Plant Innate Immunity (eBook)

Front Cover 1
Advances in Botanical Research 4
Copyright Page 5
Contents 6
Contributors to Volume 51 12
Preface: Plant Innate Immunity 16
Contents of Volumes 35–50 20
Chapter 1: PAMP-Triggered Basal Immunity in Plants 34
I. The Concept of Plant Immunity 35
II. Signals Mediating the Activation of Plant Defense Responses 37
A. Pathogen-Associated Molecular Patterns 37
B. Damage-Associated Molecular Patterns 44
C. Pathogen-Derived Toxins as Triggers of Plant Immunity 45
III. Receptors Mediating Pattern Recognition in Plant Immunity 48
IV. Signal Transduction in PTI 54
V. Suppression of PTI—A Major Virulence Strategy of Phytopathogenic Bacteria 58
VI. Concluding Remarks 60
Acknowledgments 61
References 61
Chapter 2: Plant Pathogens as Suppressors of Host Defense 72
I. Introduction 73
II. Suppressors Produced by Fungal and Oomycete Pathogens 75
A. Suppressors Comprise a Wide Group of Metabolites 75
B. Race-Specific Elicitors Turn Out to Suppress Defenses 77
C. Concluding Remarks 81
III. Suppressors Produced by Bacterial Pathogens 81
A. Bacterial Evolution to Overcome Plant Resistance 81
B. Bacterial Suppression of PTI 83
1. Calcium signaling suppression by extracellular polysaccharides (EPS) 84
2. Coronatine toxin suppression of stomatal closure 85
C. Type III Protein Secreted Effectors are Used to Suppress PTI 85
D. Multifunctional Effectors 86
1. avrPto 86
2. avrPtoB (hopAB2) 87
3. avrRpt2 88
4. xopD 89
E. RNA and RNA-Binding Protein Targeting 89
1. hopU1 (hopPtoS2) 89
2. hopT1-1 90
F. Attack of Negative Regulators of PTI 90
1. avrB 90
2. avrRpm1 91
G. Targeting Hormone Signaling? 91
1. hopAN (avrE1/wtsE/dspA/dspE) 91
2. hopAM1 (avrPpiB) 92
H. Disruption of Vesicle Trafficking 92
1. hopM1 (hopPtoM) 92
I. Targeting MAP Kinase Signaling 94
1. HopAI1 94
J. Other Effectors Involved in PTI Suppression for Which Targets are Unknown 94
1. avrRps4 94
2. hopAO1 (hopPtoD2) 95
K. Other Effectors Involved in PTI Suppression, but Lacking Functional Information 95
L. Other Potential Mechanisms—Type VI Secretion 96
M. Complexity and Evolution of PTI Suppression by Bacterial Pathogens 96
IV. RNA Silencing, the Plant's Innate Immune System Against Viruses 98
A. The Discovery of RNA Silencing as the Plant’s Innate Immune System Against Viruses 98
B. Current Views of RNA Silencing as Antiviral Mechanism in 99
1. The siRNA pathway 100
2. The miRNA pathway 102
C. Viral Suppressors of RNA Silencing 102
D. Possible Interactions Between Plant Viruses and the miRNA Pathway 105
E. Is Antiviral RNAi Restricted to Plants and Insects? 106
Acknowledgments 107
References 107
Chapter 3: From Nonhost Resistance to Lesion-Mimic Mutants: Useful for Studies of Defense Signaling 124
I. Introduction 125
II. Defense Induction Mediated by PAMPs and Effectors 126
III. Signaling Downstream of Pathogen Detection 129
A. The SA-Signaling Pathway 130
IV. Commonalities in the Defense Response of Host and Nonhost Resistance 132
A. Penetration Resistance of Arabidopsis 133
B. Nonhost Resistance to Bacteria 136
V. What is the Explanation for Nonhost Resistance? 137
VI. Lesion-Mimic Mutants 140
VII. Mutant Screens Without Pathogens for Finding Genes in Defense Signaling 141
A. SSD Mutants 141
B. SFD Mutants 143
C. MOS Mutants 144
VIII. Conclusion 145
Acknowledgments 145
References 145
Chapter 4: Action at a Distance: Long-Distance Signals in Induced Resistance 156
I. Introduction 157
II. Time to Flower—Signaling Events in the Vegetative to Flowering Transition 158
A. Flowering Time as a Model for Long-Distance Signaling 158
B. Control of Flowering Occurs in Distinct Stages 158
C. The Long-Distance Flowering Signal is Phloem Mobile and Highly Conserved 159
D. Candidates for the Floral Long-Distance SignalmdashThe Identity of "Florigen" 160
1. Sucrose, cytokinins, and gibberellins 160
2. Characterization of genes involved in the regulation of flowering time 161
3. FT protein is phloem-mobile 162
