COP1 and HY5 interact to mediate light-induced gene expression

The plant photomorphogenic mutants hy5 and cop1 have reciprocal phenotypes: hy5 has the long hypocotyl morphology of a dark-grown seedling when grown in the light, whereas cop1 mutants undergo many processes associated with photomorphogenesis, even in the absence of light. The opposing phenotypes of these two mutants extend into general growth characteristics such as lateral root development. The demonstration of a direct molecular interaction between COP1, a repressor of photomorphogenesis localized to the nucleus during the dark, and HY5,(1) a bZIP transcription factor(2) that binds sequence specifically to the light-regulated CHS promoter,(1) provides a possible mechanism by which COP1 transduces light signals to gene expression in Arabidopsis. (C) 1998 John Wiley & Sons, Inc.