title: Identification and functional characterization of phytosulfokine receptor using a ligand-based approach.
abstract: Almost all plant cells, even when fully differentiated, can dedifferentiate and proliferate in vitro to form a callus, in which they can then differentiate to form various organs. These sequential processes can be promoted by exposing the cells to a conditioned medium in which either the same or other cells have previously been grown, indicating the involvement of cell-to-cell communication mediated by a chemical factor. This factor was purified from the conditioned medium and identified as a 5-amino-acid sulfated peptide. The addition of this peptide, named phytosulfokine (PSK), to the culture medium, even at nanomolar concentrations, significantly promotes cellular proliferation and/or cellular differentiation. We purified a membrane receptor for PSK (PSKR1) by ligand-based affinity chromatography and identified it as a member of leucine-rich repeat receptor kinases. The PSK-binding domain of PSKR1 was further identified by ligand photoaffinity labeling using a novel "on-column photoaffinity labeling" methodology that allows repeated incorporation of the photoaffinity label. Analysis of loss-of-function and gain-of-function mutants of the Arabidopsis PSKR1 revealed that PSK signaling affects cellular longevity and potential for growth without interfering with basic plant morphogenesis. These results suggest that PSK represents a new class of hormones that affect the potential for cellular growth and longevity of individual cells via binding to PSKR1, thereby exerting a pleiotropic effect on individual cells in response to environmental conditions.
authors.affiliation: Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan. matsu@agr.nagoya-u.ac.jp
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Matsubayashi
authors.forename: Hidefumi
authors.initials: H
authors.lastname: Shinohara
authors.forename: Mari
authors.initials: M
authors.lastname: Ogawa
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001665:Binding Sites; D049109:Cell Proliferation; D008024:Ligands; D008969:Molecular Sequence Data; D019920:Photoaffinity Labels; D010937:Plant Growth Regulators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016415:Sequence Alignment; D015398:Signal Transduction; D019076:Transgenes
chemical_list: D029681:Arabidopsis Proteins; D008024:Ligands; C515018:PSKR1 protein, Arabidopsis; D019920:Photoaffinity Labels; D010937:Plant Growth Regulators; D011956:Receptors, Cell Surface