title: Carpeloidy in flower evolution and diversification: a comparative study in Carica papaya and Arabidopsis thaliana.
abstract: OBJECTIVE
  Bisexual flowers of Carica papaya range from highly regular flowers to morphs with various fusions of stamens to the ovary. Arabidopsis thaliana sup1 mutants have carpels replaced by chimeric carpel-stamen structures. Comparative analysis of stamen to carpel conversions in the two different plant systems was used to understand the stage and origin of carpeloidy when derived from stamen tissues, and consequently to understand how carpeloidy contributes to innovations in flower evolution.
  
  
  METHODS
  Floral development of bisexual flowers of Carica was studied by scanning electron microscopy and was compared with teratological sup mutants of A. thaliana.
  
  
  RESULTS
  In Carica development of bisexual flowers was similar to wild (unisexual) forms up to locule initiation. Feminization ranges from fusion of stamen tissue to the gynoecium to complete carpeloidy of antepetalous stamens. In A. thaliana, partial stamen feminization occurs exclusively at the flower apex, with normal stamens forming at the periphery. Such transformations take place relatively late in development, indicating strong developmental plasticity of most stamen tissues. These results are compared with evo-devo theories on flower bisexuality, as derived from unisexual ancestors. The Arabidopsis data highlight possible early evolutionary events in the acquisition of bisexuality by a patchy transformation of stamen parts into female parts linked to a flower axis-position effect. The Carica results highlight tissue-fusion mechanisms in angiosperms leading to carpeloidy once bisexual flowers have evolved.
  
  
  CONCLUSIONS
  We show two different developmental routes leading to stamen to carpel conversions by late re-specification. The process may be a fundamental aspect of flower development that is hidden in most instances by developmental homeostasis.
authors.affiliation: Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK. l.ronsedecraene@rbge.ac.uk
authors.forename: Louis
authors.initials: L
authors.lastname: Ronse De Craene
authors.forename: Christophe
authors.initials: C
authors.lastname: Tréhin
authors.forename: Patrice
authors.initials: P
authors.lastname: Morel
authors.forename: Ioan
authors.initials: I
authors.lastname: Negrutiu
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics*; D005075:Biological Evolution; D029441:Carica / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D035264:Flowers / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D018519:Meristem / Q000254:growth & development; D008855:Microscopy, Electron, Scanning; D009154:Mutation; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D014157:Transcription Factors; C096661:superman protein, Arabidopsis