title: Regulation of organ straightening and plant posture by an actin-myosin XI cytoskeleton.
abstract: Plants are able to bend nearly every organ in response to environmental stimuli such as gravity and light(1,2). After this first phase, the responses to stimuli are restrained by an independent mechanism, or even reversed, so that the organ will stop bending and attain its desired posture. This phenomenon of organ straightening has been called autotropism(3) and autostraightening(4) and modelled as proprioception(5). However, the machinery that drives organ straightening and where it occurs are mostly unknown. Here, we show that the straightening of inflorescence stems is regulated by an actin-myosin XI cytoskeleton in specialized immature fibre cells that are parallel to the stem and encircle it in a thin band. Arabidopsis mutants defective in myosin XI (specifically XIf and XIk) or ACTIN8 exhibit hyperbending of stems in response to gravity, an effect independent of the physical properties of the shoots. The actin-myosin XI cytoskeleton enables organs to attain their new position more rapidly than would an oscillating series of diminishing overshoots in environmental stimuli. We propose that the long actin filaments in elongating fibre cells act as a bending tensile sensor to perceive the organ's posture and trigger the straightening system.
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Keishi
authors.initials: K
authors.lastname: Okamoto
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Haruko
authors.initials: H
authors.lastname: Ueda
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma 630-0101, Japan.
authors.forename: Takehide
authors.initials: T
authors.lastname: Kato
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma 630-0101, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Tasaka
authors.affiliation: Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
authors.forename: Miyo Terao
authors.initials: MT
authors.lastname: Morita
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D008841:Actin Cytoskeleton; D017360:Arabidopsis / Q000166:cytology* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018522:Gravitropism / Q000235:genetics; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D018547:Plant Stems / Q000502:physiology; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D008164:Luminescent Proteins; C000602262:myosin XI, Arabidopsis; C054562:yellow fluorescent protein, Bacteria; D009218:Myosins