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Richard A Sikora - One of the best experts on this subject based on the ideXlab platform.
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effectiveness of systemic resistance toward aphis gossypii hom aphididae as induced by combined applications of the endophytes fusarium oxysporum fo162 and Rhizobium etli g12
Biological Control, 2012Co-Authors: Alfonso Martinuz, Alexander Schouten, R D Menjivar, Richard A SikoraAbstract:Abstract The mutualistic root-colonizing endophytes Fusarium oxysporum strain Fo162 (Fo162) and Rhizobium etli strain G12 (G12) have been shown to individually induce systemic resistance against the sucking insect Aphis gossypii Glover (Hom., Aphididae). Simultaneous application of both organisms may be a strategy to further increase the systemic defense responses and thus the biocontrol efficacy. The simultaneous inoculation of both endophytes, either in a mixed or in a spatially-separated way, also reduced the aphid population in comparison to untreated squash plants. However, both types of combined treatments did not lead to significant additive biocontrol levels, i.e. further reduction in the aphid population, when compared to individual inoculation. A choice experiment with intact squash plants showed that the aphids favor feeding on endophyte-free plants, indicating that both Fo162 and G12 are able to affect the host plant preference by the aphids. The data illustrate that cocktail type inoculants comprising of different beneficial microorganisms may not always enhance the biocontrol efficacy against insects. Thus, although both Fo162 and G12 are recognized as biocontrol agents, their mutual interactions and their interactions with the host plant have to be taken into account in co-inoculation strategies in biocontrol.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:ABSTRACT Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematodeGlobodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction betweenRhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml−1. Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction ofG. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heatstable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml 21 . Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots. Antagonistic rhizobacteria have been repeatedly shown to be promising microorganisms for the biological control of plant-parasitic nematodes. In a screening program, 16 bacterial isolates out of 179 isolated from root and cysts caused a significant (.25%) reduction in Globodera pallida penetration of potato roots (27). A 68% reduction of sugar beet cyst nematode root invasion was obtained by application of the rhizobacterium Pseudomonas fluorescens P523 to beet seeds (23). Studies on a number of plant-microbe interactions showed that such antagonistic rhizobacteria can function directly by competition and antibiosis (3) but also indirectly by inducing systemic resistance in the plant toward soil-borne pathogens (9, 17, 36). However, bacterial compounds which induce plant defense mechanisms are highly variable. Enhanced defense by Pseudomonas aeruginosa strain 7NSK2 in bean toward the pathogenic fungus Botrytis cinerea was initiated by bacterial salicylic acid (5). The siderophore pyoverdin of P. fluorescens strain CHAO was involved in systemically induced suppression of tobacco necrosis virus in tobacco (8). In tomato and soybean leaves, lipopolysaccharides (LPS) of incompatible pseudomonads induced resistance against challenge inoculations by compatible bacteria (20). Induced systemic resistance in carnation to Fusarium wilt was triggered by heat-killed cells and purified LPS, extracted from the outer membrane of P. fluorescens strain WCS417r (36). Previous work demonstrated that living and heat-killed cells of Rhizobium etli G12 induced in potato roots systemic resistance against G. pallida infection (9, 11). The results of these studies suggested that heat-stable surface structures of R. etli G12 may be the inducing factors. Surface carbohydrates of Rhizobium consist mainly of exopolysaccharides (EPS) as additional capsular or slimy layers around the bacterial cell and LPS, which are an integral part of the outer membrane of the cell. Surface carbohydrates play an important role during the recognition process in the symbiotic interaction between Rhizobium and legumes (6, 16). Furthermore, some authors proposed that degradation of rhizobial polysaccharides is involved in the regulation of the plant response (19). The objective of this investigation was to extract EPS and LPS from the rhizobacterium R. etli G12 and to determine whether these carbohydrates act as inducers of systemic resistance in potato roots to G. pallida infection.
