title: Expression of the central growth regulator BIG BROTHER is regulated by multiple cis-elements.
abstract: BACKGROUND
  Much of the organismal variation we observe in nature is due to differences in organ size. The observation that even closely related species can show large, stably inherited differences in organ size indicates a strong genetic component to the control of organ size. Despite recent progress in identifying factors controlling organ growth in plants, our overall understanding of this process remains limited, partly because the individual factors have not yet been connected into larger regulatory pathways or networks. To begin addressing this aim, we have studied the upstream regulation of expression of BIG BROTHER (BB), a central growth-control gene in Arabidopsis thaliana that prevents overgrowth of organs. Final organ size and BB expression levels are tightly correlated, implying the need for precise control of its expression. BB expression mirrors proliferative activity, yet the gene functions to limit proliferation, suggesting that it acts in an incoherent feedforward loop downstream of growth activators to prevent over-proliferation.
  
  
  RESULTS
  To investigate the upstream regulation of BB we combined a promoter deletion analysis with a phylogenetic footprinting approach. We were able to narrow down important, highly conserved, cis-regulatory elements within the BB promoter. Promoter sequences of other Brassicaceae species were able to partially complement the A. thaliana bb-1 mutant, suggesting that at least within the Brassicaceae family the regulatory pathways are conserved.
  
  
  CONCLUSIONS
  This work underlines the complexity involved in precise quantitative control of gene expression and lays the foundation for identifying important upstream regulators that determine BB expression levels and thus final organ size.
authors.affiliation: Institut für Biochemie und Biologie, Universität Potsdam, Karl-Liebknecht Str. 24-25, D-14476 Potsdam, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Breuninger
authors.forename: Michael
authors.initials: M
authors.lastname: Lenhard
mesh_terms: D020121:5' Untranslated Regions; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D003001:Cloning, Molecular; D019295:Computational Biology; D017124:Conserved Sequence; D018744:DNA, Plant / Q000032:analysis / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D007210:Indoleacetic Acids / Q000378:metabolism; D010802:Phylogeny; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D050436:Regulatory Elements, Transcriptional; D016415:Sequence Alignment; D017384:Sequence Deletion; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D029681:Arabidopsis Proteins; D018744:DNA, Plant; D007210:Indoleacetic Acids; C515186:BIG BROTHER protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases