title: Missense mutation in the amino terminus of phytochrome A disrupts the nuclear import of the photoreceptor.
abstract: Phytochromes are the red/far-red photoreceptors in higher plants. Among them, phytochrome A (PHYA) is responsible for the far-red high-irradiance response and for the perception of very low amounts of light, initiating the very-low-fluence response. Here, we report a detailed physiological and molecular characterization of the phyA-5 mutant of Arabidopsis (Arabidopsis thaliana), which displays hyposensitivity to continuous low-intensity far-red light and shows reduced very-low-fluence response and high-irradiance response. Red light-induced degradation of the mutant phyA-5 protein appears to be normal, yet higher residual amounts of phyA-5 are detected in seedlings grown under low-intensity far-red light. We show that (1) the phyA-5 mutant harbors a new missense mutation in the PHYA amino-terminal extension domain and that (2) the complex phenotype of the mutant is caused by reduced nuclear import of phyA-5 under low fluences of far-red light. We also demonstrate that impaired nuclear import of phyA-5 is brought about by weakened binding affinity of the mutant photoreceptor to nuclear import facilitators FHY1 (for FAR-RED ELONGATED HYPOCOTYL1) and FHL (for FHY1-LIKE). Finally, we provide evidence that the signaling and degradation kinetics of constitutively nuclear-localized phyA-5 and phyA are identical. Taken together, our data show that aberrant nucleo/cytoplasmic distribution impairs light-induced degradation of this photoreceptor and that the amino-terminal extension domain mediates the formation of the FHY1/FHL/PHYA far-red-absorbing form complex, whereby it plays a role in regulating the nuclear import of phyA.
authors.affiliation: Institute of Plant Biology, Biological Research Centre of the Hungarian Academy of Sciences, H-6701 Szeged, Hungary.
authors.forename: Vladyslava
authors.initials: V
authors.lastname: Sokolova
authors.forename: János
authors.initials: J
authors.lastname: Bindics
authors.forename: Stefan
authors.initials: S
authors.lastname: Kircher
authors.forename: Éva
authors.initials: É
authors.lastname: Ádám
authors.forename: Eberhard
authors.initials: E
authors.lastname: Schäfer
authors.forename: Ferenc
authors.initials: F
authors.lastname: Nagy
authors.forename: András
authors.initials: A
authors.lastname: Viczián
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000235:genetics*; D017360:Arabidopsis / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D008027:Light; D020125:Mutation, Missense; D055519:Photoreceptors, Plant / Q000378:metabolism; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism; D051942:Phytochrome A / Q000235:genetics* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D036226:Seedlings / Q000235:genetics / Q000254:growth & development; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; C524723:FHL protein, Arabidopsis; C441269:FHY1 protein, Arabidopsis; C497973:PHYA protein, Arabidopsis; D055519:Photoreceptors, Plant; D051942:Phytochrome A; D014157:Transcription Factors; D010834:Phytochrome