title: Photoactivated phytochrome induces rapid PIF3 phosphorylation prior to proteasome-mediated degradation.
abstract: Following light-induced nuclear translocation, specific members of the phytochrome (phy) photoreceptor family (phyA to phyE) interact with bHLH transcription factors, such as PIF3, and induce changes in target-gene expression. The biochemical mechanism comprising signal transfer from phy to PIF3 has remained undefined but results in rapid degradation of PIF3. We provide evidence that photoactivation of phy induces rapid in vivo phosphorylation of PIF3 preceding degradation. Both phyA and phyB redundantly induce this PIF3 phosphorylation, as well as nuclear speckle formation and degradation, by direct interaction with PIF3 via separate binding sites. These data suggest that phy-induced phosphorylation of proteins such as PIF3 may represent the primary intermolecular signaling transaction of the activated photoreceptor, tagging the target protein for proteosomal degradation, possibly in nuclear speckles.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, California 94720, USA.
authors.forename: Bassem
authors.initials: B
authors.lastname: Al-Sady
authors.forename: Weimin
authors.initials: W
authors.lastname: Ni
authors.forename: Stefan
authors.initials: S
authors.lastname: Kircher
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schäfer
authors.forename: Peter H
authors.initials: PH
authors.lastname: Quail
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000469:Alkaline Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D001059:Apoproteins / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D007976:Leupeptins / Q000494:pharmacology; D008027:Light; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism*; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011485:Protein Binding; D020798:Two-Hybrid System Techniques
chemical_list: D000469:Alkaline Phosphatase; D001059:Apoproteins; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D007976:Leupeptins; D010834:Phytochrome; D051942:Phytochrome A; D051939:Phytochrome B; D011480:Protease Inhibitors; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; C116162:PIF3 protein, Arabidopsis; C088754:PHYD protein, Arabidopsis; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde