the pathogen to 2,4-diacetylphloroglucinol (DAPG), which is a natural antibiotic produced by antagonistic Pseudomonas spp. in take-all suppressive soils. For mapping, a total of 240 spots was identified that represented 209 different proteins. The most abundant biological function categories in the Ggt proteome were related to carbohydrate metabolism (21%), amino acid metabolism (15%), protein folding and degradation (12%), translation (11%), and stress response (10%). In total, 51 Ggt proteins were affected by DAPG treatment. Based on gene ontology, carbohydrate metabolism, amino acid metabolism, stress response, and protein folding and degradation proteins were the ones most modulated by DAPG treatment. This study provides the first extensive proteomic reference map constructed for Ggt and represents the first time that the response of Ggt to DAPG has been characterized at the proteomic level.
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biological control of wheat Root Diseases by the clp producing strain pseudomonas fluorescens hc1 07
Phytopathology, 2014Co-Authors: Mingming Yang, Linda S Thomashow, Shanshan Wen, Dmitri V Mavrodi, Olga V Mavrodi, Diter Von Wettstein, Jianhua Guo, David M WellerAbstract:Pseudomonas fluorescens HC1-07, previously isolated from the phyllosphere of wheat grown in Hebei province, China, suppresses the soilborne disease of wheat take-all, caused by Gaeumannomyces graminis var. tritici. We report here that strain HC1-07 also suppresses Rhizoctonia Root rot of wheat caused by Rhizoctonia solani AG-8. Strain HC1-07 produced a cyclic lipopeptide (CLP) with a molecular weight of 1,126.42 based on analysis by electrospray ionization mass spectrometry. Extracted CLP inhibited the growth of G. graminis var. tritici and R. solani in vitro. To determine the role of this CLP in biological control, plasposon mutagenesis was used to generate two nonproducing mutants, HC1-07viscB and HC1-07prtR2. Analysis of regions flanking plasposon insertions in HC1-07prtR2 and HC1-07viscB revealed that the inactivated genes were similar to prtR and viscB, respectively, of the well-described biocontrol strain P. fluorescens SBW25 that produces the CLP viscosin. Both genes in HC1-07 were required for the production of the viscosin-like CLP. The two mutants were less inhibitory to G. graminis var. tritici and R. solani in vitro and reduced in ability to suppress take-all. HC1-07viscB but not HC-07prtR2 was reduced in ability to suppress Rhizoctonia Root rot. In addition to CLP production, prtR also played a role in protease production.
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yield responses of direct seeded wheat to rhizobacteria and fungicide seed treatments
Plant Disease, 2002Co-Authors: James R Cook, David M Weller, Dan Vakoch, Adel Youssef Elbanna, Hao ZhangAbstract:Cook, R. J., Weller, D. M., Youssef El-Banna, A., Vakoch, D., and Zhang, H. 2002. Yield responses of direct-seeded wheat to rhizobacteria and fungicide seed treatments. Plant Dis. 86:780-784. Field trials were conducted with winter and spring wheat in eastern Washington and northern Idaho over several years to determine the benefit, as measured by grain yield, of seed treatments with rhizobacteria and formulated fungicides in cropping systems favorable to Root Diseases. The trials were conducted with wheat direct-seeded (no-till) in fields with a history of intensive cereals and one or more of the Root Diseases: take-all caused by Gaeumannomyces graminis var. tritici, Rhizoctonia Root rot caused by Rhizoctonia solani AG8 and R. oryzae, and Pythium Root rot caused mainly by Pythium irregulare and P. ultimum. The seed treatments included Bacillus sp. L324-92, Pseudomonas fluorescens Q69c-80, Pseudomonas fluorescens Q8r1-96, difenoconazole + metalaxyl (Dividend + Apron), difenoconazole + mefenoxam (Dividend + Apron XL = Dividend XL), tebuconazole + metalaxyl (Raxil XT), and tebuconazole + thiram (Raxil-thiram). Controls were nontreated seed planted into both nontreated (natural) soil and soil fumigated with methyl bromide just prior to planting. Although the data indicate a trend in higher wheat yields with two rhizobacteria treatments over the nontreated control (171 and 264 kg/ha, respectively), these higher yields were not significantly different from the nontreated control (P = 0.06). Fungicide seed treatments alone similarly resulted in yields that were 100 to 300 kg/ha higher than the nontreated control, but only the yield responses to Dividend on winter wheat (289 kg/ha) and Dividend + Apron on spring wheat (263 kg/ha) were significant (P ≤ 0.05). The greatest yield increases over the nontreated control occurred with certain rhizobacteria–fungicide combinations, with three treatments in the range of 312 to 486 kg/ha (6.1 to 17.7%; P ≤ 0.05). Some rhizobacteria–fungicide combinations brought average yields to within 85 to 90% of those obtained with soil fumigation. Only soil fumigation produced a measurable reduction in the incidence of take-all and Rhizoctonia Root rot, as assessed on washed Roots. No reliable method exists for visual quantification of Pythium Root rot on wheat.
