title: WOX5 suppresses CYCLIN D activity to establish quiescence at the center of the root stem cell niche.
abstract: In Arabidopsis, stem cells maintain the provision of new cells for root growth. They surround a group of slowly dividing cells named the quiescent center (QC), and, together, they form the stem cell niche (SCN). The QC acts as the signaling center of the SCN, repressing differentiation of the surrounding stem cells and providing a pool of cells able to replace damaged stem cells. Maintenance of the stem cells depends on the transcription factor WUSCHEL-RELATED HOMEOBOX 5 (WOX5), which is specifically expressed in the QC. However, the molecular mechanisms by which WOX5 promotes stem cell fate and whether WOX5 regulates proliferation of the QC are unknown. Here, we reveal a new role for WOX5 in restraining cell division in the cells of the QC, thereby establishing quiescence. In contrast, WOX5 and CYCD3;3/CYCD1;1 both promote cell proliferation in the nascent columella. The additional QC divisions occurring in wox5 mutants are suppressed in mutant combinations with the D type cyclins CYCD3;3 and CYCD1;1. Moreover, ectopic expression of CYCD3;3 in the QC is sufficient to induce cell division in the QC. WOX5 thus suppresses QC divisions that are otherwise promoted by CYCD3;3 and CYCD1;1, in part by interacting with the CYCD3;3 promoter to repress CYCD3;3 expression in the QC. Therefore, we propose a specific role for WOX5 in initiating and maintaining quiescence of the QC by excluding CYCD activity from the QC.
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, Wales, UK.
authors.forename: Celine
authors.initials: C
authors.lastname: Forzani
authors.affiliation: Faculty of Biology, BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Aichinger
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, Wales, UK.
authors.forename: Emily
authors.initials: E
authors.lastname: Sornay
authors.affiliation: Plant Developmental Biology, Wageningen University and Research Centre, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands.
authors.forename: Viola
authors.initials: V
authors.lastname: Willemsen
authors.affiliation: Faculty of Biology, BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Laux
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, Wales, UK. Electronic address: dewittew@cardiff.ac.uk.
authors.forename: Walter
authors.initials: W
authors.lastname: Dewitte
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, Wales, UK. Electronic address: murrayja1@cardiff.ac.uk.
authors.forename: James A H
authors.initials: JA
authors.lastname: Murray
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D002454:Cell Differentiation; D002455:Cell Division; D056743:Cyclin D3 / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development; D055153:Stem Cell Niche; D013234:Stem Cells / Q000166:cytology
chemical_list: D029681:Arabidopsis Proteins; C000596796:CYCD1;1 protein, Arabidopsis; C000596795:CYCD3;3 protein, Arabidopsis; D056743:Cyclin D3; D018398:Homeodomain Proteins; C116421:WUSCHEL protein, Arabidopsis