title: ULTRAPETALA1 and LEAFY pathways function independently in specifying identity and determinacy at the Arabidopsis floral meristem.
abstract: OBJECTIVE
  The morphological variability of the flower in angiosperms, combined with its relatively simple structure, makes it an excellent model to study cell specification and the establishment of morphogenetic patterns. Flowers are the products of floral meristems, which are determinate structures that generate four different types of floral organs before terminating. The precise organization of the flower in whorls, each defined by the identity and number of organs it contains, is controlled by a multi-layered network involving numerous transcriptional regulators. In particular, the AGAMOUS (AG) MADS domain-containing transcription factor plays a major role in controlling floral determinacy in Arabidopsis thaliana in addition to specifying reproductive organ identity. This study aims to characterize the genetic interactions between the ULTRAPETALA1 (ULT1) and LEAFY (LFY) transcriptional regulators during flower morphogenesis, with a focus on AG regulation.
  
  
  METHODS
  Genetic and molecular approaches were used to address the question of redundancy and reciprocal interdependency for the establishment of flower meristem initiation, identity and termination. In particular, the effects of loss of both ULT1 and LFY function were determined by analysing flower developmental phenotypes of double-mutant plants. The dependency of each factor on the other for activating developmental genes was also investigated in gain-of-function experiments.
  
  
  RESULTS
  The ULT1 and LFY pathways, while both activating AG expression in the centre of the flower meristem, functioned independently in floral meristem determinacy. Ectopic transcriptional activation by ULT1 of AG and AP3, another gene encoding a MADS domain-containing flower architect, did not depend on LFY function. Similarly, LFY did not require ULT1 function to ectopically determine floral fate.
  
  
  CONCLUSIONS
  The results indicate that the ULT1 and LFY pathways act separately in regulating identity and determinacy at the floral meristem. In particular, they independently induce AG expression in the centre of the flower to terminate meristem activity. A model is proposed whereby these independent contributions bring about a switch at the AG locus from an inactive to an active transcriptional state at the correct time and place during flower development.
authors.affiliation: Université Grenoble Alpes, UMR5168, F-38041 Grenoble, France CNRS, UMR5168, F-38054 Grenoble, France CEA, iRTSV, Laboratoire Physiologie Cellulaire et Végétale, F-38054 Grenoble, France INRA, F-38054 Grenoble, France.
authors.forename: Julia
authors.initials: J
authors.lastname: Engelhorn
authors.affiliation: Université Grenoble Alpes, UMR5168, F-38041 Grenoble, France CNRS, UMR5168, F-38054 Grenoble, France CEA, iRTSV, Laboratoire Physiologie Cellulaire et Végétale, F-38054 Grenoble, France INRA, F-38054 Grenoble, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Moreau
authors.affiliation: Plant Gene Expression Center, USDA-ARS/University of California, Berkeley, 800 Buchanan Street, Albany, CA 94710, USA.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Fletcher
authors.affiliation: Université Grenoble Alpes, UMR5168, F-38041 Grenoble, France CNRS, UMR5168, F-38054 Grenoble, France CEA, iRTSV, Laboratoire Physiologie Cellulaire et Végétale, F-38054 Grenoble, France INRA, F-38054 Grenoble, France Cristel.carles@ujf-grenoble.fr.
authors.forename: Cristel C
authors.initials: CC
authors.lastname: Carles
mesh_terms: D026342:AGAMOUS Protein, Arabidopsis / Q000235:genetics* / Q000378:metabolism; D000483:Alleles; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D035264:Flowers / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D008954:Models, Biological; D009154:Mutation; D063246:Organogenesis, Plant; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D026342:AGAMOUS Protein, Arabidopsis; D029681:Arabidopsis Proteins; D014157:Transcription Factors; C074747:LFY protein, Arabidopsis; C500130:At4g28190 protein, Arabidopsis
keywords: AGAMOUS; Arabidopsis thaliana; LEAFY; LFY; MADS domain-containing proteins; Organogenesis; ULT1; ULTRAPETALA1; activation of transcription; chromatin; flower determinacy; flower development; flower meristem identity; flower morphogenesis; trithorax group; trxG