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a rapid polymerase chain reaction based assay characterizing rhizosphere populations of 2 4 diacetylphloroglucinol producing bacteria
Phytopathology, 2001Co-Authors: B Mc Spadden B Gardener, Linda S Thomashow, Dmitri V Mavrodi, David M WellerAbstract:ABSTRACT Pseudomonas species that produce 2,4-diacetylphloroglucinol (2,4-DAPG) play a significant role in the suppression of fungal Root pathogens in the rhizosphere of crop plants. To characterize the abundance and diversity of these functionally important bacterial populations, we developed a rapid polymerase chain reaction (PCR)-based assay targeting phlD, an essential gene in the phloroglucinol biosynthetic pathway. The phlDgene is predicted to encode a polyketide synthase that synthesizes mono-acetylphloroglucinol, the immediate precursor to 2,4-DAPG. A major portion of the phlD open reading frame was cloned and sequenced from five genotypically distinct strains, and the sequences were screened for conserved regions that could be used as gene-specific priming sites for PCR amplification. Several new phlD-specific primers were designed and evaluated. Using the primers B2BF and BPR4, we developed a PCR-based assay that was robust enough to amplify the target gene from a diverse set of 2,4-DAPG producers and sensitive enough to detect as few as log 2.4 cells per sample when combined with enrichment from a selective medium. Restriction fragment length polymorphism analysis of the amplified phlD sequence allows for the direct determination of the genotype of the most abundant 2,4-DAPG producers in a sample. The method described was useful for characterizing both inoculant and indigenous phlD(+) pseudomonads inhabiting the rhizosphere of crop plants. The ability to rapidly characterize populations of 2,4-DAPG-producers will greatly enhance our understanding of their role in the suppression of Root Diseases.
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bacillus sp l324 92 for biological control of three Root Diseases of wheat grown with reduced tillage
Phytopathology, 1997Co-Authors: Dalsoo Kim, James R Cook, David M WellerAbstract:ABSTRACT Strain L324-92 is a novel Bacillus sp. with biological activity against three Root Diseases of wheat, namely take-all caused by Gaeumannomyces graminis var. tritici, Rhizoctonia Root rot caused by Rhizoctonia solani AG8, and Pythium Root rot caused mainly by Pythium irregulare and P. ultimum, that exhibits broad-spectrum inhibitory activity and grows at temperatures from 4 to 40°C. These three Root Diseases are major yieldlimiting factors for wheat in the U.S. Inland Pacific Northwest, especially wheat direct-drilled into the residue of a previous cereal crop. Strain L324-92 was selected from among approximately 2,000 rhizosphere/rhizoplane isolates of Bacillus species isolated from Roots of wheat collected from two eastern Washington wheat fields that had long histories of wheat. Roots were washed, heat-treated (80°C for 30 min), macerated, and dilution-plated on 1/10-strength tryptic soy agar. Strain L324-92 inhibited all isolates of G. graminis var. tritici, Rhizoctonia species and anastomosis...
Monika Maurhofer - One of the best experts on this subject based on the ideXlab platform.
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combination of fluorescent reporters for simultaneous monitoring of Root colonization and antifungal gene expression by a biocontrol pseudomonad on cereals with flow cytometry
Molecular Plant-microbe Interactions, 2010Co-Authors: Laurene Rochat, Maria Pechytarr, Eric Baehler, Monika Maurhofer, Christoph KeelAbstract:Some Root-associated pseudomonads sustain plant growth by suppressing Root Diseases caused by pathogenic fungi. We investigated to which extent select cereal cultivars influence expression of relevant biocontrol traits (i.e., Root colonization efficacy and antifungal activity) in Pseudomonas fluorescens CHA0. In this representative plant-beneficial bacterium, the antifungal metabolites 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin (PRN), pyoluteorin (PLT), and hydrogen cyanide (HCN) are required for biocontrol. To monitor host plant effects on the expression of biosynthetic genes for these compounds on Roots, we developed fluorescent dual-color reporters suited for flow cytometric analysis using fluorescence-activated cell sorting (FACS). In the dual-label strains, the constitutively expressed red fluorescent protein mCherry served as a cell tag and marker for Root colonization, whereas reporter fusions based on the green fluorescent protein allowed simultaneous recording of antifungal gene expression w...
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combination of fluorescent reporters for simultaneous monitoring of Root colonization and antifungal gene expression by a biocontrol pseudomonad on cereals with flow cytometry
Molecular Plant-microbe Interactions, 2010Co-Authors: Laurene Rochat, Maria Pechytarr, Eric Baehler, Monika Maurhofer, Christoph KeelAbstract:Some Root-associated pseudomonads sustain plant growth by suppressing Root Diseases caused by pathogenic fungi. We investigated to which extent select cereal cultivars influence expression of relevant biocontrol traits (i.e., Root colonization efficacy and antifungal activity) in Pseudomonas fluorescens CHA0. In this representative plant-beneficial bacterium, the antifungal metabolites 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin (PRN), pyoluteorin (PLT), and hydrogen cyanide (HCN) are required for biocontrol. To monitor host plant effects on the expression of biosynthetic genes for these compounds on Roots, we developed fluorescent dual-color reporters suited for flow cytometric analysis using fluorescence-activated cell sorting (FACS). In the dual-label strains, the constitutively expressed red fluorescent protein mCherry served as a cell tag and marker for Root colonization, whereas reporter fusions based on the green fluorescent protein allowed simultaneous recording of antifungal gene expression within the same cell. FACS analysis revealed that expression of DAPG and PRN biosynthetic genes was promoted in a cereal rhizosphere, whereas expression of PLT and HCN biosynthetic genes was markedly less sustained. When analyzing the response of the bacterial reporters on Roots of a selection of wheat, spelt, and triticale cultivars, we were able to detect subtle species- and cultivar-dependent differences in colonization and DAPG and HCN gene expression levels. The expression of these biocontrol traits was particularly favored on Roots of one spelt cultivar, suggesting that a careful choice of pseudomonad-cereal combinations might be beneficial to biocontrol. Our approach may be useful for selective single-cell level analysis of plant effects in other bacteria-Root interactions.
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role of gluconic acid production in the regulation of biocontrol traits of pseudomonas fluorescens cha0
Applied and Environmental Microbiology, 2009Co-Authors: Patrice De Werra, Maria Pechytarr, C Keel, Monika MaurhoferAbstract:The rhizobacterium Pseudomonas fluorescens CHA0 promotes the growth of various crop plants and protects them against Root Diseases caused by pathogenic fungi. The main mechanism of disease suppression by this strain is the production of the antifungal compounds 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT). Direct plant growth promotion can be achieved through solubilization of inorganic phosphates by the production of organic acids, mainly gluconic acid, which is one of the principal acids produced by Pseudomonas spp. The aim of this study was to elucidate the role of gluconic acid production in CHA0. Therefore, mutants were created with deletions in the genes encoding glucose dehydrogenase (gcd) and gluconate dehydrogenase (gad), required for the conversion of glucose to gluconic acid and gluconic acid to 2-ketogluconate, respectively. These enzymes should be of predominant importance for rhizosphere-colonizing biocontrol bacteria, as major carbon sources provided by plant Root exudates are made up of glucose. Our results show that the ability of strain CHA0 to acidify its environment and to solubilize mineral phosphate is strongly dependent on its ability to produce gluconic acid. Moreover, we provide evidence that the formation of gluconic acid by CHA0 completely inhibits the production of PLT and partially inhibits that of DAPG. In the Δgcd mutant, which does not produce gluconic acid, the enhanced production of antifungal compounds was associated with improved biocontrol activity against take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici. This study provides new evidence for a close association of gluconic acid metabolism with antifungal compound production and biocontrol activity in P. fluorescens CHA0.
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Molecular analysis of a novel gene cluster encoding an insect toxin in plant-associated strains of Pseudomonas fluorescens.
Environmental microbiology, 2008Co-Authors: Maria Péchy-tarr, Monika Maurhofer, Joyce E. Loper, Marcella D. Henkels, Denny J. Bruck, Esther Fischer, Christelle Vogne, Kelly M. Donahue, Jürg Grunder, Christoph KeelAbstract:Pseudomonas fluorescens CHA0 and the related strain Pf-5 are well-characterized representatives of rhizosphere bacteria that have the capacity to protect crop plants from fungal Root Diseases, mainly by releasing a variety of exoproducts that are toxic to plant pathogenic fungi. Here, we report that the two plant-beneficial pseudomonads also exhibit potent insecticidal activity. Anti-insect activity is linked to a novel genomic locus encoding a large protein toxin termed Fit (for P. fluorescensinsecticidal toxin) that is related to the insect toxin Mcf (Makes caterpillars floppy) of the entomopathogen Photorhabdus luminescens, a mutualist of insect-invading nematodes. When injected into the haemocoel, even low doses of P. fluorescens CHA0 or Pf-5 killed larvae of the tobacco hornworm Manduca sexta and the greater wax moth Galleria mellonella. In contrast, mutants of CHA0 or Pf-5 with deletions in the Fit toxin gene were significantly less virulent to the larvae. When expressed from an inducible promoter in a non-toxic Escherichia coli host, the Fit toxin gene was sufficient to render the bacterium toxic to both insect hosts. Our findings establish the Fit gene products of P. fluorescens CHA0 and Pf-5 as potent insect toxins that define previously unappreciated anti-insect properties of these plant-colonizing bacteria.
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suppression of Root Diseases by pseudomonas fluorescens cha0 importance of the bacterial secondary metabolite 2 4 diacetylphloroglucinol
Molecular Plant-microbe Interactions, 1992Co-Authors: C Keel, Monika Maurhofer, Ursula Schnider, Christophe Voisard, Jacques Laville, Ulrich Burger, P Wirthner, Dieter Haas, Genevieve DefagoAbstract:Pseudomonas fluorescens strain CHAO suppresses Thielaviopsis basicola-induced black Root rot of tobacco and Gaeumannomyces graminis var. tritici-induced take-all of wheat. Strain CHAO produces 2,4-diacetylphloroglucinol, a metabolite with antifungal, antibacterial, and phytotoxic activity. The role of this compound in disease suppression was tested under gnotobiotic conditions. A P. fluorescens mutant, obtained by Tn5 insertion, did not produce 2,4-diacetylphloroglucinol, showed diminished inhibition of T. basicola and of G. g. var. tritici in vitro, and had a reduced suppressive effect on tobacco black Root rot and on take-all of wheat, compared with wild-type CHAO. Complementation of the mutant with an 11-kb DNA fragment from a genomic library of wild-type CHAO largely restored production of the metabolite, inhibition of the fungal pathogens in vitro and disease suppression. The Tn5 insertion was physically mapped using a 5.8-kb complementing fragment as a probe. 2,4- Diacetylphloroglucinol was shown to be produced in the rhizosphere of wheat by strain CHAO and by the complemented mutant, but not by the mutant defective in 2,4-diacetylphloroglucinol synthesis. These results support the importance of 2,4-diacetylphloroglucinol production by strain CHAO in the suppression of soilborne plant pathogens in the rhizosphere.
Linda S Thomashow - One of the best experts on this subject based on the ideXlab platform.
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construction of a proteome reference map and response of gaeumannomyces graminis var tritici to 2 4 diacetylphloroglucinol
Fungal Biology, 2018Co-Authors: Young Sang Kwon, Linda S Thomashow, David M Weller, Changwook Jeon, Younsig KwakAbstract:Abstract Take-all disease, caused by Gaeumannomyces graminis var. tritici (Ggt), is one of the most serious Root Diseases in wheat production. In this study, a proteomic platform based on 2-dimensional gel electrophoresis (2-DE) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Tandem Mass Spectrometry (MALDI-TOF/TOF MS) was used to construct the first proteome database reference map of G. graminis var. tritici and to identify the response of the pathogen to 2,4-diacetylphloroglucinol (DAPG), which is a natural antibiotic produced by antagonistic Pseudomonas spp. in take-all suppressive soils. For mapping, a total of 240 spots was identified that represented 209 different proteins. The most abundant biological function categories in the Ggt proteome were related to carbohydrate metabolism (21%), amino acid metabolism (15%), protein folding and degradation (12%), translation (11%), and stress response (10%). In total, 51 Ggt proteins were affected by DAPG treatment. Based on gene ontology, carbohydrate metabolism, amino acid metabolism, stress response, and protein folding and degradation proteins were the ones most modulated by DAPG treatment. This study provides the first extensive proteomic reference map constructed for Ggt and represents the first time that the response of Ggt to DAPG has been characterized at the proteomic level.
