THE PLANT CELL, Vol 6, Issue 10 1391-1400, Copyright © 1994 by American Society of Plant Biologists
Overexpression of Arabidopsis COP1 Results in Partial Suppression of Light-Mediated Development: Evidence for a Light-Inactivable Repressor of Photomorphogenesis
T. W. McNellis, AGv. Arnim and X. W. Deng
Department of Biology, Yale University, New Haven, Connecticut 06520-8104
Arabidopsis seedlings are genetically endowed with the capability to follow
two distinct developmental programs: photomorphogenesis in the light and
skotomorphogenesis in darkness. The regulatory protein CONSTITUTIVE
PHOTOMORPHOGENIC1 (COP1) has been postulated to act as a repressor of
photomorphogenesis in the dark because loss-of-function mutations of COP1
result in dark-grown seedlings phenocopying the light-grown wild-type
seedlings. In this study, we tested this working model by overexpressing
COP1 in the plant and examining its inhibitory effects on photomorphogenic
development. Stable transgenic Arabidopsis lines overexpressing COP1 were
generated through Agrobacterium-mediated transformation. Overexpression was
achieved using either the strong cauliflower mosaic virus 35S RNA promoter
or additional copies of the wild-type gene. Analysis of these transgenic
lines demonstrated that higher levels of COP1 can inhibit aspects of
photomorphogenic seedling development mediated by either phytochromes or a
blue light receptor, and the extent of inhibition correlated quantitatively
with the in vivo COP1 levels. This result provides direct evidence that
COP1 acts as a molecular repressor of photomorphogenic development and that
multiple photoreceptors can independently mediate the light inactivation of
COP1. It also suggests that a controlled inactivation of COP1 may provide a
basis for the ability of plants to respond quantitatively to changing light
signals, such as fluence rate and photoperiod.
