title: Plasma membrane H⁺ -ATPase regulation is required for auxin gradient formation preceding phototropic growth.
abstract: Phototropism is a growth response allowing plants to align their photosynthetic organs toward incoming light and thereby to optimize photosynthetic activity. Formation of a lateral gradient of the phytohormone auxin is a key step to trigger asymmetric growth of the shoot leading to phototropic reorientation. To identify important regulators of auxin gradient formation, we developed an auxin flux model that enabled us to test in silico the impact of different morphological and biophysical parameters on gradient formation, including the contribution of the extracellular space (cell wall) or apoplast. Our model indicates that cell size, cell distributions, and apoplast thickness are all important factors affecting gradient formation. Among all tested variables, regulation of apoplastic pH was the most important to enable the formation of a lateral auxin gradient. To test this prediction, we interfered with the activity of plasma membrane H⁺ -ATPases that are required to control apoplastic pH. Our results show that H⁺ -ATPases are indeed important for the establishment of a lateral auxin gradient and phototropism. Moreover, we show that during phototropism, H⁺ -ATPase activity is regulated by the phototropin photoreceptors, providing a mechanism by which light influences apoplastic pH.
authors.affiliation: Department of Medical Genetics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland Swiss Institute for Bioinformatics, Lausanne, Switzerland.
authors.forename: Tim
authors.initials: T
authors.lastname: Hohm
authors.affiliation: Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Emilie
authors.initials: E
authors.lastname: Demarsy
authors.affiliation: Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Clément
authors.initials: C
authors.lastname: Quan
authors.affiliation: Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Laure
authors.initials: L
authors.lastname: Allenbach Petrolati
authors.affiliation: Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Tobias
authors.initials: T
authors.lastname: Preuten
authors.affiliation: Laboratoire de Reproduction et Développement des Plantes, CNRS INRA ENS Lyon UCBL Université de Lyon, Lyon, France.
authors.forename: Teva
authors.initials: T
authors.lastname: Vernoux
authors.affiliation: Department of Medical Genetics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland Swiss Institute for Bioinformatics, Lausanne, Switzerland sven.bergmann@unil.ch christian.fankhauser@unil.ch.
authors.forename: Sven
authors.initials: S
authors.lastname: Bergmann
authors.affiliation: Centre for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland sven.bergmann@unil.ch christian.fankhauser@unil.ch.
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development*; D002462:Cell Membrane / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000378:metabolism*; D018613:Microscopy, Confocal; D008962:Models, Theoretical; D010766:Phosphorylation; D010788:Photosynthesis; D056949:Phototropins / Q000235:genetics / Q000378:metabolism; D018524:Phototropism; D010834:Phytochrome; D010937:Plant Growth Regulators
chemical_list: D007210:Indoleacetic Acids; D056949:Phototropins; D010937:Plant Growth Regulators; D010834:Phytochrome; D000251:Adenosine Triphosphatases
keywords: auxin; modeling; phototropins; phototropism; plasma membrane H+‐ATPase