Secondary Metabolites and Volatiles of PGPRs in Plant-Growth Promotion

This contributed volume explores how plant growth-promoting rhizobacterias (PGPR) provide a wide range of benefits to the plant. Further, it discusses the key roles PGPR play in nutrient acquisition and assimilation, improved soil texture, secreting, and modulating extracellular molecules. The book outlines how plant secondary metabolites are natural sources of biologically active compounds used in a wide range of applications, and surveys the significant role of volatile organic compounds (VOCs) in plant communication by mediating above- and below-ground interactions between plants and the surrounding organisms. This volume compiles research from leading scientists from across the globe, linking the translation of basic knowledge to innovative applied research. The book focuses on the following three categories: 1) understanding the secondary metabolites produced by PGPR, the signaling mechanisms and how they affect plant growth, 2) the plausible role ofvolatile organic compounds produced by PGPR, their role and the signaling mechanism for plant growth promotion, and 3) Applications of VOCs and secondary metabolites of PGPR for seed germination, plant growth promotion; stress tolerance and in-plant health and immunity. About the Book Contents About the Editors Chapter 1: Plant Growth-Promoting Rhizobacteria (PGPR): An Overview 1 Introduction 2 Mechanisms of Plant Growth Promotion 2.1 Production of Phytohormone 2.1.1 Indole-3-Acetic Acid (IAA) 2.1.2 Gibberellic Acid (GA3) 2.2 Nitrogen Fixation 2.3 Phosphate Solubilization 2.4 Zinc and Iron Solubilization 2.5 Potash Solubilization 3 Antimicrobial Properties Against Phytopathogens 3.1 Biocontrol Mechanisms 3.1.1 Siderophore Production 3.1.2 Cyanide Production 3.1.3 Antibiotic Production and Antifungal Activity 4 Conclusion References Chapter 2: Metabolomics as a Tool to Study Volatile Organic Compounds Produced by Plant Growth-Promoting Rhizobacteria 1 Overview of the Study of the Plant Growth-Promoting Rhizobacteria (PGPR) Volatile Compounds 2 Volatile Compound Screening in the Metabolomic Analysis 3 Bioinformatics Tools for the Interpretation of Metabolomics Data 3.1 Data Processing 3.2 Chemometrics: Statistical Validation 3.3 Software: Identify a Metabolite and Metabolic Pathway 4 Application of the Metabolomic Analysis for the Elucidation of Volatiles Produced by Plant Growth-Promoting Rhizobacteria (PGPR) 5 Challenges for the Metabolomic Analysis of Rhizobacteria Volatiles 6 Final Considerations References Chapter 3: The Role of PGPR-Secondary Metabolites on Plant Photosynthesis 1 Introduction 2 The Effect of PGPR on the Net CO2 Photosynthetic Rate 3 The Effect of PGPR on the Photosystem II (PSII) Efficiency 4 PGPR and Their Role on the Chlorophylls a and b 5 PGPR and Plant Transpiration Rate 6 PGPR and Their Effect on Stomatal Conductance 7 Conclusion References Chapter 4: Effect of Volatile Organic Compounds (VOCs) and Secondary Metabolites Produced by Plant Growth-Promoting Rhizobacteria (PGPR) on Seed Quality 1 Introduction 1.1 Brief Overview of the Rhizobacteria-Plant Association and Its Benefit 2 Effects of PGPR on Physiological and Health Seed Quality 3 Effect of PGPR in Biopriming Seed Quality 4 Conclusion and Future Perspective References Chapter 5: The Role of PGPR-Polar Metabolites, Metal-Chelator Compounds and Antibiotics on Plant Growth 1 Introduction 2 Polar Metabolites 2.1 Organic Acids 3 Siderophore 4 Antibiotics 5 Amino Acids 6 Sugars 7 Future Perspectives References Chapter 6: Inhibition of Bacterial and Fungal Phytopathogens