Biology subjects

Braybrook, S. A.

Publications and source records attributed to Braybrook, S. A..

8 recordsLinked to original sources

bioRxiv2023

The maize preligule band is subdivided into distinct domains with contrasting cellular properties prior to ligule outgrowth

The maize ligule is a fringe of epidermis-derived tissue, which arises from the preligule band (PLB) at a boundary between the blade and sheath. A hinge-like auricle also develops immediately distal to the ligule and contributes to blade angle. Here, we characterize the stages of PLB and early ligule development in terms of topography, cell area, division orientation, cell wall rigidity, and auxin response dynamics. Differential thickening of epidermal cells and localized periclinal divisions contributed to the formation of a ridge within the PLB, which ultimately produces the ligule fringe. Patterns in cell wall rigidity were consistent with the subdivision of the PLB into two regions along a distinct line positioned at the nascent ridge. The proximal region produces the ligule, while the distal region contributes to one epidermal face of the auricles. Whereas the auxin transporter PIN1 accumulated in the PLB, observed differential auxin transcriptional response did not underlie the partitioning of the PLB. Our data demonstrate that two zones with contrasting cellular properties, the preligule and preauricle, are specified within the ligular region prior to ligule outgrowth. Summary StatementChanges in cell geometry, division orientation, and cell wall mechanics underlie maize ligule morphogenesis. The establishment of mechanically distinct epidermal domains coincides with topographical changes during early ligule outgrowth.

plant biology↗

bioRxiv2020

Identification and selection of optimal reference genes for qPCR-based gene expression analysis in Fucus distichus under various abiotic stresses

Quantitative gene expression analysis is an important tool in the scientists belt. The identification of evenly expressed reference genes is necessary for accurate quantitative gene expression analysis, whether by traditional RT-PCR (reverse-transcription polymerase chain reaction) or by qRT-PCR (quantitative real-time PCR; qPCR). In the Stramenopiles (the major line of eukaryotes that includes brown algae) there is a noted lack of known reference genes for such studies, largely due to the absence of available molecular tools. Here we present a set of nine reference genes (Elongation Factor 1 alpha (EF1A), Elongation Factor 2 alpha (EF2A), Elongation Factor 1 beta (EF1B), 14-3-3 Protein, Ubiquitin Conjugating Enzyme (UBCE2), Glyceraldehyde-3-phosphate Dehydrogenase (GAPDH), Actin Related Protein Complex (ARP2/3), Ribosomal Protein (40s; S23), and Actin) for the brown alga Fucus distichus. These reference genes were tested on adult sporophytes across six abiotic stress conditions (desiccation, light and temperature modification, hormone addition, pollutant exposure, nutrient addition, and wounding). Suitability of these genes as reference genes was quantitatively evaluated across conditions using standard methods and the majority of the tested genes were evaluated favorably. However, we show that normalization genes should be chosen on a condition-by-condition basis. We provide a recommendation that at least two reference genes be used per experiment, a list of recommended pairs for the conditions tested here, and a procedure for identifying a suitable set for an experimenters unique design. With the recent expansion of interest in brown algal biology and accompanied molecular tools development, the variety of experimental conditions tested here makes this study a valuable resource for future work in basic biology and understanding stress responses in the brown algal lineage.

molecular biology↗

bioRxiv2020

Growth of the Fucus embryo: insights into wall-mediated cell expansion through mechanics and transcriptomics

