PIF3, a phytochrome-interacting factor necessary for normal photoinduced signal transduction, is a novel basic helix-loop-helix protein.
The mechanism by which the phytochrome (phy) photoreceptor family transduces informational light signals to photoresponsive genes is unknown. Using a yeast two-hybrid screen, we have identified a phytochrome-interacting factor, PIF3, a basic helix-loop-helix protein containing a PAS domain. PIF3 binds to wild-type C-terminal domains of both phyA and phyB, but less strongly to signaling-defective, missense mutant-containing domains. Expression of sense or antisense PIF3 sequences in transgenic Arabidopsis perturbs photoresponsiveness in a manner indicating that PIF3 functions in both phyA and phyB signaling pathways in vivo. PIF3 localized to the nucleus in transient transfection experiments, indicating a potential role in controlling gene expression. Together, the data suggest that phytochrome signaling to photoregulated genes includes a direct pathway involving physical interaction between the photoreceptor and a transcriptional regulator.
Ni
M
M
Department of Plant and Microbial Biology, University of California, Berkeley 94720, USA.
Tepperman
J M
JM
Quail
P H
PH
D017360:Arabidopsis / Q000737:chemistry; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D002467:Cell Nucleus / Q000378:metabolism; D018744:DNA, Plant / Q000737:chemistry; D018257:Helix-Loop-Helix Motifs / Q000502:physiology*; D008969:Molecular Sequence Data; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D010786:Photoreceptor Cells; D010834:Phytochrome / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051942:Phytochrome A; D051939:Phytochrome B; D030821:Plants, Genetically Modified; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors; D014162:Transfection; D015003:Yeasts
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D018744:DNA, Plant; D016376:Oligonucleotides, Antisense; D010834:Phytochrome; D051942:Phytochrome A; D051939:Phytochrome B; D014157:Transcription Factors; C497973:PHYA protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis