title: A bHLH-Based Feedback Loop Restricts Vascular Cell Proliferation in Plants.
abstract: Control of tissue dimensions in multicellular organisms requires the precise quantitative regulation of mitotic activity. In plants, where cells are immobile, tissue size is achieved through control of both cell division orientation and mitotic rate. The bHLH transcription factor heterodimer formed by target of monopteros5 (TMO5) and lonesome highway (LHW) is a central regulator of vascular width-increasing divisions. An important unanswered question is how its activity is limited to specify vascular tissue dimensions. Here we identify a regulatory network that restricts TMO5/LHW activity. We show that thermospermine synthase ACAULIS5 antagonizes TMO5/LHW activity by promoting the accumulation of SAC51-LIKE (SACL) bHLH transcription factors. SACL proteins heterodimerize with LHW-therefore likely competing with TMO5/LHW interactions-prevent activation of TMO5/LHW target genes, and suppress the over-proliferation caused by excess TMO5/LHW activity. These findings connect two thus-far disparate pathways and provide a mechanistic understanding of the quantitative control of vascular tissue growth.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Vera-Sirera
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 Wageningen, the Netherlands.
authors.forename: Bert
authors.initials: B
authors.lastname: De Rybel
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Úrbez
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 Wageningen, the Netherlands.
authors.forename: Evangelos
authors.initials: E
authors.lastname: Kouklas
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Pesquera
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Juan Camilo
authors.initials: JC
authors.lastname: Álvarez-Mahecha
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Eugenio G
authors.initials: EG
authors.lastname: Minguet
authors.affiliation: Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, 90187 Umeå, Sweden.
authors.forename: Hannele
authors.initials: H
authors.lastname: Tuominen
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Carbonell
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 Wageningen, the Netherlands; Microspectroscopy Center, Wageningen University, Dreijenlaan 3, 6703 Wageningen, the Netherlands.
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Borst
authors.affiliation: Laboratory of Biochemistry, Wageningen University, Dreijenlaan 3, 6703 Wageningen, the Netherlands. Electronic address: dolf.weijers@wur.nl.
authors.forename: Dolf
authors.initials: D
authors.lastname: Weijers
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain. Electronic address: mblazquez@ibmcp.upv.es.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Blázquez
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018517:Plant Roots / Q000166:cytology* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D052584:Xylem / Q000166:cytology* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D012333:RNA, Messenger; D015534:Trans-Activators; C414439:ACAULIS5 protein, Arabidopsis; C523529:LHW protein, Arabidopsis; C515850:SAC51 protein, Arabidopsis; C549371:TARGET OF MP 5 protein, Arabidopsis