title: Interaction with plant transcription factors can mediate nuclear import of phytochrome B.
abstract: Phytochromes (phy) are red/far-red-absorbing photoreceptors that regulate the adaption of plant growth and development to changes in ambient light conditions. The nuclear transport of the phytochromes upon light activation is regarded as a key step in phytochrome signaling. Although nuclear import of phyA is regulated by the transport facilitators far red elongated hypocotyl 1 (FHY1) and fhy1-like, an intrinsic nuclear localization signal was proposed to be involved in the nuclear accumulation of phyB. We recently showed that nuclear import of phytochromes can be analyzed in a cell-free system consisting of isolated nuclei of the unicellular green algae Acetabularia acetabulum. We now show that this system is also versatile to elucidate the mechanism of the nuclear transport of phyB. We tested the nuclear transport characteristics of full-length phyB as well as N- and C-terminal phyB fragments in vitro and showed that the nuclear import of phyB can be facilitated by phytochrome-interacting factor 3 (PIF3). In vivo measurements of phyB nuclear accumulation in the absence of PIF1, -3, -4, and -5 indicate that these PIFs are the major transport facilitators during the first hours of deetiolation. Under prolonged irradiations additional factors might be responsible for phyB nuclear transport in the plant.
authors.affiliation: Plant Physiology, Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany. pfeiffer@berkeley.edu
authors.forename: Anne
authors.initials: A
authors.lastname: Pfeiffer
authors.forename: Marie-Kristin
authors.initials: MK
authors.lastname: Nagel
authors.forename: Claudia
authors.initials: C
authors.lastname: Popp
authors.forename: Florian
authors.initials: F
authors.lastname: Wüst
authors.forename: János
authors.initials: J
authors.lastname: Bindics
authors.forename: András
authors.initials: A
authors.lastname: Viczián
authors.forename: Andreas
authors.initials: A
authors.lastname: Hiltbrunner
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
authors.forename: Tim
authors.initials: T
authors.lastname: Kunkel
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schäfer
mesh_terms: D000076:Acetabularia / Q000378:metabolism; D021581:Active Transport, Cell Nucleus; D017360:Arabidopsis / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D019913:Nuclear Localization Signals; D051939:Phytochrome B / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D019913:Nuclear Localization Signals; D051939:Phytochrome B; D011993:Recombinant Fusion Proteins; C497952:PHYB protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis