title: OWL1: an Arabidopsis J-domain protein involved in perception of very low light fluences.
abstract: To sense ambient light conditions in order to optimize their growth and development, plants employ a battery of photoreceptors responsive to light quality and quantity. Essential for the sensing of red and far-red (FR) light is the phytochrome family of photoreceptors. Among them, phytochrome A is special because it mediates responses to different light conditions, including both very low fluences (very low fluence response [VLFR]) and high irradiances (high irradiance response [HIR]). In contrast with the FR-HIR signaling pathway, in which several intermediates of the signaling pathway have been identified, specific components of the VLFR pathway remain unknown. Here, we describe owl1 (for orientation under very low fluences of light), a mutant that is specific for the VLFR, suggesting that VLFR and HIR pathways are genetically distinct, although some common mechanisms can be observed. OWL1 codes for a ubiquitous J-domain protein essential for germination, cotyledon opening, hypocotyl elongation, and deviation of the direction of hypocotyl growth from the vertical under very low light conditions. Additionally, we observed a flowering phenotype suggesting a role for the VLFR during the whole life cycle of a plant. OWL1 interacts with the basic helix-loop-helix HFR1 (LONG HYPOCOTYL IN FAR-RED) transcription factor, previously characterized as a component of the FR-HIR pathway. Both proteins are involved in the agravitropic response under FR light. We propose a central function of OWL1 in the VLFR pathway, which is essential for plant survival under unfavorable light conditions.
authors.affiliation: Institute of Botany, Department for Biology I, Ludwig-Maximilians-Universität, 82152 Planegg-Martinsried, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Kneissl
authors.forename: Volker
authors.initials: V
authors.lastname: Wachtler
authors.forename: Nam-Hai
authors.initials: NH
authors.lastname: Chua
authors.forename: Cordelia
authors.initials: C
authors.lastname: Bolle
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D035264:Flowers / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000528:radiation effects; D015151:Immunoblotting; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018547:Plant Stems / Q000378:metabolism; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000528:radiation effects; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C414438:At1g02340 protein, Arabidopsis