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Professor Peter Hedden graduated with BSc (1969) and PhD (1973) degrees in chemistry from the University of Bristol. After post-doctoral positions at the University of Göttingen, Germany, with Jan Graebe and at UCLA, USA, with Bernard Phinney, he joined East Malling Research Station, in Kent, United Kingdom in 1981. He moved to Long Ashton Research Station (LARS), Bristol, UK, in 1984 and then to Rothamsted Research after the closure of LARS in 2003. His main research interest throughout his career has been the biosynthesis of the gibberellin plant hormones, working initially on delineating the biosynthetic pathways, then on the isolation and characterization of the biosynthetic enzymes and latterly on their regulation by developmental and environmental factors. Current research includes exploiting the gibberellin biosynthesis and signal transduction pathways for the introduction of desirable traits into crop species.

Dr Steve Thomas graduated BSc from the University of Southampton in 1991. He gained a PhD in biochemistry at Bristol University in 1996. In the same year he started postdoctoral work at Long Ashton Research Station where he spent four years investigating the regulation of gibberellin biosynthesis and inactivation in sugar beet and Arabidopsis. He then spent three and a half years in Tai-ping Sun’s Laboratory at Duke University dissecting the signalling pathways controlling gibberellin-mediated degradation of DELLA proteins in Arabidopsis. In 2004, he returned to the UK to work with Dr Andy Phillips and Prof. Peter Hedden in the Hormone Signalling Group at Rothamsted Research as a Senior Scientist. He is currently a member of the 20:20 Wheat® Institute Strategic Programme at Rothamsted Research, with his research  focused on improving grain yields in wheat by manipulating plant hormone signalling.

List of Contributors xv

Preface xvii

1 Signal Achievements in Gibberellin Research: The Second Half-Century 1
Valerie M. Sponsel

1.1 Introduction 1

1.2 Gibberellin biosynthesis 6

1.3 Gibberellin signalling 17

1.4 Physiological responses to gibberellins 25

References 29

2 Gibberellin Biosynthesis in Higher Plants 37
Peter Hedden

2.1 Introduction 37

2.2 Synthesis of ent-kaurene 39

2.2.1 Formation of trans-geranylgeranyl diphosphate 39

2.2.2 Formation of ent-kaurene from trans-geranylgeranyl diphosphate 40

2.3 Reactions catalysed by cytochrome P450 mono-oxygenases 42

2.4 Reactions catalysed by 2-oxoglutarate-dependent dioxygenases 45

2.5 Sites of gibberellin biosynthesis 49

2.6 Regulation of gibberellin biosynthesis 50

2.6.1 Developmental control 50

2.6.2 Gibberellin homoeostasis 51

2.6.3 Regulation by other hormones 54

2.6.4 Regulation by environmental factors 55

2.7 Concluding remarks 59

Acknowledgements 60

References 60

3 Inactivation Processes 73
Hiroshi Magome and Yuji Kamiya

3.1 Introduction 73

3.2 Gibberellin inactivation 75

3.2.1 Gibberellin 2-oxidase 75

3.2.2 Gibberellin methyltransferase 77

3.2.3 Gibberellin 16,17-oxidase 78

3.2.4 Gibberellin 13-oxidase and 12α-oxidase 78

3.2.5 Conjugation with sugar 80

3.3 Regulation of gibberellin inactivation 80

3.3.1 Developmental regulation 81

3.3.2 Gibberellin homoeostasis 82

3.3.3 Regulation by other hormones 83

3.3.4 Environmental regulation 84

3.4 Concluding remarks 87

References 88

4 Gibberellin Transport 95
Jonathan Dayan

4.1 Introduction 95

4.2 Gibberellins can be translocated along plant bodies 96

4.3 Gibberellin transport in seeds 100

4.4 Pattern of gibberellin biosynthesis in transport analysis 101

4.5 Grafting experiments 103

4.6 Significance for secondary growth 104

4.7 Orientation of gibberellin signal flow: source and sink tissues 107

4.8 Monitoring intra- and intercellular gibberellin concentration 110

4.9 Conclusion: new aspects for gibberellin transport 111

4.9.1 Potential transporters 111

4.9.2 Analysis through perception 112

4.9.3 Links to sugar transport 112

Acknowledgements 113

References 114

5 Gibberellins in Fungi, Bacteria and Lower Plants: Biosynthesis, Function and Evolution 121
Bettina Tudzynski, Lena Studt and María Cecilia Rojas

5.1 Introduction 122

5.2 Gibberellin biosynthesis in fungi 122

5.2.1 The biosynthetic pathway in F. fujikuroi: genes and enzymes 122

5.2.2 Gibberellin production in distantly related fungi 126

5.2.3 Evolution of the gibberellin biosynthetic gene cluster in fungi 128

5.2.4 The role of gibberellins in plant infection 131

5.2.5 Strain improvement 132

5.3 Gibberellin biosynthesis in bacteria 133

5.3.1 Free-living rhizobacteria 133

5.3.2 Symbiotic rhizobacteria: genes and reactions of the gibberellin biosynthetic pathway 134

5.3.3 Function and evolution 137

5.4 Gibberellin biosynthesis and signalling components in lower plants 139

5.5 Concluding remarks 143

References 144

6 Gibberellin Hormone Signal Perception: Down-Regulating DELLA Repressors of Plant Growth and Development 153
Sven K. Nelson and Camille M. Steber

6.1 Introduction 154

6.2 DELLA proteins are repressors of gibberellin responses 154

6.3 Gibberellin signalling lifts DELLA repression of gibberellin responses 157

6.4 The gibberellin receptor GID1 (GA-INSENSITIVE DWARF1) 159

6.5 The structural requirements for gibberellin binding by GID1 161

6.6 The structural requirements for the GID1-DELLA protein–protein interaction 162

6.7 The DELLA destruction model: negative regulation of DELLA repressors by SLY1/GID2 and the ubiquitin-proteasome pathway 166

6.8 Regulation of DELLA by phosphorylation and O-GlcNAc modification 169

6.9 Evidence for gibberellin-independent DELLA regulation 173

6.10 Evidence for gibberellin signalling without DELLA destruction 175

6.11 Concluding remarks 177

Acknowledgements 179

References 179

7 DELLA Proteins: Master Regulators of Gibberellin-Responsive Growth and Development 189
Stephen G. Thomas, Miguel A. Blázquez and David Alabadí

7.1 Introduction 190

7.2 DELLAs regulate downstream gibberellin signalling 191

7.3 Gibberellins relieve DELLA-growth repression by targeting their degradation 193

7.4 Functional diversification of DELLA genes 194

7.5 DELLA activity invokes rapid changes in the transcriptome 197

7.6 DELLA proteins activate transcription 198

7.7 DELLAs regulate transcription by physical interaction with transcriptional regulators 199

7.7.1 DELLAs sequester bona fide TFs by physical interaction 200

7.7.2 DELLAs interact with TFs in the context of promoters 204

7.7.3 DELLAs interact with other transcriptional regulators 206

7.7.4 DELLAs regulate chromatin dynamics 208

7.8 A non-genomic response regulated by DELLAs 209

7.9 Analysis of DELLA protein structure-function 210

7.10 GAMYB: A transcriptional regulator of gibberellin responses during cereal grain germination and pollen development 213

7.10.1 GAMYB positively regulates gene expression in cereal aleurone cells 214

7.10.2 GAMYB regulates gibberellin-dependent anther development 216

7.11 Concluding remarks 217

Acknowledgements 218

References 218

8 Interactions Between Gibberellins and other Hormones 229
John J. Ross, Asemeh Miraghazadeh, Amelia H. Beckett, Laura J. Quittenden and Erin L. McAdam

8.1 Introduction 229

8.2 Interactions involving effects of other hormones on gibberellin levels 230

8.2.1 Auxin promotes gibberellin biosynthesis 230

8.2.2 Ethylene inhibits gibberellin biosynthesis 231

8.2.3 Do gibberellin and abscisic acid inhibit each other’s synthesis? 232

8.2.4 Do brassinosteroids act by affecting gibberellin levels? 234

8.2.5 Possible effects of other hormones on gibberellin synthesis 234

8.3 Interactions between hormone signal transduction pathways 234

8.3.1 Do other hormones affect DELLA stability? 235

8.3.2 DELLAs interact with proteins from the signaling pathways of other hormones 237

8.4 Gibberellins and auxin transport 245

8.5 Conclusion 246

Acknowledgements 247

References 247

9 Gibberellins and Seed Germination 253

Terezie Urbanova and Gerhard Leubner-Metzger

9.1 Introduction 254

9.2 Spatiotemporal expression of gibberellin metabolism during Brassicaceae seed germination 254

9.3 Gibberellin signalling and seed germination 264

9.3.1 The GID1ac and GID1b pathways in seeds 264

9.3.2 DELLA proteins and seed germination 268

9.4 Gibberellin and abiotic stress factors: thermoinhibition of seed germination 270

9.5 Gibberellin and biotic stress factors: allelochemical interference of gibberellin biosynthesis during seed germination 273

