title: ASYMMETRIC LEAVES1 regulates abscission zone placement in Arabidopsis flowers.
abstract: BACKGROUND
  The sepals, petals and stamens of Arabidopsis flowers detach via abscission zones formed at their boundaries with the underlying receptacle. The ASYMMETRIC LEAVES1 (AS1) MYB transcription factor plays a critical role in setting boundaries between newly formed leaf primordia and the shoot meristem. By repressing expression of a set of KNOTTED1-LIKE HOMEODOMAIN (KNOX) genes from developing leaf primordia, AS1 and its partner ASYMMETRIC LEAVES2 allow the patterning and differentiation of leaves to proceed. Here we show a unique role for AS1 in establishing the positions of the sepal and petal abscission zones in Arabidopsis flowers.
  
  
  RESULTS
  In as1 mutant flowers, the sepal abscission zones are displaced into inverted V-shaped positions, leaving behind triangular stubs of tissue when the organs abscise. Movement of the petal abscission zones is also apparent. Abscission of the medial sepals is delayed in as1 flowers; loss of chlorophyll in the senescing sepals contrasts with proximal zones that remain green. AS1 has previously been shown to restrict expression of the KNOX gene, BREVIPEDICELLUS (BP), from the sepals. We show here that loss of BP activity in as1 flowers is sufficient to restore the positions of the sepal and petal abscission zones, the sepal-receptacle boundary of the medial sepals and the timing of their abscission.
  
  
  CONCLUSIONS
  Our results indicate that AS1 activity is critical for the proper placement of the floral organ abscission zones, and influences the timing of organ shedding.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Gubert
authors.forename: Megan E
authors.initials: ME
authors.lastname: Christy
authors.forename: Denise L
authors.initials: DL
authors.lastname: Ward
authors.forename: William D
authors.initials: WD
authors.lastname: Groner
authors.affiliation: Department of Biology, University of Mississippi, Oxford 38677, MS, USA. liljegren@olemiss.edu.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Liljegren
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism / Q000502:physiology*; D018389:Codon, Nonsense; D035264:Flowers / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism; D017434:Protein Structure, Tertiary; D014157:Transcription Factors / Q000502:physiology*
chemical_list: C456239:ASYMMETRIC LEAVES1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D018389:Codon, Nonsense; D018398:Homeodomain Proteins; C092212:KNAT1 protein, Arabidopsis; D014157:Transcription Factors