Structural organization and interactions of COP1, a light-regulated developmental switch.

Arabidopsis seedling development follows contrasting patterns depending on ambient light conditions, photomorphogenesis in the light and skotomorphogenesis or etiolation in darkness. COP1 is a limiting or regulatory component in mediating repression of photomorphogenesis in the absence of light. COP1 acts within the nucleus in the dark, directly interacts and regulates specific transcription factors that are required for promoting photomorphogenesis. Light abrogates COP1 action and results in progressive nuclear depletion of COP1 with increasing light stimuli. COP1 contains multiple structural modules, which are responsible for interacting with distinct cellular factors and play specific functional roles. We review the most recent progress in understanding the COP1 action and propose specific models based on the recent studies.