4. FT, a near universal flowering signal: ‘‘florigen’’ revealed 163
E. Salicylic Acid and FloweringmdashConvergence of Signaling Mechanisms? 164
III. Mechanisms of Signaling During the Wound Response 165
A. Role of Systemin in Systemic Wound Signaling 166
B. Wound-Response Mutants are Deficient in the Biosynthesis or Perception of JA, or in Systemin Functioning 167
C. Systemin and JA Production in Wounded Leaves and JA Perception in Distant Tissue 168
D. JA Biosynthesis Occurs in the Sieve Element/Companion Cell Complex 169
E. JA-Mediated Wound Response is Modulated by Other Signals 170
F. Mechanism of JA Action on Effector Genes 171
IV. Long-Distance Signaling in SAR 171
A. SAR Develops in Distinct Stages 172
1. Induction 172
2. Movement of a long-distance signal(s) 173
3. Establishment of the ‘‘primed’’ plant 173
4. Manifestation 174
B. Role of SA and NPR1 in SAR 174
C. SAR Signal Transport 175
D. Candidates for the SAR Long-Distance Signal 176
E. Other Genes Involved in SAR Long-Distance Signaling 179
F. Role of ET in SAR Long-Distance Signaling 182
G. SAR Long-Distance Signaling Across Species 182
V. Systemic Induced Susceptibility (SIS) 183
VI. Signaling During ISR 184
A. Induction of ISR 184
B. Signal Perception and Priming During the Development of ISR 185
VII. Techniques to Further Elucidate Long-Distance Signaling 186
VIII. Concluding Remarks 188
References 189
Chapter 5: Systemic Acquired Resistance 206
I. Introduction 207
A. Systemic Acquired Resistance 208
B. Other Forms of Induced Resistance 209
II. The Biological Spectrum of SAR 210
III. The Induction of SAR 210
A. Necrotizing Pathogens 210
B. The Hypersensitive Response 211
C. Is Pathogen-Induced Necrosis Needed for SAR Induction? 212
D. Pathogen-Produced Inducers of SAR 214
E. Chemical Induction of SAR 214
1. Salicylic acid 215
2. 2,6-Dichloroisonicotinic acid 215
3. Acibenzolar-S-methyl 216
4. Tiadinil 217
5. Other chemical inducers 217
IV. Systemic Biochemical Changes 218
A. Pathogenesis-Related Proteins 218
B. Other Proteins 219
C. SA Accumulation 220
V. How SAR Protects Plants Against Pathogens 221
A. Priming 221
B. Protection Against Fungi and Oomycetes 221
1. Cucurbits 221
2. Legumes 225
3. Solanaceous species 227
4. Arabidopsis 229
5. Japanese pear 230
6. Cereals 230
C. Protection Against Bacteria 231
1. Examples of induced resistance to bacterial pathogens 231
2. How SAR protects against bacterial pathogens 232
D. Protection Against Viruses 234
1. Decrease in lesion size and number 234
2. Inhibition of virus replication 235
3. Inhibition of cell-to-cell movement 235
4. Inhibition of systemic movement 235
5. Does SA induce a different form of resistance to viruses? 236
E. Mechanisms of Defense in Summary 237
1. Enhancing basal defense 237
B. What Don’t We Know? 240
VI. Concluding Comments 242
Acknowledgment 242
References 242
Chapter 6: Rhizobacteria-Induced Systemic Resistance 256
I. Introduction 257
A. PAMP- And Effector-Triggered Immunity 257
B. Systemic Acquired Resistance or Salicylic Acid-Induced Systemic Resistance 258
C. Rhizobacteria-Induced Systemic Resistance 259
D. Rhizobacteria Known to Trigger ISR 260
E. Scope of this Review 266
II. Recognition 266
A. Flagella 267
B. Lipopolysaccharides 273
C. Biosurfactants 276
D. N-acyl-L-homoserine lactone 278
E. N-alkylated benzylamine 279
F. Siderophores 279
1. Pseudobactins 280
2. SA and SA-containing siderophores 284
G. Antibiotics 286
1. 2,4-Diacetylphloroglucinol 286
2. Pyocyanin 287
H. Volatiles 288
I. Exopolysaccharides 290
J. Other Bacterial Determinants 291
III. Signalling in Rhizobacteria-Induced Systemic Resistance 291
A. The Arabidopsis–Pseudomonas fluorescens WCS417r System: A Paradigm for SA-Independent ISR Signalling 291
B. SA-Dependent ISR Signalling 296
C. SA-Dependent and SA-Independent Signalling 297
IV. Final Remarks 298
References 299
Chapter 7: Plant Growth-Promoting Actions of Rhizobacteria 316
I. Introduction 317