Through Volatile Organic Compounds Produced by Pseudomonas sp. 1 Introduction 2 Microorganisms Emitting Volatile Organic Compounds 2.1 Production of VOCs by Consortium of Different Microbes 3 Bacterial Volatiles: Tool to Biocontrol of Phytopathogens 4 Pseudomonas Volatilome 4.1 Role of Pseudomonas Volatilome in Biocontrol of Phytopathogens 4.2 Role of Secondary Metabolites Produced by Pseudomonas spp. in Plant Disease Control 4.3 Antibiotics Produced by Pseudomonas spp. 5 Conclusion References Chapter 7: How Phytohormones Synthesized by PGPR Affect Plant Growth? 1 Introduction 2 Indole-3-Acetic Acid (IAA) 3 Gibberellic Acid (Gibberellin) 4 Cytokinin 5 Ethylene 6 Abscisic Acid 7 Concluding Remarks References Chapter 8: The Role of PGPR Secondary Metabolites in Alleviating Allelopathic Effects (Biotic Stress) and Induced Tolerance in Plants 1 Introduction 2 Concepts About Plant Growth-Promoting Rhizobacteria (PGPR) 2.1 PGPR and Production of Secondary Metabolites 2.2 How PGPR Induce Tolerance in Plants Under Environmental Stress 3 Allelopathic Compounds Produced by Plants 3.1 Cover Plants with Allelopathic Potential 3.2 Effects of Cultivation Systems and Plant Phenological Stages on Secondary Metabolite Production 4 Final Considerations References Chapter 9: Role of Actinomycetes in Mitigating the Impact of Climate Change: Mechanisms of Action and Perspectives 1 Introduction 2 Plant Growth-Promoting Bacteria and Induced Systemic Resistance 3 Actinomycetes as Mitigators of Climate Change 3.1 Drought Stress 3.2 Salinity Stress 3.3 Alkalinity Stress 3.4 Temperature Changes 4 Conclusions and Future Perspectives References Chapter 10: Metabolites of Bacillus spp. to Control Fungal Phytopathogens 1 Introduction 2 Phytomicrobiome: The Beneficial Interaction 3 Fungal Phytopathogens 4 Biocontrol of Fungal Phytopathogens 4.1 Role of Bacillus spp. in Fungal Disease Control 5 Secondary Metabolites from Bacillus spp. Involved in the Biocontrol of Fungal Pathogens 5.1 Hydrogen Cyanide (HCN) 5.2 Siderophore Production 6 Antibiotics Produced by PGPR 6.1 Antibiotics Produced by Bacillus spp. 7 Role of Bacillus Volatilome to Control Phytopathogens 8 Conclusion References Chapter 11: Antifungal Antibiotics Biosynthesized by Major PGPR 1 Introduction 2 Inorganic Agrochemicals 3 Biocontrol Approach 4 Microbial Volatile Compound (mVOC) Antagonism of Phytopathogens 4.1 mVOC Antagonism of Fungi 4.2 mVOC Antagonism of Bacteria 4.3 mVOC Antagonism of Oomycetes 4.4 mVOC Antagonism of Virus 5 Structural Differences of mVOC That Influence Their Inhibitory Function 6 Mechanisms of Volatile Microbial Compounds Against Plant Pathogens 7 Intrinsic Antibiotic Resistance 8 PGPR as Biocontrol Agents Induce Induced Systemic Resistance (ISR) and Systemic Acquired Resistance (SAR) 9 Major Antifungal Antibiotics of PGPR 9.1 Antifungal Antagonist Antibiotics Against Plant Pathogens 10 Regulation of Antibiotic Synthesis 10.1 GacS/GacA System 10.2 N-acyl Homoserine Lactone (NHL) and Sigma Factors in Antibiotic Biosynthesis 10.2.1 Quorum Sensing 10.3 Virulent Factor Regulation 10.4 Type VI Secretion Systems (T6SS) 10.5 Type III Secretion Systems (T3SS) 10.6 Outer Membrane Protein F Gene (OprF) 10.7 The Ecological Role of PGPR Antifungal Antibiotics 11 Role of PGPR Antifungal Antibiotics in ISR 11.1 Ribosomal Peptides (rps) 11.2 Nonribosomal Peptides (nrps) 11.3 Bacteriocins 11.4 AMP Enzymes 11.5 Polykedties (pks) 11.6 Lipopeptides (Thiotemplate NRPS) 11.7 Siderophores (Thiotemplate NRPS) 11.8 Non-thiotemplate NRPS 12 Volatile Compounds 12.1 Volatile Inorganic Compounds 12.2 Nonvolatile Microbial Compounds 12.3 Alcohols 13 Conclusion 14 Future Perspective References Chapter 12: Extreme Environments as Potential Sources for PGPR 1 Introduction 2 What Is an Extreme Environment? 3 Microbial Diversity in Extreme Environments 4 Relevant Applications of Extremophiles 5 Approaches of Extremophile Use in Plant Growth Promotion 5.1 Biotopes and Ecological Niches of Isolation 5.2 Plant-Associated Extremophiles 5.3 By-Products of Extremophiles 6 Key Features of Plant Growth-Promoting Extremophiles 6.1 Abiotic Stress Tolerance 6.1.1 Drought Stress 6.1.2 Salinity Stress 6.1.3 Cold Stress 6.1.4 Acid/Alkaline Stress 6.2 Soil Fertility and Bioremediation 6.3 Biocontrol 7 Challenges and Perspectives of PGP Extremophile Use in Agriculture 8 Conclusion References Chapter 13: Commercial and Technological Aspects of Bacillus spp. PGPR 1 Introduction 2 Application of Bacillus in Agriculture 3 Commercialization of Bacillus 4 Technological Aspects 5 Conclusion and Future Prospects References Chapter 14: Siderophores and Their Applications in Sustainable Management of Plant Diseases 1 Introduction 2 Characteristic Features of Siderophores 3 Classification of Siderophores Based on Chemical Structure 3.1 Types of Siderophore 4 Siderophore Classification Based on Their Source 4.1 Fungal Siderophores 4.2 Bacterial Siderophores 4.3 Cyanobacterial Siderophores 4.4 Actinomycete Siderophores 4.5 Mammalian Siderophores 4.6 Phytosiderophores/Plant Siderophores 4.7 Characteristic Features of Phytosiderophores 5 Biosynthesis of Siderophores 6 Applications of Siderophores 6.1 Plant Growth Promotion 6.2 Biocontrol Agent/Suppress the Plant Diseases 7 Conclusion References Chapter 15: Hydrolytic Enzyme Producing Plant Growth-Promoting Rhizobacteria (PGPR) in Plant Growth Promotion and Biocontrol 1 Introduction 2 Plant Growth-Promoting Rhizobacteria (PGPR) 3 Hydrolytic Enzymes 3.1 Role of Hydrolytic Enzyme 3.2 Mechanism of Hydrolytic Enzymes Against Phytopathogens 3.3 Types of Hydrolytic Enzymes 4 Importance of Rhizospheric Microbial Enzymes 5 Conclusion References Chapter 16: Fungal Hydrolytic Enzymes Produced by Plant Growth-Promoting Rhizobacteria (PGPR) 1 Introduction 2 PGPR Secretions 2.1 Hydrolytic Enzymes 2.2 Antibiotics 2.3 Siderophores 3 PGPR-Mediated Biocontrol 3.1 The PGPR Released Hydrolytic Enzymes 3.1.1 The Fungal Cell Wall: Weaker Link Chitinase Glucanase Protease Cellulase 4 Mycoparasitism in Antifungal Response 5 Induced Systemic Resistance (ISR) in Combating Fungi 6 Conclusions and Future Prospects References Chapter 17: Selection of Carbon Sources by Rhizobacteria – A Muster of Signalling Factors Governing Carbon Catabolite Repression 1 Introduction 2 Transport of Carbon Sources 2.1 Carbohydrate Transport 2.2 Dicarboxylate Transport 3 Carbon Catabolite Repression (CCR) 3.1 CCR Signalling in Escherichia coli 3.2 CCR Signalling in Bacillus subtilis 3.3 CCR Signalling in Pseudomonads 3.4 CCR Signalling in Rhizobia 3.5 CCR Signalling in Different Bacteria Dictating Carbohydrate Preference 4 Conclusion References Chapter 18: Plant Growth-Promoting and Biocontrol Metabolites Produced by Endophytic Pseudomonas fluorescence 1 Introduction 2 Plant Growth-Promoting Rhizobacteria (PGPR) 3 Concept of Endophytes 4 Biodiversity of Endophytes 4.1 Pseudomonas fluorescens 4.1.1 Occurrence of Pseudomonas fluorescence 4.2 Plant Growth Promoting and Biocontrol Substances Produced by Pseudomonas fluorescens 4.2.1 Indole-3-Acetic Acid (IAA) Production 4.2.2 Siderophore Production 4.2.3 Phosphate Solubilization 4.2.4 ACC-deaminase Activity of Pseudomonas fluorescens 4.3 Aggressive Root Colonization References Index