M Reitz - One of the best experts on this subject based on the ideXlab platform.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:ABSTRACT Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematodeGlobodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction betweenRhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml−1. Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction ofG. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heatstable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml 21 . Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots. Antagonistic rhizobacteria have been repeatedly shown to be promising microorganisms for the biological control of plant-parasitic nematodes. In a screening program, 16 bacterial isolates out of 179 isolated from root and cysts caused a significant (.25%) reduction in Globodera pallida penetration of potato roots (27). A 68% reduction of sugar beet cyst nematode root invasion was obtained by application of the rhizobacterium Pseudomonas fluorescens P523 to beet seeds (23). Studies on a number of plant-microbe interactions showed that such antagonistic rhizobacteria can function directly by competition and antibiosis (3) but also indirectly by inducing systemic resistance in the plant toward soil-borne pathogens (9, 17, 36). However, bacterial compounds which induce plant defense mechanisms are highly variable. Enhanced defense by Pseudomonas aeruginosa strain 7NSK2 in bean toward the pathogenic fungus Botrytis cinerea was initiated by bacterial salicylic acid (5). The siderophore pyoverdin of P. fluorescens strain CHAO was involved in systemically induced suppression of tobacco necrosis virus in tobacco (8). In tomato and soybean leaves, lipopolysaccharides (LPS) of incompatible pseudomonads induced resistance against challenge inoculations by compatible bacteria (20). Induced systemic resistance in carnation to Fusarium wilt was triggered by heat-killed cells and purified LPS, extracted from the outer membrane of P. fluorescens strain WCS417r (36). Previous work demonstrated that living and heat-killed cells of Rhizobium etli G12 induced in potato roots systemic resistance against G. pallida infection (9, 11). The results of these studies suggested that heat-stable surface structures of R. etli G12 may be the inducing factors. Surface carbohydrates of Rhizobium consist mainly of exopolysaccharides (EPS) as additional capsular or slimy layers around the bacterial cell and LPS, which are an integral part of the outer membrane of the cell. Surface carbohydrates play an important role during the recognition process in the symbiotic interaction between Rhizobium and legumes (6, 16). Furthermore, some authors proposed that degradation of rhizobial polysaccharides is involved in the regulation of the plant response (19). The objective of this investigation was to extract EPS and LPS from the rhizobacterium R. etli G12 and to determine whether these carbohydrates act as inducers of systemic resistance in potato roots to G. pallida infection.
Paul V Attwood - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of Inhibition of Rhizobium etli Pyruvate Carboxylase by L‑Aspartate
2016Co-Authors: Chaiyos Sirithanakorn, Sarawut Jitrapakdee, John C. Wallace, Abdussalam Adina-zada, Paul V AttwoodAbstract:ABSTRACT: L-Aspartate is a regulatory feedback inhibitor of the biotin-dependent enzyme pyruvate carboxylase in response to increased levels of tricarboxylic acid cycle intermediates. Detailed studies of L-aspartate inhibition of pyruvate carboxylase have been mainly confined to eukaryotic microbial enzymes, and aspects of its mode of action remain unclear. Here we examine its inhibition of the bacterial enzyme Rhizobium etli pyruvate carboxylase. Kinetic studies demonstrated that L-aspartate binds to the enzyme cooperatively and inhibits the enzyme competitively with respect to acetyl-CoA. L-Aspartate also inhibits activation of the enzyme by MgTNP-ATP. The action of L-aspartate was not confined to inhibition of acetyl-CoA binding, because the acetyl-CoA-independent activity of the enzyme was also inhibited by increasing concentrations of L-aspartate. This inhibition of acetyl-CoA-independent activity was demonstrated to be focused in the biotin carboxylation domain of the enzyme, and it had no effect on the oxamate-induced oxaloacetate decarboxylation reaction that occurs in the carboxyl transferase domain. L-Aspartate was shown to competitively inhibit bicarbonate-dependent MgATP cleavage with respect to MgATP but also probably inhibits carboxybiotin formation and/or translocation of the carboxybiotin to the site of pyruvate carboxylation. Unlike acetyl-CoA, L-aspartate has no effect on the coupling between MgATP cleavage and oxaloacetate formation
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investigation of the roles of allosteric domain arginine aspartate and glutamate residues of Rhizobium etli pyruvate carboxylase in relation to its activation by acetyl coa
Biochemistry, 2016Co-Authors: Chaiyos Sirithanakorn, Sarawut Jitrapakdee, Paul V AttwoodAbstract:The mechanism of allosteric activation of pyruvate carboxylase by acetyl CoA is not fully understood. Here we have examined the roles of residues near the acetyl CoA binding site in the allosteric activation of Rhizobium etli pyruvate carboxylase using site-directed mutagenesis. Arg429 was found to be especially important for acetyl CoA binding as substitution with serine resulted in a 100-fold increase in the Ka of acetyl CoA activation and a large decrease in the cooperativity of this activation. Asp420 and Arg424, which do not make direct contact with bound acetyl CoA, were nonetheless found to affect acetyl CoA binding when mutated, probably through changed interactions with another acetyl CoA binding residue, Arg427. Thermodynamic activation parameters for the pyruvate carboxylation reaction were determined from modified Arrhenius plots and showed that acetyl CoA acts to decrease the activation free energy of the reaction by both increasing the activation entropy and decreasing the activation enthalp...
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Interaction between the biotin carboxyl carrier domain and the biotin carboxylase domain in pyruvate carboxylase from Rhizobium etli.