II. Modes of Action 318
A. Plant Growth-Promoting Substances 318
1. Auxins 319
2. Cytokinins 324
3. Gibberellins 325
4. Ethylene 326
5. Abscisic acid 328
B. Nitrogen Transformations 329
1. Biological nitrogen fixation 329
2. Nitrate uptake by roots as affected by bacteria 329
3. Denitrification 330
C. Phosphate and Micronutrient Availability 331
1. Phosphate 331
2. Vitamins 331
3. Iron and other microelements 331
D. Emerging Signals 332
1. Signals related to QS 332
2. Volatile compounds 333
3. Nitric oxide 333
E. Biocontrol in the Rhizosphere 334
1. Competition 334
2. Antibiosis 335
III. Agricultural Aspects and Relevance 337
A. PGPR and Endophytes—Role of Bacterial Numbers 337
B. PGPR and Other Symbiotic Systems such as Rhizobium-Legumes 338
C. Vegetative Growth and Grain Filling 339
D. Inoculant Technology 339
E. Probiotics in Agriculture 341
IV. Perspectives 341
Acknowledgments 342
References 343
Chapter 8: Interactions Between Nonpathogenic Fungi and Plants 354
I. Introduction 355
II. Interactions Between Plants and Endophytic Fungi 356
A. Plants and AM Fungi 356
1. Plant root colonization 357
2. Improvement of plant nutrition 357
3. Induction of plant resistance 359
B. Plants and Other Endophytic Fungi 362
1. Piriformospora indica 362
2. Binucleate Rhizoctonia 364
III. Interactions Between Plants and Free-Living Opportunistic Symbiotic Fungi 365
A. Plants and Trichoderma spp. BCAs 365
1. Plant root colonization 366
2. Improvement of plant nutrition 368
3. Induction of plant resistance 369
B. Plants and Nonpathogenic F. oxysporum 375
C. Plants and Nonpathogenic Penicillium spp., Phoma spp., and Pythium oligandrum 377
IV. Overview of Plant Defense Mechanisms Induced by Nonpathogenic Fungi 380
References 383
Chapter 9: Priming of Induced Plant Defense Responses 394
I. Introduction 395
II. Types of IR 395
A. Systemic Acquired Resistance (SAR) 395
B. Resistance Induced by Beneficial Microorganisms 396
1. Induced systemic resistance (ISR) 396
2. Resistance induced by symbiotic fungi 397
C. Resistance Induced by Chemicals 397
1. Synthetic SA analogs 397
2. beta-Aminobutyric acid 398
D. Resistance Induced by Wounding 398
E. Resistance Induced by Modifications of Primary Metabolism 399
III. Priming is a Mechanism of IR 400
A. History 400
B. Elucidation of Priming in Parsley Cell Cultures 400
C. Priming in SAR 402
1. Tobacco 402
2. Arabidopsis 402
3. Other species 404
D. Priming Induced by Beneficial Microorganisms 405
1. Priming in ISR 405
2. Priming in beneficial interactions other than ISR 406
3. Priming by bacterial lipopolysaccharides 407
E. Priming in BABA-IR 407
1. Biotic stress 407
2. Abiotic stress 409
F. Priming in Wound-Induced Resistance 409
1. Priming in IR to herbivores 409
2. Priming between plant species 411
G. Priming by Modifications in Primary Metabolism 411
IV. Relevance of Priming in Plant Production 412
A. Costs and Benefits of Priming 412
B. Exploiting Priming in Greenhouse and Field 413
V. Conclusions 417
Acknowledgments 417
References 417
Chapter 10: Transcriptional Regulation of Plant Defense Responses 430
I. Plant Immune Signaling Pathways 431
II. Defense Signaling Regulatory Compounds 433
A. Jasmonate Signal Transduction 433
B. Ethylene Signal Transduction 435
C. SA Signal Transduction 437
III. Transcription Factors Regulating Plant Defense Gene Expression 440
A. AP2/ERF Transcription Factors 441
B. MYB Transcription Factors 443
C. MYC Transcription Factors 445
D. bZIP Transcription Factors 446
E. WRKY Transcription Factors 448
IV. Regulation of Plant Defenses at the Chromosomal Level 453
A. Chromatin Modifications and Gene Expression 453
B. Chromatin Modifications in Plants 454
C. Chromatin Modifications at Promoters Involved in Innate Immunity 455
1. The SA pathway 455
2. The JA pathway 457
Acknowledgment 459
References 459
Chapter 11: Unexpected Turns and Twists in Structure/Function of PR-Proteins that Connect Energy Metabolism and Immunity 472
I. Historical Perspective Leading to the Recognition of Innate Immunity in Plants 473
A. Plant Immunity Involves Pathogenesis-Related (PR) Proteins 474
B. Definition and Classification of PR-proteins 475
II. Roles of PR-proteins Revealed by Studies of PR gene Expression 477
A. Cross-talk Between Overlapping Biotic and Abiotic Stress Response Pathways and Hormone Signaling Precludes Identification of Clear Roles for PR-proteins 477
B. Nutrient Acquisition Strategies of Pathogens Are Associated with Distinct PR gene Sets 479
C. The Connection Between Energy Balance and Immunity 482
III. PR-5 Protein Structure Reveals the Primitive Relationship Between Pathogen Defense and Energy Balance 483
A. Structural Features of PR-5 Proteins 483
B. Function of PR-5 Proteins in Plants 483
C. Information on Plant PR-5 Proteins in Genomic Databases 487
D. Comparison of THN Domain with C1q-TNF Domains 496
E. THN Domain Proteins and C1q-TNF Domains Across Phyla 502
IV. Directions in Which Current Classification or Definition of PR-proteins May Change in the Coming Years as Advanced Functional Studies Progress 505
References 507
Chapter 12: Role of Iron in Plant-Microbe Interactions 524
I. Introduction 525
II. Strategies of Iron Acquisition and Homeostasis by Plants and Microorganisms 527
A. Plants 527
1. Iron uptake by plant roots 527
a. Iron uptake in grasses (Strategy II 527
b. Iron uptake in the non?grass model plant 529
2. Organic compound exudates from roots and iron uptake 530
3. Regulation of high-affinity iron-transport systems 530
a. Transcriptional and translational regulation 530
b. Hormonal regulation 532
B. Microorganisms 532
1. Siderophore-mediated iron uptake 532
a. Iron uptake by fluorescent pseudomonads 533
b. Iron uptake in Erwinia 535
2. Regulation of the high-affinity iron-transport systems 536
III. Reciprocal Interactions Between Plants and Microorganisms During Their Saprophytic Life 538
A. Impact of Plant Iron Acquisition on Associated Microbes 538
1. Diversity 538
2. Activity 542
B. Impact of Microbial Iron Acquisition on the Host Plant 543
1. Plant health 543
a. Microbial antagonism 544
b. Induced systemic resistance 547
2. Plant growth and nutrition 549
IV. Reciprocal Interactions Between Plants and Microorganisms During Pathogenesis 551
A. Iron And Microbial Virulence: Role of High-Affinity Iron Assimilation Systems 552
1. Siderophore-controlled iron acquisition and Er. chrysanthemi pathogenicity 554
2. Siderophore-controlled iron acquisition and Er. amylovora pathogenicity 556
3. Siderophore-mediated iron acquisition and pathogenicity of ascomycete fungi 558
4. High-affinity iron acquisition and Ustilago maydis pathogenicity 559
B. Iron and Plant Defense 560
1. Iron homeostasis in wheat upon infection by Blumeria graminis 560
2. Involvement of ferritin in the response of potato to Phytophthora infestans 561
3. Iron homeostasis and resistance of Arabidopsis to Er. chrysanthemi 562
V. Conclusions 563
References 565
Chapter 13: Adaptive Defense Responses to Pathogens and Insects 584
I. Introduction 585
II. Co& hyphen
III. Portals of Entry and Activation of Defenses 589
A. Microbial Invasion Strategies: From Accessing the Apoplast to Haustoria Formation 590
B. Defense Pathway Activation by Microbes 591
C. Herbivore-Feeding Guilds: Mechanisms to Violate the Integrity of Plant Cells 592
1. Tissue-damaging herbivores: Modes of feeding 593
2. Tissue-damaging herbivores: Defense signaling and discerning the role of injury 594
3. Phloem-feeding hemipterans 596
IV. Perceiving Pathogen and Pest Visitations: The Role of Microbial and Herbivore Elicitors and Molecular Patterns 597
A. PAMPs, Pattern-Recognition Receptors, and BAK1 597
B. Elicitors of Plant Origin 598
C. Herbivore Elicitors 600
1. Lipid signals without receptors: Volicitin and caeliferin 601
2. Peptide elicitors of volatile emissions: Inceptin and beta-glucosidase 604
3. Oviduct secretions: Elicitors of defense gene expression and volatile emissions 605
