title: Cell size and growth regulation in the Arabidopsis thaliana apical stem cell niche.
abstract: Cell size and growth kinetics are fundamental cellular properties with important physiological implications. Classical studies on yeast, and recently on bacteria, have identified rules for cell size regulation in single cells, but in the more complex environment of multicellular tissues, data have been lacking. In this study, to characterize cell size and growth regulation in a multicellular context, we developed a 4D imaging pipeline and applied it to track and quantify epidermal cells over 3-4 d in Arabidopsis thaliana shoot apical meristems. We found that a cell size checkpoint is not the trigger for G2/M or cytokinesis, refuting the unexamined assumption that meristematic cells trigger cell cycle phases upon reaching a critical size. Our data also rule out models in which cells undergo G2/M at a fixed time after birth, or by adding a critical size increment between G2/M transitions. Rather, cell size regulation was intermediate between the critical size and critical increment paradigms, meaning that cell size fluctuations decay by ∼75% in one generation compared with 100% (critical size) and 50% (critical increment). Notably, this behavior was independent of local cell-cell contact topologies and of position within the tissue. Cells grew exponentially throughout the first >80% of the cell cycle, but following an asymmetrical division, the small daughter grew at a faster exponential rate than the large daughter, an observation that potentially challenges present models of growth regulation. These growth and division behaviors place strong constraints on quantitative mechanistic descriptions of the cell cycle and growth control.
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.|Department of Bioengineering, Stanford University, Stanford, CA 94305.
authors.forename: Lisa
authors.initials: L
authors.lastname: Willis
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.
authors.forename: Yassin
authors.initials: Y
authors.lastname: Refahi
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.
authors.forename: Raymond
authors.initials: R
authors.lastname: Wightman
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.
authors.forename: Benoit
authors.initials: B
authors.lastname: Landrein
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.
authors.forename: José
authors.initials: J
authors.lastname: Teles
authors.affiliation: Department of Bioengineering, Stanford University, Stanford, CA 94305.|Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305.
authors.forename: Kerwyn Casey
authors.initials: KC
authors.lastname: Huang
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom.|Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125.|Division of Biology and Biological Engineering 156-29, California Institute of Technology, Pasadena, CA 91125.
authors.forename: Elliot M
authors.initials: EM
authors.lastname: Meyerowitz
authors.affiliation: The Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, United Kingdom; henrik.jonsson@slcu.cam.ac.uk.|Computational Biology and Biological Physics, Lund University, 223 62 Lund, Sweden.|Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Cambridge CB3 0DZ, United Kingdom.
authors.forename: Henrik
authors.identifier: 0000-0003-2340-588X
authors.initials: H
authors.lastname: Jönsson
mesh_terms: D017360:Arabidopsis / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D002453:Cell Cycle; D002455:Cell Division; D002462:Cell Membrane / Q000378:metabolism; D048429:Cell Size; D004261:DNA Replication; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006706:Homeostasis; D008164:Luminescent Proteins / Q000378:metabolism; D018519:Meristem / Q000254:growth & development*; D016011:Normal Distribution; D018520:Plant Shoots / Q000254:growth & development; D055153:Stem Cell Niche
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D008164:Luminescent Proteins; C054562:yellow fluorescent protein, Bacteria
keywords: cell cycle; cell growth; cell size; homeostasis; plant stem cells