title: Gravitropism of Arabidopsis thaliana roots requires the polarization of PIN2 toward the root tip in meristematic cortical cells.
abstract: In the root, the transport of auxin from the tip to the elongation zone, referred to here as shootward, governs gravitropic bending. Shootward polar auxin transport, and hence gravitropism, depends on the polar deployment of the PIN-FORMED auxin efflux carrier PIN2. In Arabidopsis thaliana, PIN2 has the expected shootward localization in epidermis and lateral root cap; however, this carrier is localized toward the root tip (rootward) in cortical cells of the meristem, a deployment whose function is enigmatic. We use pharmacological and genetic tools to cause a shootward relocation of PIN2 in meristematic cortical cells without detectably altering PIN2 polarization in other cell types or PIN1 polarization. This relocation of cortical PIN2 was negatively regulated by the membrane trafficking factor GNOM and by the regulatory A1 subunit of type 2-A protein phosphatase (PP2AA1) but did not require the PINOID protein kinase. When GNOM was inhibited, PINOID abundance increased and PP2AA1 was partially immobilized, indicating both proteins are subject to GNOM-dependent regulation. Shootward PIN2 specifically in the cortex was accompanied by enhanced shootward polar auxin transport and by diminished gravitropism. These results demonstrate that auxin flow in the root cortex is important for optimal gravitropic response.
authors.affiliation: Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, Iwate 020-8550, Japan. abidur@iwate-u.ac.jp
authors.forename: Abidur
authors.initials: A
authors.lastname: Rahman
authors.forename: Maho
authors.initials: M
authors.lastname: Takahashi
authors.forename: Kyohei
authors.initials: K
authors.lastname: Shibasaki
authors.forename: Shuang
authors.initials: S
authors.lastname: Wu
authors.forename: Takehito
authors.initials: T
authors.lastname: Inaba
authors.forename: Seiji
authors.initials: S
authors.lastname: Tsurumi
authors.forename: Tobias I
authors.initials: TI
authors.lastname: Baskin
mesh_terms: D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001692:Biological Transport; D020126:Brefeldin A / Q000494:pharmacology; D018522:Gravitropism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D018519:Meristem / Q000502:physiology*; D018517:Plant Roots / Q000502:physiology*; D054648:Protein Phosphatase 2 / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D020126:Brefeldin A; D020662:Guanine Nucleotide Exchange Factors; D007210:Indoleacetic Acids; D054648:Protein Phosphatase 2; C088087:GNOM protein, Arabidopsis; C117013:AT5G57090 protein, Arabidopsis; C587317:PP2AA1 protein, Arabidopsis