title: Arabidopsis PHYTOCHROME INTERACTING FACTOR proteins promote phytochrome B polyubiquitination by COP1 E3 ligase in the nucleus.
abstract: Many plant photoresponses from germination to shade avoidance are mediated by phytochrome B (phyB). In darkness, phyB exists as the inactive Pr in the cytosol but upon red (R) light treatment, the active Pfr translocates into nuclei to initiate signaling. Degradation of phyB Pfr likely regulates signal termination, but the mechanism is not understood. Here, we show that phyB is stable in darkness, but in R, a fraction of phyB translocates into nuclei and becomes degraded by 26S proteasomes. Nuclear phyB degradation is mediated by COP1 E3 ligase, which preferentially interacts with the PhyB N-terminal region (PhyB-N). PhyB-N polyubiquitination by CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) in vitro can be enhanced by different PHYTOCHROME INTERACTING FACTOR (PIF) proteins that promote COP1/PhyB interaction. Consistent with these results, nuclear phyB accumulates to higher levels in pif single and double mutants and in cop1-4. Our results identify COP1 as an E3 ligase for phyB and other stable phytochromes and uncover the mechanism by which PIFs negatively regulate phyB levels.
authors.affiliation: Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
authors.forename: In-Cheol
authors.initials: IC
authors.lastname: Jang
authors.forename: Rossana
authors.initials: R
authors.lastname: Henriques
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Seo
authors.forename: Akira
authors.initials: A
authors.lastname: Nagatani
authors.forename: Nam-Hai
authors.initials: NH
authors.lastname: Chua
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology*; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D009154:Mutation; D051939:Phytochrome B / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D029681:Arabidopsis Proteins; D051939:Phytochrome B; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases