41 research outputs found

    Nitrate modulates stem cell dynamics in Arabidopsis shoot meristems through cytokinins

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    The shoot apical meristem (SAM) is responsible for the generation of all the aerial parts of plants. Given its critical role, dynamical changes in SAM activity should play a central role in the adaptation of plant architecture to the environment. Using quantitative microscopy, grafting experiments, and genetic perturbations, we connect the plant environment to the SAM by describing the molecular mechanism by which cytokinins signal the level of nutrient availability to the SAM. We show that a systemic signal of cytokinin precursors mediates the adaptation of SAM size and organogenesis rate to the availability of mineral nutrients by modulating the expression of WUSCHEL, a key regulator of stem cell homeostasis. In time-lapse experiments, we further show that this mechanism allows meristems to adapt to rapid changes in nitrate concentration, and thereby modulate their rate of organ production to the availability of mineral nutrients within a few days. Our work sheds light on the role of the stem cell regulatory network by showing that it not only maintains meristem homeostasis but also allows plants to adapt to rapid changes in the environment

    Global Topological Order Emerges through Local Mechanical Control of Cell Divisions in the Arabidopsis Shoot Apical Meristem

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    The control of cell position and division act in concert to dictate multicellular organization in tissues and organs. How these processes shape global order and molecular movement across organs is an outstanding problem in biology. Using live 3D imaging and computational analyses, we extracted networks capturing cellular connectivity dynamics across the Arabidopsis shoot apical meristem (SAM) and topologically analyzed the local and global properties of cellular architecture. Locally generated cell division rules lead to the emergence of global tissue-scale organization of the SAM, facilitating robust global communication. Cells that lie upon more shorter paths have an increased propensity to divide, with division plane placement acting to limit the number of shortest paths their daughter cells lie upon. Cell shape heterogeneity and global cellular organization requires KATANIN, providing a multiscale link between cell geometry, mechanical cell-cell interactions, and global tissue order

    Million-year-scale alternation of warm–humid and semi-arid periods as a mid-latitude climate mode in the Early Jurassic (late Sinemurian, Laurasian Seaway)

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    Clay mineral and stable isotope (C, O) data are reported from the upper Sinemurian (Lower Jurassic) of the Cardigan Bay Basin (Llanbedr–Mochras Farm borehole, northwestern Wales) and the Paris Basin (Montcornet borehole, northern France) to highlight the prevailing environmental and climatic conditions. In both basins, located at similar palaeolatitudes of 30–35∘ N, the clay mineral assemblages comprise chlorite, illite, illite–smectite mixed layers (R1 I-S), smectite, and kaolinite in various proportions. Because the influence of burial diagenesis and authigenesis is negligible in both boreholes, the clay minerals are interpreted to be derived from the erosion of the Caledonian and Variscan massifs, including their basement and pedogenic cover. In the Cardigan Bay Basin, the variations in the proportions of smectite and kaolinite are inversely related to each other through the entire upper Sinemurian. As in the succeeding Pliensbachian, the upper Sinemurian stratigraphic distribution reveals an alternation of kaolinite-rich intervals reflecting strong hydrolysing conditions and smectite-rich intervals indicating a semi-arid climate. Kaolinite is particularly abundant in the upper part of the obtusum zone and in the oxynotum zone, suggesting more intense hydrolysing conditions likely coeval with warm conditions responsible for an acceleration of the hydrological cycle. In the north of the Paris Basin, the succession is less continuous compared to the Cardigan Bay Basin site, as the oxynotum zone and the upper raricostatum zone are either absent or highly condensed. The clay assemblages are dominantly composed of illite and kaolinite without significant stratigraphic trends, but a smectite-rich interval identified in the obtusum zone is interpreted as a consequence of the emersion of the London–Brabant Massif following a lowering of sea level. Following a slight negative carbon isotope excursion at the obtusum–oxynotum zone transition, a long-term decrease in ή13Corg from the late oxynotum–early raricostatum zones is recorded in the two sites and may precede or partly include the negative carbon isotope excursion of the Sinemurian–Pliensbachian Boundary Event, which is recognised in most basins worldwide and interpreted to signify a late pulse of the Central Atlantic Magmatic Province volcanism

    A MAP6-Related Protein Is Present in Protozoa and Is Involved in Flagellum Motility

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    In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function

    Evolution climatique au Jurassique inférieur (Sinémuriensupérieur) de la zone Nord-Ouest européenne, déduit de laminéralogie des argiles et des isotopes du carbone

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    National audienceL’étude des minĂ©raux argileux et des isotopes stables (carbone) du SinĂ©muriensupĂ©rieur du bassin de Cardigan Bay (forage de Mochras, Pays de Galles) et du bassinde Paris (forage de Montcornet, France) permet de mettre en Ă©vidence les conditionsenvironnementales et climatiques dominantes Ă  cette pĂ©riode. Dans les deux bassins,situĂ©s Ă  des palĂ©olatitudes proches (30 Ă  35°N), les assemblages de minĂ©raux argileuxcomprennent des chlorites, des illites, des interstratifiĂ©s illite-smectite (IS R1), dessmectites et des kaolinites dans des proportions variables. L'influence de la diagenĂšsed’enfouissement et de l'authigĂ©nĂšse Ă©tant nĂ©gligeable dans les deux forages, lesminĂ©raux argileux sont interprĂ©tĂ©s comme provenant principalement de l'Ă©rosion desmassifs calĂ©doniens et varisques. Dans le bassin de Cardigan Bay, les variations desproportions de smectites et de kaolinites sont opposĂ©es sur l'ensemble du SinĂ©muriensupĂ©rieur et rĂ©vĂšlent des intervalles d'hydrolyse intense sous un climat chaud etrĂ©guliĂšrement humide (fortes proportions de kaolinites) et des intervalles semi-arides(forte proportions de smectites). Les kaolinites, particuliĂšrement abondantes dans lapartie supĂ©rieure de la Zone Ă  obtusum et dans la Zone Ă  oxynotum, suggĂšrent unehydrolyse plus intenses probablement coĂŻncidente avec des conditions chaudes,responsables d'une accĂ©lĂ©ration du cycle hydrologique. Au nord du bassin de Paris, lasĂ©rie stratigraphique est beaucoup moins Ă©paisse que sur le site du bassin de CardiganBay. Les assemblages argileux sont principalement composĂ©s d'illites et de kaolinitessans tendance significative, mais un intervalle riche en smectites identifiĂ© dans la ZoneĂ  obtusum est interprĂ©tĂ© comme une consĂ©quence de l'Ă©mersion du Massif Londres-Brabant suite Ă  un abaissement du niveau marin. La diminution Ă  long terme du ÎŽ13CorgĂ  la fin de la Zone Ă  oxynotum, enregistrĂ©e dans les deux sites, semble amorcerl’excursion nĂ©gative reconnue quasi-mondialement au passageSinĂ©murien/Pliensbachien (SPBE) probablement liĂ©e au volcanisme de la ProvinceMagmatique de l'Atlantique Central (CAMP)
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