Regulated proteolysis and plant development.

Eukaryotes use the ubiquitin-proteasome system to control the abundance of regulatory proteins such as cell-cycle proteins and transcription factors. Over 5% of the Arabidopsis genome encodes for proteins with an apparent functional homology to components of the ubiquitin-proteasome system. This suggests that ubiquitin-mediated proteolysis has a major role in plant growth and development. Consistent with this notion, various processes, including most phytohormone responses and photomorphogenesis, have already been shown to require protein degradation in one way or another. In this review, we provide an overview of the plant ubiquitin-proteasome system and its role during Arabidopsis development. Since we consider auxin response and photomorphogenesis as particularly instructive examples, these processes are reviewed in greater detail.