title: Phytochrome B inhibits binding of phytochrome-interacting factors to their target promoters.
abstract: Phytochromes are red and far-red light receptors in plants that mediate critical responses to light throughout the lifecycle. They achieve this in part by targeting negatively acting bHLH transcription factors called phytochrome-interacting factors (PIFs) for degradation within the nucleus. However, it is not known whether protein degradation is the primary mechanism by which phytochromes inhibit these repressors of photomorphogenesis. Here, we use chromatin immunoprecipitation to show that phyB inhibits the regulatory activity of PIF1 and PIF3 by releasing them from their DNA targets. The N-terminal fragment of phyB (NG-GUS-NLS; NGB) also inhibits binding of PIF3 to its target promoters. However, unlike full-length phyB, NGB does not promote PIF3 degradation, establishing the activity of NGB reflects its ability to inhibit PIF binding to DNA. We further show that Pfr forms of both full-length phyB and NGB inhibit DNA binding of PIF1 and PIF3 in vitro. Taken together, our results indicate that phyB inhibition of PIF function involves two separate processes: sequestration and protein degradation.
authors: Department of Biological Sciences, KAIST, Daejeon 305-701, Korea.
authors: Eunae
authors: E
authors: Park
authors: Jeongmoo
authors: J
authors: Park
authors: Junghyun
authors: J
authors: Kim
authors: Akira
authors: A
authors: Nagatani
authors: J Clark
authors: JC
authors: Lagarias
authors: Giltsu
authors: G
authors: Choi
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D008027:Light; D010766:Phosphorylation; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D025941:Protein Interaction Mapping / Q000379:methods*; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D051939:Phytochrome B; C497952:PHYB protein, Arabidopsis; C508068:At2g20180 protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis