title: An auxin transport mechanism restricts positive orthogravitropism in lateral roots.
abstract: As soon as a seed germinates, plant growth relates to gravity to ensure that the root penetrates the soil and the shoot expands aerially. Whereas mechanisms of positive and negative orthogravitropism of primary roots and shoots are relatively well understood, lateral organs often show more complex growth behavior. Lateral roots (LRs) seemingly suppress positive gravitropic growth and show a defined gravitropic set-point angle (GSA) that allows radial expansion of the root system (plagiotropism). Despite its eminent importance for root architecture, it so far remains completely unknown how lateral organs partially suppress positive orthogravitropism. Here we show that the phytohormone auxin steers GSA formation and limits positive orthogravitropism in LR. Low and high auxin levels/signaling lead to radial or axial root systems, respectively. At a cellular level, it is the auxin transport-dependent regulation of asymmetric growth in the elongation zone that determines GSA. Our data suggest that strong repression of PIN4/PIN7 and transient PIN3 expression limit auxin redistribution in young LR columella cells. We conclude that PIN activity, by temporally limiting the asymmetric auxin fluxes in the tip of LRs, induces transient, differential growth responses in the elongation zone and, consequently, controls root architecture.
authors.affiliation: Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Vienna (BOKU), Muthgasse 18, 1190 Vienna, Austria.
authors.forename: Michel Ruiz
authors.initials: MR
authors.lastname: Rosquete
authors.forename: Daniel
authors.initials: D
authors.lastname: von Wangenheim
authors.forename: Peter
authors.initials: P
authors.lastname: Marhavý
authors.forename: Elke
authors.initials: E
authors.lastname: Barbez
authors.forename: Ernst H K
authors.initials: EH
authors.lastname: Stelzer
authors.forename: Eva
authors.initials: E
authors.lastname: Benková
authors.forename: Alexis
authors.initials: A
authors.lastname: Maizel
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kleine-Vehn
mesh_terms: D017360:Arabidopsis / Q000254:growth & development / Q000378:metabolism*; D018522:Gravitropism; D007210:Indoleacetic Acids / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D007210:Indoleacetic Acids; D010937:Plant Growth Regulators