title: The role of Arabidopsis Actin-Related Protein 3 in amyloplast sedimentation and polar auxin transport in root gravitropism.
abstract: Gravitropism is vital for shaping directional plant growth in response to the forces of gravity. Signals perceived in the gravity-sensing cells can be converted into biochemical signals and transmitted. Sedimentation of amyloplasts in the columella cells triggers asymmetric auxin redistribution in root tips, leading to downward root growth. The actin cytoskeleton is thought to play an important role in root gravitropism, although the molecular mechanism has not been resolved. DISTORTED1 (DIS1) encodes the ARP3 subunit of the Arabidopsis Actin-Related Protein 2/3 (ARP2/3) complex, and the ARP3/DIS1 mutant dis1-1 showed delayed root curvature after gravity stimulation. Microrheological analysis revealed that the high apparent viscosity within dis1-1 central columella cells is closely associated with abnormal movement trajectories of amyloplasts. Analysis using a sensitive auxin input reporter DII-VENUS showed that asymmetric auxin redistribution was reduced in the root tips of dis1-1, and the actin-disrupting drug Latrunculin B increased the asymmetric auxin redistribution. An uptake assay using the membrane-selective dye FM4-64 indicated that endocytosis was decelerated in dis1-1 root epidermal cells. Treatment and wash-out with Brefeldin A, which inhibits protein transport from the endoplasmic reticulum to the Golgi apparatus, showed that cycling of the auxin-transporter PIN-FORMED (PIN) proteins to the plasma membrane was also suppressed in dis1-1 roots. The results reveal that ARP3/DIS1 acts in root gravitropism by affecting amyloplast sedimentation and PIN-mediated polar auxin transport through regulation of PIN protein trafficking.
authors.affiliation: Key Laboratory of Plant Molecular Physiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Jun-Jie
authors.identifier: 0000-0002-4824-400X
authors.initials: JJ
authors.lastname: Zou
authors.affiliation: Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Zhong-Yu
authors.initials: ZY
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Plant Molecular Physiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China.
authors.forename: Shan
authors.initials: S
authors.lastname: Xue
authors.affiliation: Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Han-Hai
authors.initials: HH
authors.lastname: Li
authors.affiliation: Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China lejie@ibcas.ac.cn yurenwang@imech.ac.cn.
authors.forename: Yu-Ren
authors.initials: YR
authors.lastname: Wang
authors.affiliation: Key Laboratory of Plant Molecular Physiology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China lejie@ibcas.ac.cn yurenwang@imech.ac.cn.
authors.forename: Jie
authors.initials: J
authors.lastname: Le
mesh_terms: D051378:Actin-Related Protein 3 / Q000235:genetics / Q000502:physiology*; D000199:Actins / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D018522:Gravitropism / Q000235:genetics / Q000502:physiology*; D007210:Indoleacetic Acids / Q000378:metabolism*; D018613:Microscopy, Confocal; D010937:Plant Growth Regulators / Q000502:physiology*; D018517:Plant Roots / Q000502:physiology*; D018087:Plastids / Q000235:genetics / Q000502:physiology*
chemical_list: D051378:Actin-Related Protein 3; D000199:Actins; D029681:Arabidopsis Proteins; C478027:DIS1 protein, Arabidopsis; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators
keywords: ARP2/3; Amyloplast; PINs.; arabidopsis; auxin; gravitropism