In plants, light perception by photoreceptors leads to differential expression of an enormous number of genes. An important step for differential gene expression is the regulation of transcription factor activities. To understand these processes in light signal transduction we analyzed the three well-known members of the common plant regulatory factor (CPRF) family from parsley (Petroselinum crispum). Here, we demonstrate that these CPRFs, which belong to the basic- region leucine-zipper (bZIP) domain-containing transcription factors, are differentially distributed within parsley cells, indicating different regulatory functions within the regulatory networks of the plant cell. In particular, we show by cell fractionation and immunolocalization approaches that CPRF2 is transported from the cytosol into the nucleus upon irradiation due to action of phytochrome photoreceptors. Two NH2-terminal domains responsible for cytoplasmic localization of CPRF2 in the dark were characterized by deletion analysis using a set of CPRF2-green fluorescent protein (GFP) gene fusion constructs transiently expressed in parsley protoplasts. We suggest that light-induced nuclear import of CPRF2 is an essential step in phytochrome signal transduction.

The analysis of the complex network of signal transduction chains has demonstrated the importance of transcription factor activities for the control of gene expression. To understand how transcription factor activities in plants are regulated in response to light, we analyzed the common plant regulatory factor 2 (CPRF2) from parsley (Petroselinum crispum L.) that interacts with promoter elements of light-regulated genes. Here, we demonstrate that CPRF2 is a phosphoprotein in vivo and that its phosphorylation state is rapidly increased in response to light. Phosphorylation in vitro as well as in vivo occurs primarily within the C-terminal half of the factor, and is caused by a cytosolic 40-kDa protein serine kinase. In contrast to other plant basic leucinezipper motif factors, phosphorylation of CPRF2 does not alter its DNA binding activity. Therefore, we discuss alternative functions of the light-dependent phosphorylation of CPRF2 including the regulation of its nucleocytoplasmic partitioning.Light is probably the most variable environmental factor controlling plant development. To monitor light quality and quantity, plants have evolved at least three different photoreceptor systems: the red/far-red reversible phytochromes, the blue/UV-A, and the UV-B photoreceptors (1). The most well understood of these photoreceptors is the phytochrome system (2, 3).Besides the search for appropriate mutants, other approaches have been used to understand the signal transduction mechanisms mediated by photoreceptors. (i) Characterizing the photoreceptors themselves and searching for interacting proteins, (ii) unraveling the role of signal mediators like Ca 2ϩ , calmodulin, cGMP, and phosphorylation events (4), and (iii) analyzing DNA-binding proteins that interact with promoter elements of light-regulated genes. As shown, for example, for chalcone synthase or chlorophyll a/b-binding protein genes, promoter elements that mediate light responsiveness frequently contain the palindromic DNA motif ACGT, that, depending on the adjacent nucleotides, is part of the so-called G-box (CACGTG) or C-box (GACGTC) sequences (5). However, G-and C-boxes are not only found in the promoters of lightregulated genes but also in promoters of genes that respond to other exogenic and endogenic stimuli such as stress, hormones, and cell cycle-related signals (6). Transcription factors containing a basic leucine-zipper motif (bZIP), 1 as, for example, the common plant regulatory factors (CPRFs) from parsley (7-11) and G-box binding factors from Arabidopsis (12-14), were shown to bind to the G-box or the C-box, respectively, in vitro as well as in vivo and form specific homo-and heterodimers (7,8,12,13). Since CPRF and G-box binding factors proteins, which have molecular masses between 35 and 45 kDa, are encoded by multigene families (15), it is difficult to define which and how many members directly act as transcription factors regulating a certain inducible gene.The regulation of the activities of these factors in response to light is poorly understood...

Developing shoots of grapevine ( Vitis vinifera cv. Kerner) were inoculated with conidia of the powdery mildew, Uncinula necator , at well-defined phenological stages of the host to provoke the development of flag shoots in the field and to investigate these shoots as early as possible in the following growing season for the presence of the pathogen. The disease progress was monitored and fungal growth and development on samples from a field trial were analysed by means of low-temperature scanning electron microscopy (LT-SEM). Mycelium was detected on the surface and in the interior parts of buds. The suitability of the field plot to analyse flag shoots was proven by the occurrence of such shoots in the following spring. Furthermore, early stages of cleistothecia development on berries were described for the first time. Establishment of U. necator in dormant buds of grapevine, giving rise to flag shoots in the following spring, is considered to play a significant role in overwintering of the pathogen in the vineyards of southern Germany.

The common plant regulatory factors (CPRFs) from parsley are transcription factors with a basic-leucine-zipper motif that bind to cis-regulatory elements frequently found in promoters of light-regulated genes. Proposed to function in concert with members of other transcription factor families, CPRFs regulate the transcriptional activity of many target genes. Here, we report that, in contrast to CPRF2, which operates as a transcriptional activator, CPRF1 functions as repressor in vivo. Two-hybrid screens using CPRF1 and CPRF2 as "baits" resulted in the isolation of four novel parsley proteins which interact with either CPRF1 or CPRF2 in vivo. Three of these factors represent new parsley bZIP factors, designated CPRF5-CPRF7, whereas the fourth, named CPRF1-interacting protein (CIP), shows no homology to any other known protein. CPRF5 and CIP specifically interact with CPRF1, whilst CPRF6 and CPRF7 exclusively form heterodimers with CPRF2. CPRF5, CPRF6 and CPRF7 are transcription factors that exhibit sequence-specific DNA-binding as well as transactivation abilities, whereas the function of CIP remains elusive. The newly isolated CPRFs and CIP are constitutively localized in the nucleus in parsley protoplasts. Furthermore, mRNA accumulation studies revealed that the expression of these novel bZIP genes and CIP is not altered by exposure to light. We discuss the possible roles of the newly identified proteins in CPRF1- and CPRF2-dependent target gene expression.