Phytohormones : a window to metabolism, signaling and biotechnological applications

Abiotic and biotic stresses adversely affect plant growth and productivity. The phytohormones regulate key physiological events under normal and stressful conditions for plant development. Accumulative research efforts have discovered important roles of phytohormones and their interactions in regulation of plant adaptation to numerous stressors. Intensive molecular studies have elucidated various plant hormonal pathways; each of which consist of many signaling components that link a specific hormone perception to the regulation of downstream genes. Signal transduction pathways of auxin, abscisic acid, cytokinins, gibberellins and ethylene have been thoroughly investigated. More recently, emerging signaling pathways of brassinosteroids, jasmonates, salicylic acid and strigolactones offer an exciting gateway for understanding their multiple roles in plant physiological processes. {OCLCbr#A0}At the molecular level, phytohormonal crosstalks can be antagonistic or synergistic or additive in actions. Additionally, the signal transduction component(s) of one hormonal pathway may interplay with the signaling component(s) of other hormonal pathway(s). Together these and other research findings have revolutionized the concept of phytohormonal studies in plants. Importantly, genetic engineering now enables plant biologists to manipulate the signaling pathways of plant hormones for development of crop varieties with improved yield and stress tolerance. {OCLCbr#A0}This book, written by internationally recognized scholars from various countries, represents the state-of-the-art understanding of plant hormones' biology, signal transduction and implications. Aimed at a wide range of readers, including researchers, students, teachers and many others who have interests in this flourishing research field, every section is concluded with biotechnological strategies to modulate hormone contents or signal transduction pathways and crosstalk that enable us to develop crops in a sustainable manner. Given the important physiological implications of plant hormones in stressful environments, our book is finalized with chapters on phytohormonal crosstalks under abiotic and biotic stresses.{OCLCbr#A0}{OCLCbr#A0}{OCLCbr#A0}{OCLCbr#A0}{OCLCbr#A0}{OCLCbr#A0} Preface 6 Contents 8 Contributors 10 Auxin in Plant Growth and Stress Responses 13 Introduction 14 Auxin Biosynthesis and Metabolism 15 Auxin Biosynthesis 15 A Simple Two-Step Biosynthesis Pathway for Auxin 16 Conversion of Trp to IPA by TAA1 16 The Rate-Limiting Step Catalyzed by YUC in Auxin Biosynthesis Pathway 17 A Second Pathway Converting Trp to IAA by Cytochrome P450s (IAOx Pathway) 19 Auxin Conjugation and Degradation 20 IAA Conjugation 20 IAA Degradation 21 Auxin Homeostasis Control in Response to Environmental Stresses 21 Auxin and Plant Response to Salt Stress 22 Auxin and Plant Response to Drought Stress 23 Auxin Perception, Transduction, and Attenuation 25 Auxin Perception and Signaling Transduction 25 ABP1-Mediated Auxin Perception and Signaling Transduction 26 TIR1-Mediated Auxin Perception and Signaling 28 SKP2A-Mediated Auxin Perception and Signaling 29 Auxin Signaling Attenuation 30 Auxin Signaling Pathway Mediates Plant Responses to Abiotic Stresses 31 Biotechnological Manipulation of Auxin Biosynthesis and Signaling in Agriculture 33 Conclusions and Future Perspectives 37 References 38 Abscisic Acid Implication in Plant Growth and Stress Responses 48 ABA Metabolism and Transportation 49 Signal Perception and Execution of ABA-Induced Responses 51 Receptor and Signal Transduction: PYR/PYL-PP2C-SnRK2 51 SnRK2 Substrates 53 Components Other than the SnRK2 Pathway 55 Biotechnological Manipulation of ABA Homeostasis and Signalling in Agriculture 57 References 59 Cytokinin Regulation of Plant Growth and Stress Responses 66 Biosynthesis and Metabolism of CKs 67 Signal Perception and Execution of CK-Induced Responses 69 Cytokinin Receptors 70 Cytokinin Phosphotransfer Proteins 73 Cytokinin Response Regulators 74 Improvement of Plant Productivity with Biotechnological Manipulation of Cytokinin Biosynthesis and Signaling 77 