title: Arabidopsis SHR and SCR transcription factors and AUX1 auxin influx carrier control the switch between adventitious rooting and xylogenesis in planta and in in vitro cultured thin cell layers.
abstract: OBJECTIVE
  Adventitious roots (ARs) are essential for vegetative propagation. The Arabidopsis thaliana transcription factors SHORT ROOT (SHR) and SCARECROW (SCR) affect primary/lateral root development, but their involvement in AR formation is uncertain. LAX3 and AUX1 auxin influx carriers contribute to primary/lateral root development. LAX3 expression is regulated by SHR, and LAX3 contributes to AR tip auxin maximum. In contrast, AUX1 involvement in AR development is unknown. Xylogenesis is induced by auxin plus cytokinin as is AR formation, but the genes involved are largely unknown. Stem thin cell layers (TCLs) form ARs and undergo xylogenesis under the same auxin plus cytokinin input. The aim of this research was to investigate SHR, SCR, AUX1 and LAX3 involvement in AR formation and xylogenesis in intact hypocotyls and stem TCLs in arabidopsis.
  
  
  METHODS
  Hypocotyls of scr-1, shr-1, lax3, aux1-21 and lax3/aux1-21 Arabidopsis thaliana null mutant seedlings grown with or without auxin plus cytokinin were examined histologically, as were stem TCLs cultured with auxin plus cytokinin. SCR and AUX1 expression was monitored using pSCR::GFP and AUX1::GUS lines, and LAX3 expression and auxin localization during xylogenesis were monitored by using LAX3::GUS and DR5::GUS lines.
  
  
  RESULTS
  AR formation was inhibited in all mutants, except lax3. SCR was expressed in pericycle anticlinally derived AR-forming cells of intact hypocotyls, and in cell clumps forming AR meristemoids of TCLs. The apex was anomalous in shr and scr ARs. In all mutant hypocotyls, the pericycle divided periclinally to produce xylogenesis. Xylary element maturation was favoured by auxin plus cytokinin in shr and aux1-21. Xylogenesis was enhanced in TCLs, and in aux1-21 and shr in particular. AUX1 was expressed before LAX3, i.e. in the early derivatives leading to either ARs or xylogenesis.
  
  
  CONCLUSIONS
  AR formation and xylogenesis are developmental programmes that are inversely related, but they involve fine-tuning by the same proteins, namely SHR, SCR and AUX1. Pericycle activity is central for the equilibrium between xylary development and AR formation in the hypocotyl, with a role for AUX1 in switching between, and balancing of, the two developmental programmes.
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Della Rovere
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Fattorini
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: S
authors.initials: S
authors.lastname: D'Angeli
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Veloccia
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Del Duca
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Cai
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Falasca
authors.affiliation: Department of Environmental Biology, Sapienza University of Rome, Italy, Department of Biological, Geological and Environmental Sciences, University of Bologna, Italy and Department of Life Sciences, University of Siena, Italy mariamaddalena.altamura@uniroma1.it.
authors.forename: M M
authors.initials: MM
authors.lastname: Altamura
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D007701:Kinetin / Q000494:pharmacology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D052584:Xylem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: C100794:AUX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D007211:Indoles; C531125:LAX3 protein, Arabidopsis; D026901:Membrane Transport Proteins; C100978:SCR protein, Arabidopsis; C410510:SHORT ROOT protein, Arabidopsis; D014157:Transcription Factors; C014612:indolebutyric acid; D007701:Kinetin
keywords: AUX1; Adventitious rooting; Arabidopsis thaliana; LAX3; SCR; SHR; auxin influx carriers; thin cell layers; xylogenesis