Phytochrome B inhibits binding of phytochrome‐interacting factors to their target promoters

• Published in: The Plant journal : for cell and molecular biology Vol. 72; no. 4; pp. 537 - 546
• Main Authors: Park, Eunae, Park, Jeongmoo, Kim, Junghyun, Nagatani, Akira, Lagarias, J. Clark, Choi, Giltsu
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.11.2012; Blackwell
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - radiation effects; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; basic helix-loop-helix transcription factors; Basic Helix-Loop-Helix Transcription Factors - genetics; Basic Helix-Loop-Helix Transcription Factors - metabolism; Biological and medical sciences; Cell Nucleus - genetics; Cell Nucleus - metabolism; Chromatin; Chromatin Immunoprecipitation; degradation; Deoxyribonucleic acid; DNA; DNA binding; Fundamental and applied biological sciences. Psychology; Light; Phosphorylation; phytochrome; Phytochrome B - genetics; Phytochrome B - metabolism; phytochrome‐interacting factors 1; phytochrome‐interacting factors 3; Plant biology; Plant physiology and development; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - radiation effects; Promoter Regions, Genetic; Protein Binding; protein degradation; Protein Interaction Mapping - methods; Protein Stability; Protein Structure, Tertiary; Proteins; Proteolysis; receptors; Transcription, Genetic; Degradation; Binding; Promoter; Target; Phosphorylation; DNA; Phytochrome; phytochrome-interacting factors 1; Inhibition; DNA binding; phytochrome-interacting factors 3
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2012.05114.x

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.