References 81 Roles of Ethylene in Plant Growth and Responses to Stresses 91 Ethylene Biosynthesis 92 Ethylene Biosynthetic Pathway 92 Ethylene Biosynthetic Genes 93 Regulation of Ethylene Biosynthesis 94 Transcriptional Regulation 94 Posttranslational Regulation 95 Signal Perception and Execution of Ethylene-Induced Responses 96 Ethylene Signal Transduction Pathway 96 Ethylene Receptor 97 CTR1 99 EIN2 100 EIN3/EILs and ERFs 101 Regulation of Plant Growth and Development by Ethylene 102 Seed Germination 102 Vegetative Growth 102 Flower Development 103 Fruit Ripening 104 Leaf Senescence 105 Regulatory Roles of Ethylene in Stress Responses 106 Ethylene Cross Talk with Other Hormones 109 Ethylene–Auxin 109 Ethylene–ABA 111 Biotechnological Manipulation of Ethylene Biosynthesis and Signaling in Agriculture 112 Fruit and Flower Plants 112 Major Crops 113 Rice 113 Wheat 115 Maize 115 Legume 116 Perspectives 117 References 118 Gibberellin Implication in Plant Growth and Stress Responses 129 Brief History of Gibberellin Research 130 Gibberellin Metabolism 130 Biosynthesis and Catabolism 130 Regulation of Gibberellin Metabolism 135 The Gibberellin Signaling Pathway 138 DELLA Proteins: The Transcriptional Regulators That Repress GA Signaling 138 The DELLA Gene Family 138 Sequence Features of DELLA Proteins 140 GA Regulation of DELLA Proteins and the Role of Their Conserved Domains 141 The F-Box Proteins GID2/SLY1 Mediate the GA-Induced Degradation of DELLAs 142 GID2/SLY1 Encodes F-Box Proteins That Interact with DELLAs in Response to GAs 142 Phosphorylation of DELLAs and Their GA-Induced Degradation 144 GID1 Is a GA Receptor That Promotes GA-Dependent Interaction of DELLA with GID2/SLY1 145 Identification of a GA Receptor 145 GID1 Interacts with DELLAs in a GA-Dependent Manner and Promotes Their Degradation 147 Structure of the GID1 Receptor 148 DELLAs Are Inactivated by the GID1-GA Complex Previous to Their Degradation 149 Evolution of the GA-GID1-DELLA Regulatory Mechanism 150 Regulation of Downstream Processes by DELLA Proteins 151 DELLA Proteins Provoke Changes in the Transcriptome 151 DELLA Proteins Have Transcriptional Activation Activity 152 “Sociology” of DELLA Proteins: Preferred Interaction with Transcription Factors 152 Non-genomic Responses Regulated by DELLA Proteins 155 SPINDLY: The Black Sheep in GA Signaling? 155 Gibberellins as Targets for Biotechnological Applications 157 References 160 Brassinosteroids Implicated in Growth and Stress Responses 172 Introduction 173 Brassinosteroid Biosynthesis 175 Brassinosteroids and Abiotic Stress 180 Signal Transduction of Brassinosteroids 185 Brassinosteroid Receptor 185 Substrates of BRI1 Kinase 187 Downstream Events of Brassinosteroid Signalling 189 A Class of Brassinosteroid-Activated Transcription Factors and Their Regulation 189 Brassinosteroid Signalling and Stress Tolerance 192 Conclusion Remarks 193 References 193 Salicylic Acid and Defense Responses in Plants 200 Introduction 201 Salicylic Acid Biosynthesis 202 The PAL Pathway 203 The ICS Pathway 205 Signal Perception and Execution of Salicylic Acid-Induced Responses 208 SA Receptors 208 NPR1-Dependent SA Signaling 210 NPR1-Independent SA Signaling 212 Biotechnological Manipulation of Salicylic Acid Signaling and Biosynthesis in Agriculture 214 References 218 Jasmonates in Plant Growth and Stress Responses 229 Introduction 230 JA Biosynthesis 232 JA Metabolism 236 Perception of JA–Ile and Cross-Talk to Other Hormones 238 JA/JA–Ile-Regulated Metabolism of Secondary Compounds 244 JA/JA–Ile in Biotic Interactions of Plants 245 JA/JA–Ile in Abiotic Stress Response of Plants 249 JA/JA–Ile in Plant Growth and Development 250 Applied Aspects on Jasmonates 254 Conclusions 257 References 257 Strigolactones: Biosynthesis, Synthesis and Functions in Plant Growth and Stress Responses 272 Introduction 272 Strigolactone Biosynthesis 273 Strigolactone Function in Plant Growth 276 Role of Strigolactones in Shoot Development 276 Role of Strigolactones in Shoot Secondary Growth 277 Role of Strigolactones in Root Development 277 Role of Strigolactones in Adventitious Root Formation 278 Strigolactone Signalling and Transport 279 Strigolactone Function in