Biochemistry, 2011Co-Authors: A.d. Lietzan, Paul V Attwood, Ann L. Menefee, Tonya N. Zeczycki, Sudhanshu Kumar, John C. Wallace, W. Wallace Cleland, Martin St. MauriceAbstract:Pyruvate carboxylase (PC) catalyzes the ATP-dependent carboxylation of pyruvate to oxaloacetate, an important anaplerotic reaction in mammalian tissues. To effect catalysis, the tethered biotin of PC must gain access to active sites in both the biotin carboxylase domain and the carboxyl transferase domain. Previous studies have demonstrated that a mutation of threonine 882 to alanine in PC from Rhizobium etli renders the carboxyl transferase domain inactive and favors the positioning of biotin in the biotin carboxylase domain. We report the 2.4 A resolution X-ray crystal structure of the Rhizobium etli PC T882A mutant which reveals the first high-resolution description of the domain interaction between the biotin carboxyl carrier protein domain and the biotin carboxylase domain. The overall quaternary arrangement of Rhizobium etli PC remains highly asymmetrical and is independent of the presence of allosteric activator. While biotin is observed in the biotin carboxylase domain, its access to the active site is precluded by the interaction between Arg353 and Glu248, revealing a mechanism for regulating carboxybiotin access to the BC domain active site. The binding location for the biotin carboxyl carrier protein domain demonstrates that tethered biotin cannot bind in the biotin carboxylase domain active site in the same orientation as free biotin, helping to explain the difference in catalysis observed between tethered biotin and free biotin substrates in biotin carboxylase enzymes. Electron density located in the biotin carboxylase domain active site is assigned to phosphonoacetate, offering a probable location for the putative carboxyphosphate intermediate formed during biotin carboxylation. The insights gained from the T882A Rhizobium etli PC crystal structure provide a new series of catalytic snapshots in PC and offer a revised perspective on catalysis in the biotin-dependent enzyme family.
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insight into the carboxyl transferase domain mechanism of pyruvate carboxylase from Rhizobium etli
Biochemistry, 2009Co-Authors: Tonya N. Zeczycki, Sarawut Jitrapakdee, Paul V Attwood, John C. Wallace, Martin St. Maurice, W. Wallace ClelandAbstract:The effects of mutations in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase have been determined for the forward reaction to form oxaloacetate, the reverse reaction to form MgATP, the oxamate-induced decarboxylation of oxaloacetate, the phosphorylation of MgADP by carbamoyl phosphate, and the bicarbonate-dependent ATPase reaction. Additional studies with these mutants examined the effect of pyruvate and oxamate on the reactions of the biotin carboxylase domain. From these mutagenic studies, putative roles for catalytically relevant active site residues were assigned and a more accurate description of the mechanism of the carboxyl transferase domain is presented. The T882A mutant showed no catalytic activity for reactions involving the carboxyl transferase domain but surprisingly showed 7- and 3.5-fold increases in activity, as compared to that of the wild-type enzyme, for the ADP phosphorylation and bicarbonate-dependent ATPase reactions, respectively. Furthermore...
Klaus Rudolph - One of the best experts on this subject based on the ideXlab platform.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:ABSTRACT Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematodeGlobodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction betweenRhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml−1. Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction ofG. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heatstable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml 21 . Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots. Antagonistic rhizobacteria have been repeatedly shown to be promising microorganisms for the biological control of plant-parasitic nematodes. In a screening program, 16 bacterial isolates out of 179 isolated from root and cysts caused a significant (.25%) reduction in Globodera pallida penetration of potato roots (27). A 68% reduction of sugar beet cyst nematode root invasion was obtained by application of the rhizobacterium Pseudomonas fluorescens P523 to beet seeds (23). Studies on a number of plant-microbe interactions showed that such antagonistic rhizobacteria can function directly by competition and antibiosis (3) but also indirectly by inducing systemic resistance in the plant toward soil-borne pathogens (9, 17, 36). However, bacterial compounds which induce plant defense mechanisms are highly variable. Enhanced defense by Pseudomonas aeruginosa strain 7NSK2 in bean toward the pathogenic fungus Botrytis cinerea was initiated by bacterial salicylic acid (5). The siderophore pyoverdin of P. fluorescens strain CHAO was involved in systemically induced suppression of tobacco necrosis virus in tobacco (8). In tomato and soybean leaves, lipopolysaccharides (LPS) of incompatible pseudomonads induced resistance against challenge inoculations by compatible bacteria (20). Induced systemic resistance in carnation to Fusarium wilt was triggered by heat-killed cells and purified LPS, extracted from the outer membrane of P. fluorescens strain WCS417r (36). Previous work demonstrated that living and heat-killed cells of Rhizobium etli G12 induced in potato roots systemic resistance against G. pallida infection (9, 11). The results of these studies suggested that heat-stable surface structures of R. etli G12 may be the inducing factors. Surface carbohydrates of Rhizobium consist mainly of exopolysaccharides (EPS) as additional capsular or slimy layers around the bacterial cell and LPS, which are an integral part of the outer membrane of the cell. Surface carbohydrates play an important role during the recognition process in the symbiotic interaction between Rhizobium and legumes (6, 16). Furthermore, some authors proposed that degradation of rhizobial polysaccharides is involved in the regulation of the plant response (19). The objective of this investigation was to extract EPS and LPS from the rhizobacterium R. etli G12 and to determine whether these carbohydrates act as inducers of systemic resistance in potato roots to G. pallida infection.
