title: SEPALLATA3: the 'glue' for MADS box transcription factor complex formation.
abstract: BACKGROUND
  Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study.
  
  
  RESULTS
  In total, 106 multimeric complexes were identified; in more than half of these at least one SEP protein was present. Besides the known complexes involved in determining floral organ identity, various complexes consisting of combinations of proteins known to play a role in floral organ identity specification, and flowering time determination were discovered. The capacity to form this latter type of complex suggests that homeotic factors play essential roles in down-regulation of the MADS box genes involved in floral timing in the flower via negative auto-regulatory loops. Furthermore, various novel complexes were identified that may be important for the direct regulation of the floral transition process. A subsequent detailed analysis of the APETALA3, PISTILLATA, and SEP3 proteins in living plant cells suggests the formation of a multimeric complex in vivo.
  
  
  CONCLUSIONS
  Overall, these results provide strong indications that higher-order complex formation is a general and essential molecular mechanism for plant MADS box protein functioning and attribute a pivotal role to the SEP3 'glue' protein in mediating multimerization.
authors.affiliation: Plant Research International, Bioscience, Droevendaalsesteeg 1, Wageningen, the Netherlands. richard.immink@wur.nl
authors.forename: Richard G H
authors.initials: RG
authors.lastname: Immink
authors.forename: Isabella A N
authors.initials: IA
authors.lastname: Tonaco
authors.forename: Stefan
authors.initials: S
authors.lastname: de Folter
authors.forename: Anna
authors.initials: A
authors.lastname: Shchennikova
authors.forename: Aalt D J
authors.initials: AD
authors.lastname: van Dijk
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Busscher-Lange
authors.forename: Jan W
authors.initials: JW
authors.lastname: Borst
authors.forename: Gerco C
authors.initials: GC
authors.lastname: Angenent
mesh_terms: D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000502:physiology*; D035264:Flowers / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018398:Homeodomain Proteins / Q000502:physiology*; D026161:MADS Domain Proteins / Q000378:metabolism*; D046912:Multiprotein Complexes; D055503:Protein Multimerization; D014157:Transcription Factors / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D018398:Homeodomain Proteins; D026161:MADS Domain Proteins; D046912:Multiprotein Complexes; C121158:SEP3 protein, Arabidopsis; D014157:Transcription Factors