9.6 Conclusions and perspectives 276

Acknowledgements 277

References 277

10 Gibberellins and Plant Vegetative Growth 285
Cristina Martínez, Ana Espinosa-Ruiz and Salomé Prat

10.1 Introduction 285

10.2 Gibberellins and shoot development 288

10.2.1 Control of SAM function and leaf size 289

10.2.2 Elongation of the hypocotyl 290

10.2.3 Apical hook formation 295

10.3 Gibberellin function in root development 298

10.3.1 Hormonal control of root growth 298

10.3.2 Gibberellin signalling from the endodermis 302

10.3.3 DELLAs downstream signalling in the root 304

10.3.4 DELLAs promote mycorrhizal symbiosis 306

10.4 Growth under unfavourable conditions 308

10.4.1 DELLAs promote resistance to abiotic stress 308

10.4.2 DELLAs and biotic stress 310

10.5 Concluding remarks 311

References 312

11 Gibberellins and Plant Reproduction 323
Andrew R.G. Plackett and Zoe A. Wilson

11.1 Introduction 323

11.2 The floral transition 324

11.2.1 Gibberellin promotes flowering through multiple interacting pathways 324

11.2.2 Sites of gibberellin biosynthesis and action during the floral transition 329

11.2.3 Gibberellin and flowering in perennial species 331

11.3 Floral development 331

11.3.1 Floral patterning and early development 332

11.3.2 Gibberellin and fertility 334

11.4 Seed and fruit development 340

11.4.1 Fruit development 341

11.4.2 Embryo and seed development 345

Acknowledgements 348

References 348

12 Chemical Regulators of Gibberellin Status and their Application in Plant Production 359
Wilhelm Rademacher

12.1 Introduction 359

12.2 Gibberellins 361

12.3 Inhibitors of gibberellin biosynthesis 363

12.3.1 Quaternary ammonium compounds 365

12.3.2 Compounds with a nitrogen-containing heterocycle 366

12.3.3 Structural mimics of 2-oxoglutaric acid 369

12.3.4 16,17-Dihydro-gibberellins 371

12.4 Uses for gibberellins and inhibitors of gibberellin biosynthesis in crop production 372

12.4.1 Wheat, barley, rye, oats and other small-grain cereals 373

12.4.2 Rice 376

12.4.3 Sugarcane 377

12.4.4 Pasture and turf grasses 377

12.4.5 Oilseed rape 379

12.4.6 Cotton 379

12.4.7 Peanuts 381

12.4.8 Opium poppy 382

12.4.9 Fruit trees growing in temperate climate 382

12.4.10 Fruit and nut trees growing in subtropical and tropical climates 385

12.4.11 Grapevines 387

12.4.12 Ornamentals 389

12.4.13 Hybrid seed production 391

12.5 Outlook 391

References 391

13 Genetic Control of Gibberellin Metabolism and Signalling in Crop Improvement 405
Andrew L. Phillips

13.1 Introduction 405

13.2 The REDUCED HEIGHT-1 (Rht-1) alleles of wheat 406

13.2.1 Pleiotropic effects of Rht-1 alleles 410

13.2.2 Rht-1 orthologues in other crop species 412

13.3 The SEMI-DWARF-1(SD-1) alleles of rice 413

13.4 The ELONGATED UPPERMOST INTERNODE (EUI) gene of rice 415

13.5 Commercially useful alleles of other genes from the gibberellin pathway 416

13.6 Transgenic approaches to manipulation of gibberellin-dependent processes in crops 419

13.6.1 Cereals 419

13.6.2 Other crop species 420

13.7 Conclusions 423

Acknowledgements 424

References 424

Appendix The structures of the gibberellins 431

Index 437