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biological control of wheat Root Diseases by the clp producing strain pseudomonas fluorescens hc1 07
Phytopathology, 2014Co-Authors: Mingming Yang, Linda S Thomashow, Shanshan Wen, Dmitri V Mavrodi, Olga V Mavrodi, Diter Von Wettstein, Jianhua Guo, David M WellerAbstract:Pseudomonas fluorescens HC1-07, previously isolated from the phyllosphere of wheat grown in Hebei province, China, suppresses the soilborne disease of wheat take-all, caused by Gaeumannomyces graminis var. tritici. We report here that strain HC1-07 also suppresses Rhizoctonia Root rot of wheat caused by Rhizoctonia solani AG-8. Strain HC1-07 produced a cyclic lipopeptide (CLP) with a molecular weight of 1,126.42 based on analysis by electrospray ionization mass spectrometry. Extracted CLP inhibited the growth of G. graminis var. tritici and R. solani in vitro. To determine the role of this CLP in biological control, plasposon mutagenesis was used to generate two nonproducing mutants, HC1-07viscB and HC1-07prtR2. Analysis of regions flanking plasposon insertions in HC1-07prtR2 and HC1-07viscB revealed that the inactivated genes were similar to prtR and viscB, respectively, of the well-described biocontrol strain P. fluorescens SBW25 that produces the CLP viscosin. Both genes in HC1-07 were required for the production of the viscosin-like CLP. The two mutants were less inhibitory to G. graminis var. tritici and R. solani in vitro and reduced in ability to suppress take-all. HC1-07viscB but not HC-07prtR2 was reduced in ability to suppress Rhizoctonia Root rot. In addition to CLP production, prtR also played a role in protease production.
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a rapid polymerase chain reaction based assay characterizing rhizosphere populations of 2 4 diacetylphloroglucinol producing bacteria
Phytopathology, 2001Co-Authors: B Mc Spadden B Gardener, Linda S Thomashow, Dmitri V Mavrodi, David M WellerAbstract:ABSTRACT Pseudomonas species that produce 2,4-diacetylphloroglucinol (2,4-DAPG) play a significant role in the suppression of fungal Root pathogens in the rhizosphere of crop plants. To characterize the abundance and diversity of these functionally important bacterial populations, we developed a rapid polymerase chain reaction (PCR)-based assay targeting phlD, an essential gene in the phloroglucinol biosynthetic pathway. The phlDgene is predicted to encode a polyketide synthase that synthesizes mono-acetylphloroglucinol, the immediate precursor to 2,4-DAPG. A major portion of the phlD open reading frame was cloned and sequenced from five genotypically distinct strains, and the sequences were screened for conserved regions that could be used as gene-specific priming sites for PCR amplification. Several new phlD-specific primers were designed and evaluated. Using the primers B2BF and BPR4, we developed a PCR-based assay that was robust enough to amplify the target gene from a diverse set of 2,4-DAPG producers and sensitive enough to detect as few as log 2.4 cells per sample when combined with enrichment from a selective medium. Restriction fragment length polymorphism analysis of the amplified phlD sequence allows for the direct determination of the genotype of the most abundant 2,4-DAPG producers in a sample. The method described was useful for characterizing both inoculant and indigenous phlD(+) pseudomonads inhabiting the rhizosphere of crop plants. The ability to rapidly characterize populations of 2,4-DAPG-producers will greatly enhance our understanding of their role in the suppression of Root Diseases.
