title: The Effects of High Steady State Auxin Levels on Root Cell Elongation in Brachypodium.
abstract: The long-standing Acid Growth Theory of plant cell elongation posits that auxin promotes cell elongation by stimulating cell wall acidification and thus expansin action. To date, the paucity of pertinent genetic materials has precluded thorough analysis of the importance of this concept in roots. The recent isolation of mutants of the model grass species Brachypodium distachyon with dramatically enhanced root cell elongation due to increased cellular auxin levels has allowed us to address this question. We found that the primary transcriptomic effect associated with elevated steady state auxin concentration in elongating root cells is upregulation of cell wall remodeling factors, notably expansins, while plant hormone signaling pathways maintain remarkable homeostasis. These changes are specifically accompanied by reduced cell wall arabinogalactan complexity but not by increased proton excretion. On the contrary, we observed a tendency for decreased rather than increased proton extrusion from root elongation zones with higher cellular auxin levels. Moreover, similar to Brachypodium, root cell elongation is, in general, robustly buffered against external pH fluctuation in Arabidopsis thaliana However, forced acidification through artificial proton pump activation inhibits root cell elongation. Thus, the interplay between auxin, proton pump activation, and expansin action may be more flexible in roots than in shoots.
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Pacheco-Villalobos
authors.affiliation: Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, 106 91 Stockholm, Sweden.
authors.forename: Sara M
authors.identifier: 0000-0002-3369-2440
authors.initials: SM
authors.lastname: Díaz-Moreno
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Alja
authors.identifier: 0000-0003-3064-6016
authors.initials: A
authors.lastname: van der Schuren
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tamaki
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Yeon Hee
authors.identifier: 0000-0002-3924-0146
authors.initials: YH
authors.lastname: Kang
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Bojan
authors.initials: B
authors.lastname: Gujas
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden Laboratory of Growth Regulators, Centre of the Region Haná for Biotechnological and Agricultural Research, Institute of Experimental Botany AS CR and Faculty of Science of Palacký University, CZ-78371 Olomouc, Czech Republic.
authors.forename: Ondrej
authors.identifier: 0000-0003-3452-0154
authors.initials: O
authors.lastname: Novak
authors.affiliation: Center for Plant Molecular Biology, Plant Physiology, University of Tübingen, 72074 Tübingen, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Jaspert
authors.affiliation: Centre for Organismal Studies, University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Zhenni
authors.identifier: 0000-0003-1475-2265
authors.initials: Z
authors.lastname: Li
authors.affiliation: Centre for Organismal Studies, University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Sebastian
authors.identifier: 0000-0003-0832-6315
authors.initials: S
authors.lastname: Wolf
authors.affiliation: Center for Plant Molecular Biology, Plant Physiology, University of Tübingen, 72074 Tübingen, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Oecking
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Karin
authors.identifier: 0000-0003-2901-189X
authors.initials: K
authors.lastname: Ljung
authors.affiliation: Division of Glycoscience, School of Biotechnology, Royal Institute of Technology (KTH), AlbaNova University Centre, 106 91 Stockholm, Sweden.
authors.forename: Vincent
authors.initials: V
authors.lastname: Bulone
authors.affiliation: Department of Plant Molecular Biology, University of Lausanne, CH-1015 Lausanne, Switzerland christian.hardtke@unil.ch.
authors.forename: Christian S
authors.initials: CS
authors.lastname: Hardtke
mesh_terms: D058431:Brachypodium / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D005685:Galactans / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D005685:Galactans; D007210:Indoleacetic Acids; C005653:arabinogalactan