ANNUAL PLANT REVIEWS VOLUME 44 -- Contents -- List of Contributors -- Preface -- 1 100 Years of Ethylene - A Personal View -- 1.1 Introduction -- 1.2 Ethylene biosynthesis -- 1.3 Ethylene perception and signalling -- 1.4 Differential responses to ethylene -- 1.5 Ethylene and development -- 1.6 Looking ahead -- Acknowledgements -- References -- 2 Early Events in the Ethylene Biosynthetic Pathway - Regulation of the Pools of Methionine and S-Adenosylmethionine -- 2.1 Introduction -- 2.2 The metabolism of Met and SAM -- 2.3 Regulation of de novo Met synthesis -- 2.4 Regulation of the SAM pool -- 2.4.1 Regulation of SAMS genes by ethylene and of SAMS enzyme activity by protein-S-nitrosylation -- 2.5 The activated methyl cycle -- 2.6 The S-methylmethionine cycle -- 2.7 The methionine or Yang cycle -- 2.7.1 The Yang cycle in relation to polyamine and nicotianamine biosynthesis -- 2.7.2 Regulation of the Yang cycle in relation to ethylene synthesis -- 2.8 Conclusions -- Acknowledgement -- References -- 3 The Formation of ACC and Competition Between Polyamines and Ethylene for SAM -- 3.1 Introduction -- 3.2 Identification and characterization of ACC synthase activity in plants -- 3.2.1 Historical overview -- 3.2.2 Purification and properties of the ACC synthase protein -- 3.3 Analysis of ACC synthase at the transcriptional level -- 3.3.1 Molecular cloning of ACC synthase genes -- 3.3.2 Transcriptional regulation of the ACC synthase gene family -- 3.4 Post-transcriptional regulation of ACS -- 3.4.1 Identification and characterization of interactions with ETO1 -- 3.4.2 Regulation of ACS degradation -- 3.5 Does ACC act as a signal? -- 3.6 Biosynthesis and physiology of polyamines -- 3.6.1 SAM is a substrate for polyamines -- 3.6.2 Physiology of polyamine effects in vitro and in vivo -- 3.6.3 Concurrent biosynthesis of ethylene and polyamines.

3.6.4 Do plant cells invoke a homeostatic regulation of SAM levels? -- Acknowledgements -- References -- 4 The Fate of ACC in Higher Plants -- 4.1 Introduction -- 4.2 History of the discovery of ACC oxidase as the ethylene-forming enzyme -- 4.2.1 Early characterization of ACC oxidase -- 4.2.2 Cloning of the ethylene-forming enzyme as an indicator of enzyme activity -- 4.2.3 Initial biochemical demonstration of ethylene-forming enzyme activity in vitro -- 4.3 Mechanism of the ACC oxidase-catalyzed reaction -- 4.3.1 Investigation of the ACO reaction mechanism -- 4.3.2 Metabolism of HCN -- 4.3.3 Evidence of the conjugation of ACC -- 4.4 Transcriptional regulation of ACC oxidase -- 4.4.1 ACO multi-gene families -- 4.4.2 Differential expression of members of ACO multi-gene families in response to developmental and environmental stimuli -- 4.4.3 Transcriptional regulation of ACO gene expression -- 4.4.4 Crosstalk between ethylene signalling elements and ACO gene expression -- 4.5 Translational regulation of ACC oxidase -- 4.6 Evidence that ACC oxidase acts as a control point in ethylene biosynthesis -- 4.6.1 Cell-specific expression of ACC oxidase -- 4.6.2 Differential expression of ACS and ACO genes -- 4.7 Evolutionary aspects of ACC oxidase -- Acknowledgements -- References -- 5 Perception of Ethylene by Plants - Ethylene Receptors -- 5.1 Historical overview -- 5.2 Subfamilies of ethylene receptors and their evolutionary history -- 5.3 Ethylene binding -- 5.3.1 Requirements for a metal cofactor -- 5.3.2 Characterization of the ethylene-binding pocket and signal transduction -- 5.4 Signal output from the receptors -- 5.5 Overlapping and non-overlapping roles for the receptor isoforms in controlling various phenotypes -- 5.6 Post-translational regulation of the receptors -- 5.6.1 Clustering of receptors -- 5.6.2 Ethylene-mediated degradation of receptors.

