Phosphorylation by CK2 Enhances the Rapid Light-induced Degradation of Phytochrome Interacting Factor 1 in Arabidopsis

• Published in: The Journal of biological chemistry Vol. 286; no. 14; pp. 12066 - 12074
• Main Authors: Bu, Qingyun, Zhu, Ling, Dennis, Michael D., Yu, Lu, Lu, Sheen X., Person, Maria D., Tobin, Elaine M., Browning, Karen S., Huq, Enamul
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08.04.2011; American Society for Biochemistry and Molecular Biology
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - radiation effects; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; bHLH Factor; Blotting, Western; Casein Kinase II - genetics; Casein Kinase II - metabolism; CK2; Gene Expression Regulation, Plant; Helix-Loop-Helix Transcription Factors; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Light; Phosphoproteins - genetics; Phosphoproteins - metabolism; Phosphorylation; Photomorphogenesis; Plant Biology; Plant Proteins - genetics; Plant Proteins - metabolism; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - radiation effects; Posttranslational Modification; Proteasomal Degradation; Protein Degradation; Protein Phosphorylation; Ubiquitination; Helix-Loop-Helix Transcription Factors; Ubiquitination; Phosphorylation; bHLH Factor; Proteasomal Degradation; Protein Phosphorylation; CK2; Posttranslational Modification; Protein Degradation; Photomorphogenesis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.186882

The phytochrome family of sensory photoreceptors interacts with phytochrome interacting factors (PIFs), repressors of photomorphogenesis, in response to environmental light signals and induces rapid phosphorylation and degradation of PIFs to promote photomorphogenesis. However, the kinase that phosphorylates PIFs is still unknown. Here we show that CK2 directly phosphorylates PIF1 at multiple sites. α1 and α2 subunits individually phosphorylated PIF1 weakly in vitro. However, each of four β subunits strongly stimulated phosphorylation of PIF1 by α1 or α2. Mapping of the phosphorylation sites identified seven Ser/Thr residues scattered throughout PIF1. Ser/Thr to Ala scanning mutations at all seven sites eliminated CK2-mediated phosphorylation of PIF1 in vitro. Moreover, the rate of degradation of the Ser/Thr to Ala mutant PIF1 was significantly reduced compared with wild-type PIF1 in transgenic plants. In addition, hypocotyl lengths of the mutant PIF1 transgenic plants were much longer than the wild-type PIF1 transgenic plants under light, suggesting that the mutant PIF1 is suppressing photomorphogenesis. Taken together, these data suggest that CK2-mediated phosphorylation enhances the light-induced degradation of PIF1 to promote photomorphogenesis.