Stress Responses 282 Nutrient 282 Light 284 Strigolactone Chemistry 284 Natural SLs 284 Stereochemistry 285 Analogues 286 Mimics 286 Mode of Action Mechanism 287 Concluding Remarks 289 References 289 Phytohormonal Crosstalk Under Abiotic Stress 296 Introduction 297 Abscisic Acid Crosstalk Under Abiotic Stress Conditions 298 Jasmonates Crosstalk Under Abiotic Stress Conditions 301 Salicylic Crosstalk Under Abiotic Stress Conditions 303 Ethylene Crosstalk Under Abiotic Stress Conditions 304 Auxin Crosstalk Under Abiotic Stress Conditions 307 Gibberellin Crosstalk Under Abiotic Stress Conditions 311 Cytokinin Crosstalk Under Abiotic Stress 313 Brassinosteroid Crosstalk Under Abiotic Stress 314 Strigolactone Crosstalk Under Abiotic Stress 316 Conclusions and Prospects 317 References 318 Plant Hormone Crosstalks Under Biotic Stresses 329 Introduction 330 Salicylic Acid Signaling Pathway 330 Other Plant Hormones and Their Interactions with SA 333 Jasmonic Acids 333 Ethylene 336 Abscisic Acid 337 Cytokinins 340 Gibberellic Acids 342 Auxin 343 Brassinosteroids 344 Concluding Remarks and Future Perspectives 345 References 347 About the Editors 357 Index 359 Abiotic and biotic stresses adversely affect plant growth and productivity. The phytohormones regulate key physiological events under normal and stressful conditions for plant development. Accumulative research efforts have discovered important roles of phytohormones and their interactions in regulation of plant adaptation to numerous stressors. Intensive molecular studies have elucidated various plant hormonal pathways; each of which consist of many signaling components that link a specific hormone perception to the regulation of downstream genes. Signal transduction pathways of auxin, abscisic acid, cytokinins, gibberellins and ethylene have been thoroughly investigated. More recently, emerging signaling pathways of brassinosteroids, jasmonates, salicylic acid and strigolactones offer an exciting gateway for understanding their multiple roles in plant physiological processes. ℗ At the molecular level, phytohormonal crosstalks can be antagonistic or synergistic or additive in actions. Additionally, the signal transduction component(s) of one hormonal pathway may interplay with the signaling component(s) of other hormonal pathway(s). Together these and other research findings have revolutionized the concept of phytohormonal studies in plants. Importantly, genetic engineering now enables plant biologists to manipulate the signaling pathways of plant hormones for development of crop varieties with improved yield and stress tolerance. ℗ This book, written by internationally recognized scholars from various countries, represents the state-of-the-art understanding of plant hormones ́ biology, signal transduction and implications. Aimed at a wide range of readers, including researchers, students, teachers and many others who have interests in this flourishing research field, every section is concluded with biotechnological strategies to modulate hormone contents or signal transduction pathways and crosstalk that enable us to develop crops in a sustainable manner. Given the important physiological implications of plant hormones in stressful environments, our book is finalized with chapters on phytohormonal crosstalks under abiotic and biotic stresses.℗ ℗ ℗ ℗ ℗ ℗ Front Matter....Pages i-xi Auxin in Plant Growth and Stress Responses....Pages 1-35 Abscisic Acid Implication in Plant Growth and Stress Responses....Pages 37-54 Cytokinin Regulation of Plant Growth and Stress Responses....Pages 55-79 Roles of Ethylene in Plant Growth and Responses to Stresses....Pages 81-118 Gibberellin Implication in Plant Growth and Stress Responses....Pages 119-161 Brassinosteroids Implicated in Growth and Stress Responses....Pages 163-190 Salicylic Acid and Defense Responses in Plants....Pages 191-219 Jasmonates in Plant Growth and Stress Responses....Pages 221-263 Strigolactones: Biosynthesis, Synthesis and Functions in Plant Growth and Stress Responses....Pages 265-288 Phytohormonal Crosstalk Under Abiotic Stress....Pages 289-321 Plant Hormone Crosstalks Under Biotic Stresses....Pages 323-350 Back Matter....Pages 351-361