title: Gravity-regulated differential auxin transport from columella to lateral root cap cells.
abstract: Gravity-induced root curvature has long been considered to be regulated by differential distribution of the plant hormone auxin. However, the cells establishing these gradients, and the transport mechanisms involved, remain to be identified. Here, we describe a GFP-based auxin biosensor to monitor auxin during Arabidopsis root gravitropism at cellular resolution. We identify elevated auxin levels at the root apex in columella cells, the site of gravity perception, and an asymmetric auxin flux from these cells to the lateral root cap (LRC) and toward the elongation zone after gravistimulation. We differentiate between an efflux-dependent lateral auxin transport from columella to LRC cells, and an efflux- and influx-dependent basipetal transport from the LRC to the elongation zone. We further demonstrate that endogenous gravitropic auxin gradients develop even in the presence of an exogenous source of auxin. Live-cell auxin imaging provides unprecedented insights into gravity-regulated auxin flux at cellular resolution, and strongly suggests that this flux is a prerequisite for root gravitropism.
authors.affiliation: Institut für Biologie II, Universität Freiburg, D-79014 Freiburg, Germany.
authors.forename: Iris
authors.initials: I
authors.lastname: Ottenschläger
authors.forename: Patricia
authors.initials: P
authors.lastname: Wolff
authors.forename: Chris
authors.initials: C
authors.lastname: Wolverton
authors.forename: Rishikesh P
authors.initials: RP
authors.lastname: Bhalerao
authors.forename: Göran
authors.initials: G
authors.lastname: Sandberg
authors.forename: Hideo
authors.initials: H
authors.lastname: Ishikawa
authors.forename: Mike
authors.initials: M
authors.lastname: Evans
authors.forename: Klaus
authors.initials: K
authors.lastname: Palme
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D001692:Biological Transport; D002454:Cell Differentiation; D002455:Cell Division; D006112:Gravitation; D049452:Green Fluorescent Proteins; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008164:Luminescent Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D009154:Mutation; D010937:Plant Growth Regulators / Q000378:metabolism*; D018521:Plant Physiological Phenomena; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism*; D021381:Protein Transport; D015398:Signal Transduction
chemical_list: D007210:Indoleacetic Acids; D008164:Luminescent Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D049452:Green Fluorescent Proteins; C030737:indoleacetic acid