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Two pathways act in an additive rather than obligatorily synergistic fashion to induce systemic acquired resistance and PR gene expression.

Zhang C, Shapiro AD - BMC Plant Biol. (2002)

Bottom Line: Two pathways act additively, rather than in an obligatorily synergistic fashion, to induce systemic acquired resistance, PR-1 and PR-5.One of these pathways is NPR1-independent and depends on signals associated with hypersensitive cell death.At least two other pathways also contribute additively to PR-5 induction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Plant and Soil Sciences, Delaware Agricultural Experiment Station, College of Agriculture and Natural Resources, University of Delaware, Newark, DE, USA. zhangchu@udel.edu

ABSTRACT

Background: Local infection with necrotizing pathogens induces whole plant immunity to secondary challenge. Pathogenesis-related genes are induced in parallel with this systemic acquired resistance response and thought to be co-regulated. The hypothesis of co-regulation has been challenged by induction of Arabidopsis PR-1 but not systemic acquired resistance in npr1 mutant plants responding to Pseudomonas syringae carrying the avirulence gene avrRpt2. However, experiments with ndr1 mutant plants have revealed major differences between avirulence genes. The ndr1-1 mutation prevents hypersensitive cell death, systemic acquired resistance and PR-1 induction elicited by bacteria carrying avrRpt2. This mutation does not prevent these responses to bacteria carrying avrB.

Results: Systemic acquired resistance, PR-1 induction and PR-5 induction were assessed in comparisons of npr1-2 and ndr1-1 mutant plants, double mutant plants, and wild-type plants. Systemic acquired resistance was displayed by all four plant lines in response to Pseudomonas syringae bacteria carrying avrB. PR-1 induction was partially impaired by either single mutation in response to either bacterial strain, but only fully impaired in the double mutant in response to avrRpt2. PR-5 induction was not fully impaired in any of the mutants in response to either avirulence gene.

Conclusion: Two pathways act additively, rather than in an obligatorily synergistic fashion, to induce systemic acquired resistance, PR-1 and PR-5. One of these pathways is NPR1-independent and depends on signals associated with hypersensitive cell death. The other pathway is dependent on salicylic acid accumulation and acts through NPR1. At least two other pathways also contribute additively to PR-5 induction.

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Boolean representation of signaling network The binary switches used to represent allele status at the NPR1 and NDR1 loci were rendered according to standard depictions in engineering texts. All other symbols are according to Genoud, Trevino Santa Cruz and Métraux [24]. Signal generators were rendered as rectangles with black boxes inside them set at one or zero. "Or" gates, indicating that either input is sufficient to give the specified output, were rendered as bullet shapes with concave left sides. "And" gates, indicating that both inputs are required to give the specified output, were rendered as bullet shapes with flat left sides. Signaling outputs that also serve as inputs to downstream events were rendered as open triangles. Branches in the pathway were indicated with filled circles to suggest the resemblance to contact points in electrical circuit diagrams.
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Figure 4: Boolean representation of signaling network The binary switches used to represent allele status at the NPR1 and NDR1 loci were rendered according to standard depictions in engineering texts. All other symbols are according to Genoud, Trevino Santa Cruz and Métraux [24]. Signal generators were rendered as rectangles with black boxes inside them set at one or zero. "Or" gates, indicating that either input is sufficient to give the specified output, were rendered as bullet shapes with concave left sides. "And" gates, indicating that both inputs are required to give the specified output, were rendered as bullet shapes with flat left sides. Signaling outputs that also serve as inputs to downstream events were rendered as open triangles. Branches in the pathway were indicated with filled circles to suggest the resemblance to contact points in electrical circuit diagrams.

Mentions: These details are presented in a model of the signaling network for induction of SAR, PR-1 gene expression and PR-5 gene expression by avirulent P. syringae bacteria (Figure 4). We have used a representation scheme proposed recently for plant signal transduction networks that is based on Boolean formalisms used in engineering and computer science [24]. Either of two "generators" shown can elicit signaling. One generator is infection of plants carrying a functional RPS2 allele with bacteria carrying avrRpt2. The second generator is infection of plants carrying a functional RPM1 allele with bacteria carrying avrB. An "or" gate is used to show that either way of eliciting signaling resulted in accumulation of SA. The NDR1 allele status was represented with a "switch". The ndr1-1 allele was pictured as analogous to an electrical switch where the contact is in an open position, impairing early SA accumulation.


Two pathways act in an additive rather than obligatorily synergistic fashion to induce systemic acquired resistance and PR gene expression.

Zhang C, Shapiro AD - BMC Plant Biol. (2002)

Boolean representation of signaling network The binary switches used to represent allele status at the NPR1 and NDR1 loci were rendered according to standard depictions in engineering texts. All other symbols are according to Genoud, Trevino Santa Cruz and Métraux [24]. Signal generators were rendered as rectangles with black boxes inside them set at one or zero. "Or" gates, indicating that either input is sufficient to give the specified output, were rendered as bullet shapes with concave left sides. "And" gates, indicating that both inputs are required to give the specified output, were rendered as bullet shapes with flat left sides. Signaling outputs that also serve as inputs to downstream events were rendered as open triangles. Branches in the pathway were indicated with filled circles to suggest the resemblance to contact points in electrical circuit diagrams.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC130961&req=5

Figure 4: Boolean representation of signaling network The binary switches used to represent allele status at the NPR1 and NDR1 loci were rendered according to standard depictions in engineering texts. All other symbols are according to Genoud, Trevino Santa Cruz and Métraux [24]. Signal generators were rendered as rectangles with black boxes inside them set at one or zero. "Or" gates, indicating that either input is sufficient to give the specified output, were rendered as bullet shapes with concave left sides. "And" gates, indicating that both inputs are required to give the specified output, were rendered as bullet shapes with flat left sides. Signaling outputs that also serve as inputs to downstream events were rendered as open triangles. Branches in the pathway were indicated with filled circles to suggest the resemblance to contact points in electrical circuit diagrams.
Mentions: These details are presented in a model of the signaling network for induction of SAR, PR-1 gene expression and PR-5 gene expression by avirulent P. syringae bacteria (Figure 4). We have used a representation scheme proposed recently for plant signal transduction networks that is based on Boolean formalisms used in engineering and computer science [24]. Either of two "generators" shown can elicit signaling. One generator is infection of plants carrying a functional RPS2 allele with bacteria carrying avrRpt2. The second generator is infection of plants carrying a functional RPM1 allele with bacteria carrying avrB. An "or" gate is used to show that either way of eliciting signaling resulted in accumulation of SA. The NDR1 allele status was represented with a "switch". The ndr1-1 allele was pictured as analogous to an electrical switch where the contact is in an open position, impairing early SA accumulation.

Bottom Line: Two pathways act additively, rather than in an obligatorily synergistic fashion, to induce systemic acquired resistance, PR-1 and PR-5.One of these pathways is NPR1-independent and depends on signals associated with hypersensitive cell death.At least two other pathways also contribute additively to PR-5 induction.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Plant and Soil Sciences, Delaware Agricultural Experiment Station, College of Agriculture and Natural Resources, University of Delaware, Newark, DE, USA. zhangchu@udel.edu

ABSTRACT

Background: Local infection with necrotizing pathogens induces whole plant immunity to secondary challenge. Pathogenesis-related genes are induced in parallel with this systemic acquired resistance response and thought to be co-regulated. The hypothesis of co-regulation has been challenged by induction of Arabidopsis PR-1 but not systemic acquired resistance in npr1 mutant plants responding to Pseudomonas syringae carrying the avirulence gene avrRpt2. However, experiments with ndr1 mutant plants have revealed major differences between avirulence genes. The ndr1-1 mutation prevents hypersensitive cell death, systemic acquired resistance and PR-1 induction elicited by bacteria carrying avrRpt2. This mutation does not prevent these responses to bacteria carrying avrB.

Results: Systemic acquired resistance, PR-1 induction and PR-5 induction were assessed in comparisons of npr1-2 and ndr1-1 mutant plants, double mutant plants, and wild-type plants. Systemic acquired resistance was displayed by all four plant lines in response to Pseudomonas syringae bacteria carrying avrB. PR-1 induction was partially impaired by either single mutation in response to either bacterial strain, but only fully impaired in the double mutant in response to avrRpt2. PR-5 induction was not fully impaired in any of the mutants in response to either avirulence gene.

Conclusion: Two pathways act additively, rather than in an obligatorily synergistic fashion, to induce systemic acquired resistance, PR-1 and PR-5. One of these pathways is NPR1-independent and depends on signals associated with hypersensitive cell death. The other pathway is dependent on salicylic acid accumulation and acts through NPR1. At least two other pathways also contribute additively to PR-5 induction.

Show MeSH
Related in: MedlinePlus