121 research outputs found
Modelling meristem development in plants
Get PDFMeristems continually supply new cells for post-embryonic plant development and coordinate the initiation of new organs, such as leaves and flowers. Meristem function is regulated by a large and interconnected dynamic system that includes transcription networks, intercellular protein signalling, polarized transport of hormones and a constantly changing cellular topology. Mathematical modelling, in which the dynamics of a system are simulated using explicitly defined interactions, can serve as a powerful tool for examining the expected behaviour of such a system given our present knowledge and assumptions. Modelling can also help to investigate new hypotheses in silico both to validate ideas and to obtain inspiration for new experiments. Several recent studies have used new molecular data together with modelling and computational techniques to investigate meristem function
Auxin is not asymmetrically distributed in initiating Arabidopsis leaves
No full textAbstractIt has been proposed that asymmetric auxin levels within initiating leaves help establish leaf polarity, based in part on observations of the DII auxin sensor. Here we show that the mDII control sensor also exhibits an asymmetry and that according to the ratio-metric auxin sensor R2D2, no obvious asymmetry in auxin exists. Together with other recent findings, our results argue against the importance of auxin asymmetry in establishing leaf polarity.</jats:p
Self-organizing periodicity in development: organ positioning in plants
No full textABSTRACTPeriodic patterns during development often occur spontaneously through a process of self-organization. While reaction-diffusion mechanisms are often invoked, other types of mechanisms that involve cell-cell interactions and mechanical buckling have also been identified. Phyllotaxis, or the positioning of plant organs, has emerged as an excellent model system to study the self-organization of periodic patterns. At the macro scale, the regular spacing of organs on the growing plant shoot gives rise to the typical spiral and whorled arrangements of plant organs found in nature. In turn, this spacing relies on complex patterns of cell polarity that involve feedback between a signaling molecule – the plant hormone auxin – and its polar, cell-to-cell transport. Here, we review recent progress in understanding phyllotaxis and plant cell polarity and highlight the development of new tools that can help address the remaining gaps in our understanding.</jats:p
Antagonistic Regulation of PIN Phosphorylation by PP2A and PINOID Directs Auxin Flux
Get PDFSummaryIn plants, cell polarity and tissue patterning are connected by intercellular flow of the phytohormone auxin, whose directional signaling depends on polar subcellular localization of PIN auxin transport proteins. The mechanism of polar targeting of PINs or other cargos in plants is largely unidentified, with the PINOID kinase being the only known molecular component. Here, we identify PP2A phosphatase as an important regulator of PIN apical-basal targeting and auxin distribution. Genetic analysis, localization, and phosphorylation studies demonstrate that PP2A and PINOID both partially colocalize with PINs and act antagonistically on the phosphorylation state of their central hydrophilic loop, hence mediating PIN apical-basal polar targeting. Thus, in plants, polar sorting by the reversible phosphorylation of cargos allows for their conditional delivery to specific intracellular destinations. In the case of PIN proteins, this mechanism enables switches in the direction of intercellular auxin fluxes, which mediate differential growth, tissue patterning, and organogenesis
Auxin Acts through MONOPTEROS to Regulate Plant Cell Polarity and Pattern Phyllotaxis.
Get PDFThe periodic formation of plant organs such as leaves and flowers gives rise to intricate patterns that have fascinated biologists and mathematicians alike for hundreds of years [1]. The plant hormone auxin plays a central role in establishing these patterns by promoting organ formation at sites where it accumulates due to its polar, cell-to-cell transport [2-6]. Although experimental evidence as well as modeling suggest that feedback from auxin to its transport direction may help specify phyllotactic patterns [7-12], the nature of this feedback remains unclear [13]. Here we reveal that polarization of the auxin efflux carrier PIN-FORMED 1 (PIN1) is regulated by the auxin response transcription factor MONOPTEROS (MP) [14]. We find that in the shoot, cell polarity patterns follow MP expression, which in turn follows auxin distribution patterns. By perturbing MP activity both globally and locally, we show that localized MP activity is necessary for the generation of polarity convergence patterns and that localized MP expression is sufficient to instruct PIN1 polarity directions non-cell autonomously, toward MP-expressing cells. By expressing MP in the epidermis of mp mutants, we further show that although MP activity in a single-cell layer is sufficient to promote polarity convergence patterns, MP in sub-epidermal tissues helps anchor these polarity patterns to the underlying cells. Overall, our findings reveal a patterning module in plants that determines organ position by orienting transport of the hormone auxin toward cells with high levels of MP-mediated auxin signaling. We propose that this feedback process acts broadly to generate periodic plant architectures
Context-specific functions of transcription factors controlling plant development : From leaves to flowers
No full textPlant development is regulated by transcription factors that often act in more than one process and stage of development. Yet the molecular mechanisms that govern the functional diversity and specificity of these proteins remains far from understood. Flower development provides an ideal context to study these mechanisms since the development of distinct floral organs depends on similar but distinct combinations of transcriptional regulators. Recent work also highlights the importance of leaf polarity regulators as additional key factors in flower initiation, floral organ morphogenesis, and possibly floral organ positioning. A detailed understanding of how these factors work in combination will enable us to address outstanding questions in flower development including how distinct shapes and positions of floral organs are generated. Experimental approaches and computer-based modeling will be required to characterize gene-regulatory networks at the level of single cells
Hay - Charles A. Hay
No full textA.B.; D.D., 1859; salutatorian; Philomathaean, orator, anniversary, 1839; Linnaean; entered sophomore class, 1836. Prepared at schools in York and under Dr. Morris. Grad. Gettysburg Seminary, 1841; student, Berlin and Halle, German, 1841-43. Born Feb. 11, 1821, York. Parents, John and Eliza. Lutheran clergyman: Middletown, 1844; Hanover, 1848-49; Harrisburg, 1849-65; Christ, Gettysburg, 1866-93. Prof. of Biblical Literature and German, Gettysburg Seminary, 1844-48; prof. of German, Gettysburg College, 1844-48; prof. of Hebrew, Old Testament Theology and German, Gettysburg Sem., 1865-93. Pres., General Syn., 1881; trustee, Gettysburg College, 1852-93; sec. of board, same, 1867-80. author, Life Sketches of Lutheran Ministers in America. Translator: Luther's Commentary on the Sermon on the Mount; Schmid's Dogmatic Theology. Died June 26, 1893. Married May 5, 1845, Sarah Rebecca Barnitz, York. Children: John W. (class of 1868); Charles E. (class of 1871), Edward G. (class of 1875); Mrs. M.L. Heisler; Mrs. J.A. Himes
Quantitative analysis of auxin sensing in leaf primordia argues against proposed role in regulating leaf dorsoventrality
Get PDFDorsoventrality in leaves has been shown to depend on the pre-patterned expression of KANADI and HD-ZIPIII genes within the plant shoot apical meristem (SAM). However, it has also been proposed that asymmetric auxin levels within initiating leaves help establish leaf polarity, based in part on observations of the DII auxin sensor. By analyzing and quantifying the expression of the R2D2 auxin sensor, we find that there is no obvious asymmetry in auxin levels during Arabidopsis leaf development. We further show that the mDII control sensor also exhibits an asymmetry in expression in developing leaf primordia early on, while it becomes more symmetric at a later developmental stage as reported previously. Together with other recent findings, our results argue against the importance of auxin asymmetry in establishing leaf polarity
- …
