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      Towards an understanding of spiral patterning in the Sargassum muticum shoot apex

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      Scientific Reports
      Nature Publishing Group UK

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          Abstract

          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; 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° angle) and an unlinked apical cell division pattern. The Sargassum apex presents characteristics of a self-organising system, similar to plant meristems. In contrast to complex 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.

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          Biological interactions between polysaccharides and divalent cations: The egg-box model

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            Pectin-induced changes in cell wall mechanics underlie organ initiation in Arabidopsis.

            Tissue mechanics have been shown to play a key role in the regulation of morphogenesis in animals [1-4] and may have an equally important role in plants [5-9]. The aerial organs of plants are formed at the shoot apical meristem following a specific phyllotactic pattern [10]. The initiation of an organ from the meristem requires a highly localized irreversible surface deformation, which depends on the demethylesterification of cell wall pectins [11]. Here, we used atomic force microscopy (AFM) to investigate whether these chemical changes lead to changes in tissue mechanics. By mapping the viscoelasticity and elasticity in living meristems, we observed increases in tissue elasticity, correlated with pectin demethylesterification, in primordia and at the site of incipient organs. Measurements of tissue elasticity at various depths showed that, at the site of incipient primordia, the first increases occurred in subepidermal tissues. The results support the following causal sequence of events: (1) demethylesterification of pectin is triggered in subepidermal tissue layers, (2) this contributes to an increase in elasticity of these layers-the first observable mechanical event in organ initiation, and (3) the process propagates to the epidermis during the outgrowth of the organ. Copyright © 2011 Elsevier Ltd. All rights reserved.
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              Epibacterial community patterns on marine macroalgae are host-specific but temporally variable.

              Marine macroalgae are constantly exposed to epibacterial colonizers. The epiphytic bacterial patterns and their temporal and spatial variability on host algae are poorly understood. To investigate the interaction between marine macroalgae and epiphytic bacteria, this study tested if the composition of epibacterial communities on different macroalgae was specific and persisted under varying biotic and abiotic environmental conditions over a 2-year observation time frame. Epibacterial communities on the co-occurring macroalgae Fucus vesiculosus, Gracilaria vermiculophylla and Ulva intestinalis were repeatedly sampled in summer and winter of 2007 and 2008. The epibacterial community composition was analysed by denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene libraries. Epibacterial community profiles did not only differ significantly at each sampling interval among algal species, but also showed consistent seasonal differences on each algal species at a bacterial phylum level. These compositional patterns re-occurred at the same season of two consecutive years. Within replicates of the same algal species, the composition of bacterial phyla was subject to shifts at the bacterial species level, both within the same season but at different years and between different seasons. However, 7-16% of sequences were identified as species specific to the host alga. These findings demonstrate that marine macroalgae harbour species-specific and temporally adapted epiphytic bacterial biofilms on their surfaces. Since several algal host-specific bacteria were highly similar to other bacteria known to either avoid subsequent colonization by eukaryotic larvae or to exhibit potent antibacterial activities, algal host-specific bacterial associations are expected to play an important role for marine macroalgae. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.
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                Author and article information

                Contributors
                siobhanb@ucla.edu
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                24 October 2017
                24 October 2017
                2017
                : 7
                : 13887
                Affiliations
                [1 ]ISNI 0000000121885934, GRID grid.5335.0, The Sainsbury Laboratory, , University of Cambridge, ; Bateman Street, Cambridge, CB2 1LR UK
                [2 ]ISNI 0000 0000 9632 6718, GRID grid.19006.3e, Molecular, Cell and Developmental Biology, UCLA, ; 610 Charles E Young Dr East, Los Angeles, CA 90095-7239 USA
                Author information
                http://orcid.org/0000-0002-4308-5580
                Article
                13767
                10.1038/s41598-017-13767-5
                5654765
                29066850
                5c6365c8-bfd6-4570-b94b-601740e5dcb3
                © The Author(s) 2017

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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                : 19 July 2017
                : 26 September 2017
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