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molecular mechanisms of defense by rhizobacteria against Root disease
Proceedings of the National Academy of Sciences of the United States of America, 1995Co-Authors: Richard J Cook, Linda S Thomashow, David M Weller, D K Fujimoto, M Mazzola, Gita Mahalaxmi BangeraAbstract:Abstract Genetic resistance in plants to Root Diseases is rare, and agriculture depends instead on practices such as crop rotation and soil fumigation to control these Diseases. "Induced suppression" is a natural phenomenon whereby a soil due to microbiological changes converts from conducive to suppressive to a soilborne pathogen during prolonged monoculture of the susceptible host. Our studies have focused on the wheat Root disease "take-all," caused by the fungus Gaeumannomyces graminis var. tritici, and the role of bacteria in the wheat rhizosphere (rhizobacteria) in a well-documented induced suppression (take-all decline) that occurs in response to the disease and continued monoculture of wheat. The results summarized herein show that antibiotic production plays a significant role in both plant defense by and ecological competence of rhizobacteria. Production of phenazine and phloroglucinol antibiotics, as examples, account for most of the natural defense provided by fluorescent Pseudomonas strains isolated from among the diversity of rhizobacteria associated with take-all decline. There appear to be at least three levels of regulation of genes for antibiotic biosynthesis: environmental sensing, global regulation that ties antibiotic production to cellular metabolism, and regulatory loci linked to genes for pathway enzymes. Plant defense by rhizobacteria producing antibiotics on Roots and as cohabitants with pathogens in infected tissues is analogous to defense by the plant's production of phytoalexins, even to the extent that an enzyme of the same chalcone/stilbene synthase family used to produce phytoalexins is used to produce 2,4-diacetylphloroglucinol. The defense strategy favored by selection pressure imposed on plants by soilborne pathogens may well be the ability of plants to support and respond to rhizosphere microorganisms antagonistic to these pathogens.
John Scullion - One of the best experts on this subject based on the ideXlab platform.
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introduced earthworms in agricultural and reclaimed land their ecology and influences on soil properties plant production and other soil biota
Biological Invasions, 2006Co-Authors: G H Baker, G Brown, Kevin R Butt, J P Curry, John ScullionAbstract:Accidental and deliberate introductions of earthworms into agricultural and reclaimed land are natural experiments that provide opportunities to understand the attributes of successful invaders and their impacts on local biota and ecosystem processes. We consider various case studies (e.g., earthworm invasions in agricultural soils in Australia and Brazil) and deliberate introductions of earthworms into reclaimed mine sites, landfills and cutaway peat in the U.K. and Ireland. Invasions of exotic earthworms, such as European Lumbricidae in Australia, have been geographically extensive, but remain very patchy at regional and field scales. Their impacts on soil properties, plant production and other biota are therefore also likely to be patchy. Various methods have been developed to deliberately inoculate exotic earthworms into disturbed lands, with varying degrees of success. The factors controlling success are, in general, poorly understood. A broad range of impacts of invasive earthworms on soil properties (e.g., soil structure, nutrient availability, burial of surface materials, incidence of Root Diseases) and plant yield and quality have been reported. Less is known of the impacts of invasive earthworms on other soil fauna, but they are likely to occur due to alterations in food availability and habitat structure. Influences on other biota are likely to extend to aboveground communities as well as those belowground. Introductions of earthworms to disturbed lands can yield substantial benefits in agricultural productivity and amelioration of soil degradation. However, the potential impact of the promotion or control of such introductions on non-target biota and ecosystem processes in pristine ecosystems nearby should be considered.
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introduced earthworms in agricultural and reclaimed land their ecology and influences on soil properties plant production and other soil biota
Biological Invasions, 2006Co-Authors: G H Baker, Kevin R Butt, J P Curry, George G Brown, John ScullionAbstract:Accidental and deliberate introductions of earthworms into agricultural and reclaimed land are natural experiments that provide opportunities to understand the attributes of successful invaders and their impacts on local biota and ecosystem processes. We consider various case studies (e.g., earthworm invasions in agricultural soils in Australia and Brazil) and deliberate introductions of earthworms into reclaimed mine sites, landfills and cutaway peat in the U.K. and Ireland. Invasions of exotic earthworms, such as European Lumbricidae in Australia, have been geographically extensive, but remain very patchy at regional and field scales. Their impacts on soil properties, plant production and other biota are therefore also likely to be patchy. Various methods have been developed to deliberately inoculate exotic earthworms into disturbed lands, with varying degrees of success. The factors controlling success are, in general, poorly understood. A broad range of impacts of invasive earthworms on soil properties (e.g., soil structure, nutrient availability, burial of surface materials, incidence of Root Diseases) and plant yield and quality have been reported. Less is known of the impacts of invasive earthworms on other soil fauna, but they are likely to occur due to alterations in food availability and habitat structure. Influences on other biota are likely to extend to aboveground communities as well as those belowground. Introductions of earthworms to disturbed lands can yield substantial benefits in agricultural productivity and amelioration of soil degradation. However, the potential impact of the promotion or control of such introductions on non-target biota and ecosystem processes in pristine ecosystems nearby should be considered.
