Imaging plant growth in 4D: robust tissue reconstruction and lineaging at cell resolution

The stereotypic pattern of cell shapes in the Arabidopsis shoot apical meristem (SAM) suggests that strict rules govern the placement of new walls during cell division. When a cell in the SAM divides, a new wall is built that connects existing walls and divides the cytoplasm of the daughter cells. Because features that are determined by the placement of new walls such as cell size, shape, and number of neighbors are highly regular, rules must exist for maintaining such order. Here we present a quantitative model of these rules that incorporates different observed features of cell division. Each feature is incorporated into a "potential function" that contributes a single term to a total analog of potential energy. New cell walls are predicted to occur at locations where the potential function is minimized. Quantitative terms that represent the well-known historical rules of plant cell division, such as those given by Hofmeister, Errera, and Sachs are developed and evaluated against observed cell divisions in the epidermal layer (L1) of Arabidopsis thaliana SAM. The method is general enough to allow additional terms for nongeometric properties such as internal concentration gradients and mechanical tensile forces.cell division | computer modeling | live imaging | Arabidopsis T he Arabidopsis shoot apical meristem (SAM) is a structure at the tip of the shoot that is responsible for generating almost all of the above-ground tissue of the plant (1). Its epidermal and subepidermal cells are organized into layers with very few cells moving between layers (2, 3). When these cells expand they do so laterally, pushing other cells toward the periphery of the meristem. Division in these cells is anticlinal such that each layer remains one cell thick. The underlying mechanism determining the location of new cell walls is unknown but the qualitative properties of meristematic cell division are well documented (4-8). Perhaps the best known summary is Errera's rule, derived following observations of soap bubble formation. In the modern interpretation, the plane of division corresponds to the shortest path that will halve the mother cell. Errera, in fact, wrote that the wall would be a surface "mit constanter mittlerer Krümmung (= Minimalfläche) [with constant mean curvature (= minimal area)]" (4). Because this does not specify a location for the new cell wall, more recent authors have added to this that the mother cell divides evenly (9, 10). With this modification, Errera's rule is easily quantifiable.A second observation is Hofmeister's rule: New cell walls usually form in a plane normal to the principal axis of cell elongation (5). This rule is more difficult to quantify, because the principal axis of cell elongation is often confused with the direction of growth. Cells are asymmetrical and hence a principal direction of cell elongation can easily be calculated (e.g., the principal axis of inertia or principal component of a segmentation). The assumption is often made that because the cell is more elongated in one direction...

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Analysis of cell division patterns in the Arabidopsis shoot apical meristem

Shapiro

Tobin

Mjolsness

et al. 2015

“…To reconstruct a 3D surface view of the LRP shape, we used image analysis software (8) to integrate confocal z-stacks of LRP at selected stages (Movies S2 and S3). These data were used for an in-depth investigation of LRP morphogenesis in 3D up to the acquisition of meristematic identity.…”

Section: Three-and Four-dimensional Image Analysis Reveals That Lrpsmentioning

confidence: 99%

“…Recent advances in live biological imaging and image analysis (8,9) now make it possible to address how Arabidopsis LRPs are built in three and four dimensions. Here, we report how 3D/4D image reconstruction reveals important divisions that are responsible for the transition from a bilateral to a radial symmetry of the LRP.…”

mentioning

confidence: 99%

Lateral root morphogenesis is dependent on the mechanical properties of the overlaying tissues

