title: Targeted knockout in Physcomitrella reveals direct actions of phytochrome in the cytoplasm.
abstract: The plant photoreceptor phytochrome plays an important role in the nucleus as a regulator of transcription. Numerous studies imply, however, that phytochromes in both higher and lower plants mediate physiological reactions within the cytoplasm. In particular, the tip cells of moss protonemal filaments use phytochrome to sense light direction, requiring a signaling system that transmits the directional information directly to the microfilaments that direct tip growth. In this work we describe four canonical phytochrome genes in the model moss species Physcomitrella patens, each of which was successfully targeted via homologous recombination and the distinct physiological functions of each gene product thereby identified. One homolog in particular mediates positive phototropism, polarotropism, and chloroplast movement in polarized light. This photoreceptor thus interacts with a cytoplasmic signal/response system. This is our first step in elucidating the cytoplasmic signaling function of phytochrome at the molecular level.
authors.affiliation: Pflanzenphysiologie, Justus Liebig Universität Giessen, Senckenbergstrasse 3, D35390 Giessen, Germany. franz.mittmann@bot3.bio.uni-giessen.de
authors.forename: Franz
authors.initials: F
authors.lastname: Mittmann
authors.forename: Gerhard
authors.initials: G
authors.lastname: Brücker
authors.forename: Mathias
authors.initials: M
authors.lastname: Zeidler
authors.forename: Alexander
authors.initials: A
authors.lastname: Repp
authors.forename: Thomas
authors.initials: T
authors.lastname: Abts
authors.forename: Elmar
authors.initials: E
authors.lastname: Hartmann
authors.forename: Jon
authors.initials: J
authors.lastname: Hughes
mesh_terms: D001483:Base Sequence; D019068:Bryopsida / Q000145:classification / Q000235:genetics*; D003593:Cytoplasm / Q000502:physiology; D017931:DNA Primers; D017353:Gene Deletion; D008954:Models, Biological; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D010834:Phytochrome / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D010834:Phytochrome