The ubiquitin/26S proteasome pathway, the complex last chapter in the life of many plant proteins.

Plants use a repertoire of methods to control the level and activity of their constituent proteins. One method, whose prominence is only now being appreciated, is selective protein breakdown by the ubiquitin/26S proteasome pathway. Remarkably, recent analyses of the near-complete Arabidopsis thaliana genome identified >1300 genes, or approximately 5% of the proteome, involved in the ubiquitin/26S proteasome pathway, making it one of the most elaborate regulatory mechanisms in plants. Molecular genetic analyses have also connected individual components to almost all aspects of plant biology, including the cell-cycle, embryogenesis, photomorphogenesis, circadian rhythms, hormone signaling, homeosis, disease resistance and senescence. Consequently, it appears that the ubiquitin/26S proteasome pathway rivals transcription complexes and protein kinase cascades as the main player in plant cell regulation.