title: Phyllotaxis and rhizotaxis in Arabidopsis are modified by three PLETHORA transcription factors.
abstract: BACKGROUND
  The juxtaposition of newly formed primordia in the root and shoot differs greatly, but their formation in both contexts depends on local accumulation of the signaling molecule auxin. Whether the spacing of lateral roots along the main root and the arrangement of leaf primordia at the plant apex are controlled by related underlying mechanisms has remained unclear.
  
  
  RESULTS
  Here, we show that, in Arabidopsis thaliana, three transcriptional regulators implicated in phyllotaxis, PLETHORA3 (PLT3), PLT5, and PLT7, are expressed in incipient lateral root primordia where they are required for primordium development and lateral root emergence. Furthermore, all three PLT proteins prevent the formation of primordia close to one another, because, in their absence, successive lateral root primordia are frequently grouped in close longitudinal or radial clusters. The triple plt mutant phenotype is rescued by PLT-vYFP fusion proteins, which are expressed in the shoot meristem as well as the root, but not by expression of PLT7 in the shoot alone. Expression of all three PLT genes requires auxin response factors ARF7 and ARF19, and the reintroduction of PLT activity suffices to rescue lateral root formation in arf7,arf19.
  
  
  CONCLUSIONS
  Intriguingly PLT 3, PLT5, and PLT7 not only control the positioning of organs at the shoot meristem but also in the root; a striking observation that raises many evolutionary questions.
authors.affiliation: Molecular Genetics Group, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Hugo
authors.initials: H
authors.lastname: Hofhuis
authors.forename: Marta
authors.initials: M
authors.lastname: Laskowski
authors.forename: Yujuan
authors.initials: Y
authors.lastname: Du
authors.forename: Kalika
authors.initials: K
authors.lastname: Prasad
authors.forename: Stephen
authors.initials: S
authors.lastname: Grigg
authors.forename: Violaine
authors.initials: V
authors.lastname: Pinon
authors.forename: Ben
authors.initials: B
authors.lastname: Scheres
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C524415:PLT3 protein, Arabidopsis; D014157:Transcription Factors