4. Chitin 607
5. Salivary proteins as elicitors 607
a. Lysozyme 607
b. Hemipteran saliva 608
V. Integrating Signals and Activating Defenses 609
A. Mitogen-Activated Protein Kinase Signaling Cascades 610
B. Linking PAMPs to SA-, JA-, and ET-Regulated Defense Responses 613
VI. Adaptations to Unfriendly Hosts: Effectors and Evasion Tactics 614
A. Microbial Effectors 614
B. Herbivore Effectors 615
1. Effectors in regurgitant 615
2. Effectors in saliva 616
a. Glucose oxidase: A salivary effector that suppresses wound signaling 616
b. Decoy defenses: Suppressing effective defenses using SA–JA cross-talk 617
c. Antagonizing wound healing with calcium-binding proteins 619
d. Salivary oxidases and the Redox Hypothesis 620
e. Specialist insects: Tolerating toxic phytochemicals 621
VII. Effector-Triggered Immunity: Resistance to Pathogens and Pests 622
A. The Guard and Decoy Models 622
B. Plant–Herbivore Gene-for-Gene Interactions 623
1. Resistance genes 623
2. Mi1.2: One gene—many herbivores 624
3. Medicago resistance to aphids: A JA-dependent event 625
VIII. Summary and Future Prospects 626
Acknowledgments 628
References 628
Chapter 14: Plant Volatiles in Defence 646
I. Introduction to Volatile Organic Compounds (VOCs) From Plants 647
II. Herbivore-Produced Elicitors and Suppressors of Plant VOC Emission 649
III. Biosynthesis of Plant VOCs 652
A. Linoleic Acid/Octadecanoid Pathway-Related Compounds 652
B. Phenylalanine-Derived Volatiles 654
C. Terpenoids 655
D. Methanol 656
E. Ethylene 657
IV. Volatile Metabolism in Plant Trichomes 657
A. Trichome Function and Occurrence 657
B. Trichome Metabolomics and Transcriptomics 658
V. Volatile Defence Hormones MeJA, MeSA and Ethylene 660
VI. VOC Signals Are Influenced by Abiotic Factors and Plant Developmental Stage 665
VII. Natural Variation in VOC Production 668
VIII. VOC-Mediated Specificity of Indirect Defences 672
IX. VOCs as Alarm Signals for Neighbouring Plants 676
A. Transcriptional Responses to VOC Exposure 676
B. Priming of Plant Defences by Volatiles 679
References 684
Chapter 15: Ecological Consequences of Plant Defence Signalling 700
I. Introduction 701
II. Signalling at Three Different Levels 702
A. Local Signalling 702
1. Pathogen recognition 702
2. Resistance hormones 703
3. Further plant hormones 704
4. Cross-talk between growth and defence 706
B. Systemic Within-Plant Signalling 706
1. Systemic signals triggering herbivore resistance 707
2. Systemic signals triggering pathogen resistance 708
3. Small RNA signalling 709
4. Airborne systemic signals 709
C. Airborne Plant–Plant Communication 710
1. Does ‘plant–plant communication’ exist? 710
2. Airborne resistance induction to herbivores and pathogens 710
3. Mechanisms of airborne plant–plant communication 712
4. Priming by VOCs 713
III. Costs of Induced Resistance 713
A. Allocation Costs 714
B. Ecological Costs 716
1. Trade-offs with resistance to insects 716
2. Trade-offs with mutualistic symbioses 718
3. Does induced resistance alter phytobacterial communities? 719
4. Ecological costs of resistance to biotrophic versus necrotrophic pathogens 719
IV. Resistance Induced by Mutualistic Micro-organisms 720
A. Resistance Mediated by Plant Growth-Promoting Rhizobacteria (PGPR) 720
B. Resistance Induction by Mycorrhiza 722
V. Defence Signalling at the Level of Plant Individual, Community and Evolution 723
A. Variable Resistance at the Genetic Level 723
B. Variable Resistance at the Phenotypic Level 724
C. Plant–Plant Communication at the Community Level? 724
D. Evolutionary Considerations 726
E. Predicting Patterns of Induced Resistance Responses 726
1. Growth-differentiation balance hypothesis (GDBH) and optimal defencehypothesis (ODH) 727
2. Carbon/nutrient balance hypothesis (CNBH) and resource availabilityhypothesis (RAH) 728
VI. Conclusions and Outlook 731
Acknowledgments 732
References 732
Author Index 750
Subject Index 772
Color Plates 788