title: Nuclear accumulation of the phytochrome A photoreceptor requires FHY1.
abstract: The phytochrome family of red/far-red (R/FR)-responsive photoreceptors plays a key role throughout the life cycle of plants . Arabidopsis has five phytochromes, phyA-phyE, among which phyA and phyB play the most predominant functions . Light-regulated nuclear accumulation of the phytochromes is an important regulatory step of this pathway, but to this date no factor specifically required for this event has been identified . Among all phyA signaling mutants, fhy1 and fhy3 (far-red elongated hypocotyl 1 and 3) have the most severe hyposensitive phenotype, indicating that they play particularly important roles . FHY1 is a small plant-specific protein of unknown function localized both in the nucleus and the cytoplasm . Here we show that FHY1 is specifically required for the light-regulated nuclear accumulation of phyA but not phyB. Moreover, phyA accumulation is only slightly affected in fhy3, indicating that the diminished nuclear accumulation of phyA observed in fhy1 seedlings is not simply a general consequence of reduced phyA signaling. By in vitro pull-down and yeast two-hybrid analyses, we demonstrate that FHY1 physically interacts with phyA, preferentially in its active Pfr form. Furthermore, FHY1 and phyA colocalize in planta. We therefore identify the first component required for light-regulated phytochrome nuclear accumulation.
authors.affiliation: Institut für Biologie II/Botanik, Albert Ludwigs Universität, Schänzlestrasse 1, D-79104 Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hiltbrunner
authors.forename: András
authors.initials: A
authors.lastname: Viczián
authors.forename: Erik
authors.initials: E
authors.lastname: Bury
authors.forename: Anke
authors.initials: A
authors.lastname: Tscheuschler
authors.forename: Stefan
authors.initials: S
authors.lastname: Kircher
authors.forename: Réka
authors.initials: R
authors.lastname: Tóth
authors.forename: Ariane
authors.initials: A
authors.lastname: Honsberger
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schäfer
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D017931:DNA Primers; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008027:Light; D008856:Microscopy, Fluorescence; D010834:Phytochrome / Q000378:metabolism*; D051942:Phytochrome A / Q000378:metabolism*; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; C441269:FHY1 protein, Arabidopsis; D051942:Phytochrome A; D010834:Phytochrome; D049452:Green Fluorescent Proteins