Lucas

Kenobi

Wangenheim

et al. 2013

Self Cite

216

186

In Arabidopsis, lateral root primordia (LRPs) originate from pericycle cells located deep within the parental root and have to emerge through endodermal, cortical, and epidermal tissues. These overlaying tissues place biomechanical constraints on the LRPs that are likely to impact their morphogenesis. This study probes the interplay between the patterns of cell division, organ shape, and overlaying tissues on LRP morphogenesis by exploiting recent advances in live plant cell imaging and image analysis. Our 3D/4D image analysis revealed that early stage LRPs exhibit tangential divisions that create a ring of cells corralling a population of rapidly dividing cells at its center. The patterns of division in the latter population of cells during LRP morphogenesis are not stereotypical. In contrast, statistical analysis demonstrated that the shape of new LRPs is highly conserved. We tested the relative importance of cell division pattern versus overlaying tissues on LRP morphogenesis using mutant and transgenic approaches. The double mutant aurora1 (aur1) aur2 disrupts the pattern of LRP cell divisions and impacts its growth dynamics, yet the new organ's dome shape remains normal. In contrast, manipulating the properties of overlaying tissues disrupted LRP morphogenesis. We conclude that the interaction with overlaying tissues, rather than the precise pattern of divisions, is most important for LRP morphogenesis and optimizes the process of lateral root emergence.lateral root development | plant morphogenesis | biomechanical regulation | statistical shape analysis | Arabidopsis thaliana I n contrast to animals, only the basic blueprint of the plant body plan is laid out during embryogenesis. Instead, the majority of plant organs are formed postembryonically. In some instances, organ formation can occur deep within another organ, as is the case for lateral roots (1, 2). In addition, plant cells are constrained by rigid walls; hence, cell migration cannot occur. Instead, plant morphogenesis relies on two mechanisms: oriented cell division and anisotropic growth (3, 4). For example, during embryogenesis, cells exhibit a highly synchronized program of expansion and division (5). How cell division, cell shape, and overlaying tissues interact during plant organ morphogenesis is currently unclear.Lateral roots are derived from cell division events deep within the primary root (1, 2). Pairs of pericycle cells in several adjacent files undergo a series of asymmetric formative divisions (reviewed in ref. 6). These periclinal (parallel) and anticlinal (perpendicular) divisions give birth to a lateral root primordium (LRP) that will develop further into a lateral root comprising a new root meristem. LRP formation in Arabidopsis was first described in a pioneering study 14 years ago (7) that proposed a seven-stage taxonomy of LRP development on the basis of 2D observations of cell layer numbers that still forms the basis of all studies describing LRP development in Arabidopsis.Recent advances in live biological imaging and image ...

“…Deep-tissue live-imaging techniques provide the means for visualizing outlines of entire cells with a temporal resolution of a few seconds (8). However, most previously proposed methods for studying cell shape changes are restricted to 2D cross-sections of cells (22), whereas those methods enabling whole-cell reconstructions are limited to relatively simple and static shapes (23,24) or rely heavily on manual editing (25). Here, we therefore developed a cell shape analysis tool, called Embryo Development Geometry Explorer (EDGE), which is optimized for analyzing the fast dynamics of whole-cell shape changes in three spatial dimensions plus time in planar sheets of cells.…”

mentioning

confidence: 99%

Volume conservation principle involved in cell lengthening and nucleus movement during tissue morphogenesis

Gelbart

Martin

et al. 2012

131

124

Tissue morphogenesis is the process in which coordinated movements and shape changes of large numbers of cells form tissues, organs, and the internal body structure. Understanding morphogenetic movements requires precise measurements of whole-cell shape changes over time. Tissue folding and invagination are thought to be facilitated by apical constriction, but the mechanism by which changes near the apical cell surface affect changes along the entire apical-basal axis of the cell remains elusive. Here, we developed Embryo Development Geometry Explorer, an approach for quantifying rapid whole-cell shape changes over time, and we combined it with deep-tissue time-lapse imaging based on fast two-photon microscopy to study Drosophila ventral furrow formation. We found that both the cell lengthening along the apical-basal axis and the movement of the nucleus to the basal side proceeded stepwise and were correlated with apical constriction. Moreover, cell volume lost apically due to constriction largely balanced the volume gained basally by cell lengthening. The volume above the nucleus was conserved during its basal movement. Both apical volume loss and cell lengthening were absent in mutants showing deficits in the contractile cytoskeleton underlying apical constriction. We conclude that a single mechanical mechanism involving volume conservation and apical constriction-induced basal movement of cytoplasm accounts quantitatively for the cell shape changes and the nucleus movement in Drosophila ventral furrow formation. Our study provides a comprehensive quantitative analysis of the fast dynamics of whole-cell shape changes during tissue folding and points to a simplified model for Drosophila gastrulation.two-photon imaging | 4D reconstruction | segmentation