5.6.3 Regulatory role of REVERSION-TO-ETHYLENE SENSITIVITY1 (RTE1)/GREEN-RIPE (GR) -- 5.6.4 Other proteins that interact with the ethylene receptors -- 5.7 Conclusions and model -- Acknowledgements -- References -- 6 Ethylene Signalling: the CTR1 Protein Kinase -- 6.1 Introduction -- 6.2 Discovery of CTR1, a negative regulator of ethylene signal transduction -- 6.2.1 Isolation of the Arabidopsis CTR1 mutant -- 6.2.2 CTR1 mutant phenotypes in Arabidopsis -- 6.2.3 Placement of CTR1 in the ethylene-response pathway -- 6.3 CTR1 Encodes a serine/threonine protein kinase -- 6.3.1 Molecular cloning and sequence analysis of the Arabidopsis CTR1 gene -- 6.3.2 CTR1 biochemical activity -- 6.4 The CTR1 gene family -- 6.4.1 The CTR multi-gene family in tomato -- 6.4.2 Functional roles of tomato CTR genes -- 6.4.3 Transcriptional regulation of CTR-like genes -- 6.5 Regulation of CTR1 activity -- 6.5.1 Physical association of CTR1 with ethylene receptors -- 6.5.2 Membrane localization of CTR1 -- 6.5.3 An inhibitory role for the CTR1 N-terminus? -- 6.5.4 Other factors that potentially interact with and regulate CTR1 activity -- 6.6 Elusive targets of CTR1 signalling -- 6.7 CTR1 crosstalk and interactions with other signals -- 6.8 Conclusions -- Acknowledgements -- References -- 7 EIN2 and EIN3 in Ethylene Signalling -- 7.1 Introduction -- 7.2 Overview of ethylene signalling and EIN2 and EIN3 -- 7.3 Genetic identification and biochemical regulation of EIN2 -- 7.4 EIN3 regulation in ethylene signalling -- 7.4.1 Genetic identification and biochemical regulation of EIN3 -- 7.4.2 Structural and functional analysis of ein3 function -- 7.4.3 Function of EIN3 as transcription activator -- 7.5 Functions of ERF1 and other ERFs in ethylene signalling -- 7.6 Future directions -- Acknowledgements -- References -- 8 Ethylene in Seed Development, Dormancy and Germination.

8.1 Introduction -- 8.2 Ethylene in seed embryogenesis -- 8.2.1 Ethylene biosynthesis during zygotic embryogenesis -- 8.2.2 Ethylene involvement in the regulation of seed morphology -- 8.3 Ethylene in seed dormancy and germination -- 8.3.1 Ethylene biosynthesis during dormancy release and germination -- 8.3.2 The role of ethylene in seed heterogeneity -- 8.4 Ethylene interactions with other plant hormones in the regulation of seed dormancy and germination -- 8.5 Ethylene interactions with ROS in the regulation of seed dormancy and germination -- 8.6 Ethylene interactions with other small gaseous signalling molecules (NO, HCN) in the regulation of seed dormancy and germination -- 8.7 Concluding remarks -- Acknowledgements -- References -- 9 The Role of Ethylene in Plant Growth and Development -- 9.1 Introduction -- 9.2 Design of root architecture -- 9.3 Regulation of hypocotyl growth -- 9.4 Shoot architecture and orientation: post-seedling growth -- 9.4.1 Inhibition of growth by ethylene -- 9.4.2 Stimulation of growth by ethylene -- 9.4.3 Shoot gravitropism -- 9.4.4 Control of stomatal density and aperture -- 9.4.5 Activity of the shoot apical meristem -- 9.5 Floral transition -- 9.6 Determination of sexual forms of flowers -- 9.7 Ethylene effects on growth controlling mechanisms -- 9.8 Conclusions -- Acknowledgements -- References -- 10 Ethylene and Cell Separation Processes -- 10.1 Introduction -- 10.2 Overview of the cell separation process -- 10.2.1 Abscission -- 10.2.2 Dehiscence -- 10.2.3 Aerenchyma formation -- 10.2.4 Stomata development and hydathode formation -- 10.2.5 Root cap cell sloughing and lateral root emergence -- 10.2.6 Xylem differentiation -- 10.3 Transcription analyses during cell separation -- 10.4 Relationship between ethylene and other hormones in the regulation of cell separation -- 10.4.1 Ethyene and IAA.

10.4.2 Ethylene and jasmonic acid -- 10.4.3 Ethylene and abscisic acid -- 10.5 Ethylene and signalling systems during cell separation -- 10.5.1 Role of IDA, IDA-like, HAESA and HAESA-like genes -- 10.5.2 MAP kinases -- 10.5.3 Nevershed -- 10.6 Application of knowledge of abscission to crops of horticultural and agricultural importance -- 10.7 Conclusions and future perspectives -- References -- 11 Ethylene and Fruit Ripening -- 11.1 Introduction -- 11.2 Regulation of ethylene production during ripening of climacteric fruit -- 11.2.1 Regulation of ethylene biosynthesis genes during the System 1 to System 2 transition -- 11.2.2 ACS gene alleles are major determinants of ethylene biosynthesis and shelf-life of climacteric fruit -- 11.2.3 Genetic determinism of the climacteric character -- 11.3 Transcriptional control of ethylene biosynthesis genes -- 11.4 Role of ethylene in ripening of non-climacteric fruit -- 11.5 Manipulation of ethylene biosynthesis and ripening -- 11.6 Ethylene-dependent and -independent aspects of climacteric ripening -- 11.7 Ethylene perception and transduction effects in fruit ripening -- 11.7.1 Ethylene perception -- 11.7.2 Chemical control of the post-harvest ethylene response in fruit ripening -- 11.7.3 Ethylene signal transduction -- 11.7.4 The transcriptional cascade leading to the regulation of ethylene-responsive and ripening-related genes -- 11.8 Hormonal crosstalk in fruit ripening -- 11.8.1 Ethylene and abscisic acid -- 11.8.2 Ethylene and jasmonate -- 11.8.3 Ethylene and auxin -- 11.8.4 Ethylene and the gibberellins -- 11.9 Conclusions and future directions -- Acknowledgements -- References -- 12 Ethylene and Senescence Processes -- 12.1 Introduction -- 12.2 Overview of ethylene-mediated senescence in different plant organs -- 12.2.1 Leaf senescence -- 12.2.2 Pod senescence -- 12.2.3 Petal senescence.

12.3 Transcriptional regulation of ethylene-mediated senescence processes.