Nuclear import of the parsley bZIP transcription factor CPRF2 is regulatedby phytochrome photoreceptors

In plants, light perception by photoreceptors leads to differential express ion of an enormous number of genes. An important step for differential gene expression is the regulation of transcription factor activities. To unders tand these processes in light signal transduction we analyzed the three wel l-known members of the common plant regulatory factor (CPRF) family from pa rsley (Petroselinum crispum). Here, we demonstrate that these CPRFs, which belong to the basic-region leucine-zipper (bZIP) domain-containing transcri ption factors, are differentially distributed within parsley cells, indicat ing different regulatory functions within the regulatory networks of the pl ant cell. In particular, we show by cell fractionation and immunolocalizati on approaches that CPRF2 is transported from the cytosol into the nucleus u pon irradiation due to action of phytochrome photoreceptors. Two NH2-termin al domains responsible for cytoplasmic localization of CPRF2 in the dark we re characterized by deletion analysis using a set of CPRF2-green fluorescen t protein (GFP) gene fusion constructs transiently expressed in parsley pro toplasts. We suggest that light-induced nuclear import of CPRF2 is an essen tial step in phytochrome signal transduction.