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Keywords:

  • degradation;
  • plant;
  • proteasome;
  • signalling;
  • ubiquitin

Contents

 Summary13
I.Brief history13
II.Components of the ubiquitin–proteasome system14
III.Ubiquitin-mediated degradation: a recurrent theme in the plant life cycle18
IV.Conclusion and future prospects25
 Acknowledgements25
 References25

Summary

Ubiquitin is well established as a major modifier of signalling in eukaryotes. However, the extent to which plants rely on ubiquitin for regulating their lifecycle is only recently becoming apparent. This is underlined by the over-representation of genes encoding ubiquitin-metabolizing enzymes in Arabidopsis when compared with other model eukaryotes. The main characteristic of ubiquitination is the conjugation of ubiquitin onto lysine residues of acceptor proteins. In most cases the targeted protein is rapidly degraded by the 26S proteasome, the major proteolysis machinery in eukaryotic cells. The ubiquitin–proteasome system is responsible for removing most abnormal peptides and short-lived cellular regulators, which, in turn, control many processes. This allows cells to respond rapidly to intracellular signals and changing environmental conditions. This review maps out the roles of the components of the ubiquitin–proteasome system with emphasis on areas where future research is urgently needed. We provide a flavour of the diverse aspects of plant lifecycle where the ubiquitin–proteasome system is implicated. We aim to highlight common themes using key examples that reiterate the importance of the ubiquitin–proteasome system to plants. The future challenge in plant biology is to define the targets for ubiquitination, their interactors and their molecular function within the regulatory context.