Phosphorylation of the Parsley bZIP Transcription Factor CPRF2 Is Regulated by Light

Abstract

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...

The DNA Binding Properties of the Parsley bZIP Transcription Factor CPRF4a Are Regulated by Light

“…Because phosphorylation reactions are frequently involved in the regulation of the intracellular distribution of transcription factors of yeast and animals (11,12), the phosphorylation of CPRF2 might play a role in triggering the nuclear import of the factor. This idea is supported by the fact that the import and the phosphorylation of CPRF2 are both strongly influenced by red light treatment, pointing to an involvement of the red light sensing phytochrome photoreceptors (10).…”

“…DNA Binding Activity of Recombinant CPRF4a after Phosphorylation-The phosphorylation kinetics of recombinant CPRF4a was performed as described previously (10).…”

“…The molecular mechanisms leading to the regulation of the intracellular distribution of CPRF2 are not fully understood. However, we recently described that CPRF2 is phosphorylated in vivo in a light-dependent manner (10). Because phosphorylation reactions are frequently involved in the regulation of the intracellular distribution of transcription factors of yeast and animals (11,12), the phosphorylation of CPRF2 might play a role in triggering the nuclear import of the factor.…”

The α-Helical D1 Domain of the Tobacco bZIP Transcription Factor BZI-1 Interacts with the Ankyrin-repeat Protein ANK1 and Is Important for BZI-1 Function, Both in Auxin Signaling and Pathogen Response

“…The ZIP domain of BZI-1 facilitates specific homo-or heterodimerization (3). Finally, a phosphorylation site has been mapped in the C terminus of the BZI-1-related transcription factor CPRF2 (11).…”

Phylogenetic relationships between Arabidopsis and sugarcane bZIP transcriptional regulatory factors

“…Genetic, molecular and biochemical studies indicate that the bZIP factors of higher plants are important regulators of plant specific processes such as fotomorphogenesis (Osterlund et al, 2000); organ development (Walsh et al, 1997;Chuang et al, 1999); cell elongation and morphogenesis (Yin et al, 1997;Fukazawa et al, 2000); control of nitrogen to carbon balance during seed development (Ciceri et al, 1999); defense mechanisms (Niggeweg et al, 2000;Zhang et al, 1999); sucrose signalling (Rook et al, 1998) and the response to hormones (Choi et al, 2000;Finkelstein et Lynch, 2000;Uno et al, 2000;Niggeweg et al, 2000) and light (Schindler et al, 1992;Wellmer et al, 1999).…”