Ubiquitin- and proteasome-dependent proteolysis in plants.

In recent years it has become obvious that protein degradation is an important catabolic process during development in plants and animals. One very conserved degradative system is the ubiquitin- and proteasome-dependent proteolytic pathway, which is found in all eukaryotes from yeast to mammals and plants. The pathway consists of two parts, one in which chains of ubiquitin are conjugated to substrate proteins, and one in which these substrate proteins are either degraded by the 26S proteasome or are de-ubiquitinated. The ubiquitin- and proteasome-dependent pathway degrades a wide range of proteins in the nucleus and cytoplasm. It is highly specific, but controls a large number of cellular events due to the diversity in the conjugating enzymes. This pathway is important for removal of abnormal/damaged proteins that have had their recognition sites exposed as well as for control of specific transcription factors and cell cycle regulators. In plants, ubiquitin- and proteasome-dependent proteolysis is known to be involved in regulation of the cell cycle and transcription factors as well as endoplasmic reticulum-associated protein degradation, stress response and developmental processes, such as xylogenesis and senescence.