I Schroder - One of the best experts on this subject based on the ideXlab platform.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:ABSTRACT Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematodeGlobodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heat-stable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction betweenRhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml−1. Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction ofG. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots.
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lipopolysaccharides of Rhizobium etli strain g12 act in potato roots as an inducing agent of systemic resistance to infection by the cyst nematode globodera pallida
Applied and Environmental Microbiology, 2000Co-Authors: M Reitz, Klaus Rudolph, I Schroder, S Hoffmannhergarten, Johannes Hallmann, Richard A SikoraAbstract:Recent studies have shown that living and heat-killed cells of the rhizobacterium Rhizobium etli strain G12 induce in potato roots systemic resistance to infection by the potato cyst nematode Globodera pallida. To better understand the mechanisms of induced resistance, we focused on identifying the inducing agent. Since heatstable bacterial surface carbohydrates such as exopolysaccharides (EPS) and lipopolysaccharides (LPS) are essential for recognition in the symbiotic interaction between Rhizobium and legumes, their role in the R. etli-potato interaction was studied. EPS and LPS were extracted from bacterial cultures, applied to potato roots, and tested for activity as an inducer of plant resistance to the plant-parasitic nematode. Whereas EPS did not affect G. pallida infection, LPS reduced nematode infection significantly in concentrations as low as 1 and 0.1 mg ml 21 . Split-root experiments, guaranteeing a spatial separation of inducing agent and challenging pathogen, showed that soil treatments of one half of the root system with LPS resulted in a highly significant (up to 37%) systemic induced reduction of G. pallida infection of potato roots in the other half. The results clearly showed that LPS of R. etli G12 act as the inducing agent of systemic resistance in potato roots. Antagonistic rhizobacteria have been repeatedly shown to be promising microorganisms for the biological control of plant-parasitic nematodes. In a screening program, 16 bacterial isolates out of 179 isolated from root and cysts caused a significant (.25%) reduction in Globodera pallida penetration of potato roots (27). A 68% reduction of sugar beet cyst nematode root invasion was obtained by application of the rhizobacterium Pseudomonas fluorescens P523 to beet seeds (23). Studies on a number of plant-microbe interactions showed that such antagonistic rhizobacteria can function directly by competition and antibiosis (3) but also indirectly by inducing systemic resistance in the plant toward soil-borne pathogens (9, 17, 36). However, bacterial compounds which induce plant defense mechanisms are highly variable. Enhanced defense by Pseudomonas aeruginosa strain 7NSK2 in bean toward the pathogenic fungus Botrytis cinerea was initiated by bacterial salicylic acid (5). The siderophore pyoverdin of P. fluorescens strain CHAO was involved in systemically induced suppression of tobacco necrosis virus in tobacco (8). In tomato and soybean leaves, lipopolysaccharides (LPS) of incompatible pseudomonads induced resistance against challenge inoculations by compatible bacteria (20). Induced systemic resistance in carnation to Fusarium wilt was triggered by heat-killed cells and purified LPS, extracted from the outer membrane of P. fluorescens strain WCS417r (36). Previous work demonstrated that living and heat-killed cells of Rhizobium etli G12 induced in potato roots systemic resistance against G. pallida infection (9, 11). The results of these studies suggested that heat-stable surface structures of R. etli G12 may be the inducing factors. Surface carbohydrates of Rhizobium consist mainly of exopolysaccharides (EPS) as additional capsular or slimy layers around the bacterial cell and LPS, which are an integral part of the outer membrane of the cell. Surface carbohydrates play an important role during the recognition process in the symbiotic interaction between Rhizobium and legumes (6, 16). Furthermore, some authors proposed that degradation of rhizobial polysaccharides is involved in the regulation of the plant response (19). The objective of this investigation was to extract EPS and LPS from the rhizobacterium R. etli G12 and to determine whether these carbohydrates act as inducers of systemic resistance in potato roots to G. pallida infection.