Morphogenesis in walled organisms represents a highly controlled process that involves cell proliferation and expansion; cell growth is regulated through changes in the structure and mechanics of the cells walls. Despite taking different evolutionary paths, land plants and some brown algae exhibit developmental and morphological similarities; however, the role of the algal cell wall in morphogenesis remains heavily underexplored. Cell expansion in plants is hypothesized to involve modifications of hemicellulose linkages and pectin gelation in the cell wall. Little is known about the wall-based control of cell expansion in brown algae; however, the algal analog to pectin, alginate, exhibits different gelation depending on its biochemistry. Here we show that cell wall mechanics and alginate biochemistry are correlated with cell expansion versus proliferation in the developing Fucus serratus embryo. In the elongating cells of the embryo rhizoid, we found a reduced cell wall stiffness and lower amounts of stiffer alginate epitopes. In comparison, the early embryo thallus was shown to undergo cleavage-type cell proliferation, without expansion, and this was correlated with higher amounts of stiff alginate epitopes and increased wall stiffness. An embryo development RNAseq dataset was generated to characterize differential gene expression during development. This data set allowed for identification of many enriched GO functions through developmental time. In addition, the transcriptome allowed for the identification of cell-wall related genes whose differential expression may underlie our observed growth phenotypes. We propose that differential gene expression of genes involved in alginate stiffness are strong candidates underlying differential wall stiffness and cell elongation in the developing Fucus embryo. Our results show that wall-driven cellular expansion mechanisms in brown algae are similar to those observed in plants. In addition, our data show that cleavage-type cell proliferation exists in brown algae similar to that seen in plant and animal systems indicating a possible conserved developmental phenomenon across the branches of multicellular life.

developmental biology↗

bioRxiv2019

On Pectin Methyl-esterification: Implications for In vitro and In vivo Viscoelasticity

Pectin is a major component of the primary plant cell wall and is important for cell expansion. However, the relationship between its chemistry and mechanical properties is not fully understood, especially in vivo. In this study, a protocol for viscoelastic micro-indentation using atomic force microscopy (AFM) was developed and applied to pectin in vitro and in vivo. After determining that linear viscoelasticity was a suitable theoretical framework for in vitro pectin analyses were conducted with both a standard linear solid and fractional Zener model. These indicated a strong coupling between elastic and viscous properties over a range of degrees of methyl-esterification (DM). Both elasticity and viscosity were found to vary non-linearly with DM which had interesting consequences for pectin gels of mixed DM. In Arabidopsis cell walls, the standard linear solid model was found to be appropriate. In this in vivo composite material a weaker elastic-viscous coupling was exhibited, correlated with DM. The viscoelastic testing in vivo of rapidly elongating cell walls, rich in high DM pectin, displayed a longer viscous time-scale. The implications of the testing method and results are discussed in the context of mechanobiology, mechano-chemistry, and cell growth.

plant biology↗

bioRxiv2018

Of puzzles and pavements: a quantitative exploration of leaf epidermal cell shape

SummaryThe epidermal cells of leaves lend themselves readily to observation and display many shapes and types: tabular pavement cells, complex trichomes, and stomatal complexes1. Pavement cells from Zea mays (maize) and Arabidopsis thaliana (arabidopsis) both have highly undulate anticlinal walls and are held as representative of monocots and eudicots, respectively. In these two model species, we have a nuanced understanding of the molecular mechanisms that generate undulating pavement cell shape2-9. This model-system dominance has led to two common assumptions: first, that particular plant lineages are characterized by particular pavement cell shapes; and second, that undulatory pavement cell shapes are common enough to be model shapes. To test these assumptions, we quantified pavement cell shape in the leaves of 278 vascular plant taxa and assessed cell shape metrics across large taxonomic groups. We settled on two metrics that described cell shape diversity well in this dataset: aspect ratio (degree of cell elongation) and solidity (a proxy for margin undulation). We found that pavement cells in the monocots tended to have weakly undulating margins, pavement cells in ferns had strongly undulating margins, and pavement cells in the eudicots showed no particular degree of undulation. Indeed, we found that cells with strongly undulating margins, like those of arabidopsis and maize, were in the minority in seed plants. At the organ level, we found a trend towards cells with more undulating margins on the abaxial leaf surface vs. the adaxial surface. We also detected a correlation between cell and leaf aspect ratio: highly elongated leaves tended to have highly elongated cells (low aspect ratio), but not in the eudicots. This indicates that while plant anatomy and plant morphology can be connected, superficially similar leaves can develop through very different underlying growth dynamics (cell expansion and division patterns). This work reveals the striking diversity of pavement cell shapes across vascular plants, and lays the quantitative groundwork for testing hypotheses about pavement cell form and function.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=139 SRC=\"FIGDIR/small/361717_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (83K):\norg.highwire.dtl.DTLVardef@1a571a8org.highwire.dtl.DTLVardef@c8cf7dorg.highwire.dtl.DTLVardef@1ae3090org.highwire.dtl.DTLVardef@f666ce_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2018

Anisotropic growth is achieved through the additive mechanical effect of material anisotropy and elastic asymmetry

Fast directional growth is a necessity for the young seedling: after germination, the seedling needs to quickly reach through the soil to begin its autotrophic life. In most dicot plants, this rapid escape is due to the anisotropic elongation of the hypocotyl, the columnar organ between the root and the shoot meristems. Such anisotropic growth is common in many plant organs and is canonically attributed to cell wall anisotropy produced by oriented cellulose fibers in the cell wall. More recently, a mechanism based on asymmetric cell wall elasticity has been proposed, produced by differential pectin biochemistry. Here we present a harmonizing model for anisotropic growth control in the dark-grown Arabidopsis hypocotyl: basic anisotropic information is provided by cellulose orientation (proxied by microtubules) and additive anisotropic information is provided by pectin-based elastic asymmetry in the epidermis. We demonstrate that hypocotyl growth was always anisotropic with axial and transverse walls growing differently, from germination. We present experimental evidence for pectin biochemical differences and wall mechanics underlying this differential growth. We demonstrate that pectin biochemical changes control the transition to rapid growth characteristic of Arabidopsis hypocotyl elongation, and provide evidence for a substantial mechanical role for pectin in the cell wall when microtubules are compromised. Lastly, our in silico modelling experiments indicate an additive combination for pectin biochemistry and cellulose orientation in promoting anisotropic growth.

plant biology↗

bioRxiv2017

An automated confocal micro-extensometer enables in vivo quantification of mechanical properties with cellular resolution.

How complex developmental-genetic networks are translated into organs with specific 3D shapes remains an open question. This question is particularly challenging because the elaboration of specific shapes is in essence a question of mechanics. In plants, this means how the genetic circuitry affects the cell wall. The mechanical properties of the wall and their spatial variation are the key factors controlling morphogenesis in plants. However, these properties are difficult to measure and investigating their relation to genetic regulation is particularly challenging. To measure spatial variation of mechanical properties, one must determine the deformation of a tissue in response to a known force with cellular resolution. Here we present an automated confocal micro-extensometer (ACME), which greatly expands the scope of existing methods for measuring mechanical properties. Unlike classical extensometers, ACME is mounted on a confocal microscope and utilizes confocal images to compute the deformation of the tissue directly from biological markers, thus providing cellular scale information and improved accuracy. ACME is suitable for measuring the mechanical responses in live tissue. As a proof of concept we demonstrate that the plant hormone gibberellic acid induces a spatial gradient in mechanical properties along the length of the Arabidopsis hypocotyl.\n\nTerms

plant biology↗

bioRxiv2017

Towards An Understanding Of Spiral Patterning In The Sargassum muticum Shoot Apex

In plants and parenchymatous brown algae the body arises through the activity of an apical meristem (a niche of cells or a single cell). The meristem produces lateral organs in specific patterns, referred to as phyllotaxis. In plants, two different control mechanisms have been proposed - one is position-dependent and relies on morphogen accumulation at future organ sites whereas the other is a lineage-based system which links phyllotaxis to the apical cell division pattern. Here we examine the apical patterning of the brown alga, Sargassum muticum, which exhibits spiral phyllotaxis (137.5{degrees} angle) and an unlinked apical cell division pattern. The Sargassum apex presents characteristics of a self-organising system, similar to plant meristems. We were unable to correlate the plant morphogen auxin with bud positioning in Sargassum, nor could we predict cell wall softening at new bud sites. Our data suggests that in Sargassum muticum there is no connection between phyllotaxis and the apical cell division pattern indicating a position-dependent patterning mechanism may be in place. The underlying mechanisms behind the phyllotactic patterning appear to be distinct from those seen in plants.\n\nSummaryThe brown alga Sargassum muticum displays spiral phyllotaxis developed from a position-dependent self-organising mechanism, different from that understood in plants.

developmental biology↗