Arabidopsis seedlings display distinct patterns of gene expression and morphogenesis according to the ambient light condition. An Arabidopsis nuclear protein, CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), acts to repress photomorphogenesis in the absence of light. The Arabidopsis CIP7 protein was identified by its capability to interact with COP1. CIP7 is a novel nuclear protein that contains transcriptional activation activity without a recognizable DNA binding motif. CIP7 requires light for its high level of expression, and COP1 seems to play a role in repressing its expression in darkness. Decreasing CIP7 expression by introducing antisense CIP7 RNA resulted in defects in light-dependent anthocyanin and chlorophyll accumulation. Antisense plants also displayed reduced expression of light-inducible genes for anthocyanin biosynthesis and photosynthesis. However, no defect was observed in light-dependent inhibition of hypocotyl elongation. Taken together, our data indicate that CIP7 acts as a positive regulator of light-regulated genes and is a potential direct downstream target of COP1 for mediating light control of gene expression
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