Arabidopsis PHYTOCHROME INTERACTING FACTOR proteins promote phytochrome B polyubiquitination by COP1 E3 ligase in the nucleus.
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.
Jang
In-Cheol
IC
Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10065, USA.
Henriques
Rossana
R
Seo
Hak Soo
HS
Nagatani
Akira
A
Chua
Nam-Hai
NH
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
D029681:Arabidopsis Proteins; D051939:Phytochrome B; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases