title: A novel fry1 allele reveals the existence of a mutant phenotype unrelated to 5'->3' exoribonuclease (XRN) activities in Arabidopsis thaliana roots.
abstract: BACKGROUND
  Mutations in the FRY1/SAL1 Arabidopsis locus are highly pleiotropic, affecting drought tolerance, leaf shape and root growth. FRY1 encodes a nucleotide phosphatase that in vitro has inositol polyphosphate 1-phosphatase and 3',(2'),5'-bisphosphate nucleotide phosphatase activities. It is not clear which activity mediates each of the diverse biological functions of FRY1 in planta.
  
  
  RESULTS
  A fry1 mutant was identified in a genetic screen for Arabidopsis mutants deregulated in the expression of Pi High affinity Transporter 1;4 (PHT1;4). Histological analysis revealed that, in roots, FRY1 expression was restricted to the stele and meristems. The fry1 mutant displayed an altered root architecture phenotype and an increased drought tolerance. All of the phenotypes analyzed were complemented with the AHL gene encoding a protein that converts 3'-polyadenosine 5'-phosphate (PAP) into AMP and Pi. PAP is known to inhibit exoribonucleases (XRN) in vitro. Accordingly, an xrn triple mutant with mutations in all three XRNs shared the fry1 drought tolerance and root architecture phenotypes. Interestingly these two traits were also complemented by grafting, revealing that drought tolerance was primarily conferred by the rosette and that the root architecture can be complemented by long-distance regulation derived from leaves. By contrast, PHT1 expression was not altered in xrn mutants or in grafting experiments. Thus, PHT1 up-regulation probably resulted from a local depletion of Pi in the fry1 stele. This hypothesis is supported by the identification of other genes modulated by Pi deficiency in the stele, which are found induced in a fry1 background.
  
  
  CONCLUSIONS
  Our results indicate that the 3',(2'),5'-bisphosphate nucleotide phosphatase activity of FRY1 is involved in long-distance as well as local regulatory activities in roots. The local up-regulation of PHT1 genes transcription in roots likely results from local depletion of Pi and is independent of the XRNs.
authors.affiliation: CEA, DSV IBEB, Laboratoire de Biologie du Développement des Plantes, UMR 6191 CNRS, CEA, Aix-Marseille II, Saint-Paul-lez-Durance, France.
authors.forename: Judith
authors.initials: J
authors.lastname: Hirsch
authors.forename: Julie
authors.initials: J
authors.lastname: Misson
authors.forename: Peter A
authors.initials: PA
authors.lastname: Crisp
authors.forename: Pascale
authors.initials: P
authors.lastname: David
authors.forename: Vincent
authors.initials: V
authors.lastname: Bayle
authors.forename: Gonzalo M
authors.initials: GM
authors.lastname: Estavillo
authors.forename: Hélène
authors.initials: H
authors.lastname: Javot
authors.forename: Serge
authors.initials: S
authors.lastname: Chiarenza
authors.forename: Allison C
authors.initials: AC
authors.lastname: Mallory
authors.forename: Alexis
authors.initials: A
authors.lastname: Maizel
authors.forename: Marie
authors.initials: M
authors.lastname: Declerck
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Pogson
authors.forename: Hervé
authors.initials: H
authors.lastname: Vaucheret
authors.forename: Martin
authors.initials: M
authors.lastname: Crespi
authors.forename: Thierry
authors.initials: T
authors.lastname: Desnos
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Thibaud
authors.forename: Laurent
authors.initials: L
authors.lastname: Nussaume
authors.forename: Elena
authors.initials: E
authors.lastname: Marin
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D017343:Genes, Plant / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000502:physiology; D010641:Phenotype; D028061:Phosphate Transport Proteins / Q000235:genetics / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics*; D018517:Plant Roots / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013217:Starvation / Q000235:genetics / Q000473:pathology
chemical_list: D029681:Arabidopsis Proteins; C494975:PT2 protein, Arabidopsis; D028061:Phosphate Transport Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D005095:Exoribonucleases; C028793:5'-exoribonuclease; D010744:Phosphoric Monoester Hydrolases; C053087:inositol-1,4-bisphosphate 1-phosphatase