The Plant Ubiquitin System: From Identification of E2 and E3 enzymes to Molecular Mechanisms and Biological Function

Ubiquitination is an essential post-translation modification involved in almost every cellular process and is critical for proper functioning of eukaryotic cells. The modification involves the covalent attachment of ubiquitin, a small, conserved peptide, to select proteins. One or more ubiquitin molecules may be attached in varying configurations, leading to a range of possible outcomes that regulate protein function, including changes in location, stability, and activity. Components of the ubiquitin system are highly expanded in plants relative to other eukaryotes and play major roles in almost all aspects of plant growth and development, from phytohormone perception and signalling, to maintaining nutrient homeostasis in the face of fluctuating environmental conditions. We begin this Centennial Review by highlighting two Plant Physiology papers that contributed to the identification and characterisation of ubiquitin enzymes. We then provide an update on our understanding of how plants use the ubiquitin system to link environmental change with plant growth and development. We first focus on recent advances in understanding how the structure and function of ubiquitin ligases are modulated by phytohormones and nutrient status. We then highlight emerging knowledge linking components of the ubiquitin system with biomolecular condensates, including stress granules, and discuss the potential functional implications.