high-resolution-quantification-crystalline-cellulose-accumulation

High Resolution Quantification of Crystalline Cellulose Accumulation in <em>Arabidopsis</em> Roots to Monitor Tissue-specific Cell Wall Modifications

Plant cells are surrounded by a cell wall, the composition of which determines their final size and shape. The cell wall is composed of a complex matrix ...

Hebrew University of Jerusalem

The dispersal unit of wild wheat bears two pronounced awns that balance the unit as it falls. We discovered that the awns are also able to propel the seeds on and into the ground. The arrangement of cellulose fibrils causes bending of the awns with changes in humidity. Silicified hairs that cover the awns allow propulsion of the unit only in the direction of the seeds. This suggests that the dead tissue is analogous to a motor. Fueled by the daily humidity cycle, the awns induce the motility required for seed dispersal.

The role of wheat awns in the seed dispersal unit.

The dispersal unit of wild wheat bears two prominent filaments called awns. The awns bend as they dry and straighten in a damp environment. This hygroscopic movement is explained by the orientation of the cellulose fibrils that build the cell wall, as follows. The stiff fibrils are embedded in a soft hygroscopic matrix. When the cell wall dries, the matrix shrinks but the fibrils do not. Therefore, the cell wall contracts in a direction perpendicular to the fibril orientation. Using X-ray scattering we identified a region at the base of the awn that contains fibrils aligned in all directions. This is the active part, which contracts as it dries and pulls the awn to a bent position. Cryo-scanning electron microscopy revealed sequential laminas which are rotated to form a nano-scale plywood construction, implying planar local order within the global isotropy. Water molecules absorbed into the matrix probably cause large microscopic distortions by expanding neighboring layers in perpendicular directions. This is thought to cause opening of tiny gaps between fiber layers, to facilitate the exchange and the transport of water through the cell wall, and thereby to increase the sensitivity of the actuating unit to moderate changes in humidity.

Structures in the cell wall that enable hygroscopic movement of wheat awns.

The secondary plant cell wall is a composite of cellulose and a water-swelling matrix containing hemicelluloses and lignin. Recent experiments showed that this swelling capacity helps generating growth stresses, e.g., in conifer branches or in the stem when subjected to side loads. A similar mechanism also provides motility to wheat seeds. Here we study a simple mechanical model for the cell wall which--in contrast to earlier models--considers extensible cellulose fibrils in an isotropically swelling matrix. Depending on the detailed architecture of the cellulose fibrils, the model predicts that swelling may lead either to significant compressive or tensile stresses or to large movements at low stresses. The model reproduces most of the experimental observations in the wood cells and in the awns of wheat dispersal units. It is also simple enough to provide general guidelines for designing the architecture of fibres in an isotropic swelling medium to generate movements and forces of various kinds and directions.

Cellulose fibrils direct plant organ movements.

Awns are long, stiff filamentous extensions of glumes in many grasses. In wheat, awns contribute up to 40% of the grain's photosynthetic assimilates, and assist in seed dispersal. Awns accumulate silica in epidermal hairs and papillae, and silica has been positively associated with yield and environmental stress tolerance. Here, the awns of a set of domesticated wheat genotypes and their direct progenitor, Triticum turgidum ssp. dicoccoides were characterized. In addition, the silica concentration in awns was genetically dissected in a tetraploid wheat population of recombinant inbred lines (RILs) derived from a cross between durum wheat (cv. Langdon) and wild emmer (accession G18-16). Scanning electron micrographs revealed a continuous silica layer under the cuticle. Extended silicification was identified in the epidermis cell wall and in sclerenchyma cells near the vascular bundles, but not in the stomata, suggesting that an active process directs the soluble silica away from the water evaporation stream. The number of silicified cells was linearly correlated to silica concentration in dry weight (DW), suggesting cellular control over silicification. Domesticated wheat awns contained up to 19% silica per DW, as compared with 7% in the wild accessions, suggesting selection pressure associated with the domestication process. Six quantitative trait loci (QTLs) for silica were identified in the awns, with a LOD score of 3.7-6.3, three of which overlapped genomic regions that contribute to high grain protein. Localization of silica in the awns and identification of QTLs help illuminate mechanisms associated with silica metabolism in wheat.

Genetic control over silica deposition in wheat awns.

Plant biomineralization involves calcium and silicon transport and mineralization. Respective analytical methods and case studies are listed. Calcium carbonate is deposited in cystoliths, calcium oxalate in idioblasts. Silicon is deposited in phytoliths. Biomineralization is a coordinated process.

Calcium and silicon mineralization in land plants: transport, structure and function.

The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork's bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.

Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn.

Many plant tissues and organs are capable of moving due to changes in the humidity of the environment, such as the opening of the seed capsule of the ice plant and the opening of the pine cone. These are fascinating examples for the materials engineer, as these tissues are non-living and move solely through the differential swelling of anisotropic tissues and in principle may serve as examples for the bio-inspired design of artificial actuators. In this paper, we model the microstructure of the wild wheat awn (Triticum turgidum ssp. dicoccoides) by finite elements, especially focusing on the specific microscopic features of the active part of the awn. Based on earlier experimental findings, cell walls are modeled as multilayered cylindrical tubes with alternating cellulose fiber orientation in successive layers. It is shown that swelling upon hydration of this system leads to the formation of gaps between the layers, which could act as valves, thus enabling the entry of water into the cell wall. This supports the hypothesis that this plywood-like arrangement of cellulose fibrils enhances the effect of ambient humidity by accelerated water or vapor diffusion along the gaps. The finite element model shows that a certain distribution of axially and tangentially oriented fibers is necessary to generate sufficient tensile stresses within the cell wall to open nanometer-sized gaps between cell wall layers.

Finite element modeling of the cyclic wetting mechanism in the active part of wheat awns.

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&#x81EA;&#x767A;&#x7684;&#x306A;&#x306D;&#x3058;&#x308C;&#x3068;&#x975E;&#x30E6;&#x30FC;&#x30AF;&#x30EA;&#x30C3;&#x30C9;&#x306E;&#x68D2;&#x3067;&#x66F2;&#x7387;&#x306E;&#x51FA;&#x73FE;: Erodium &#x690D;&#x7269;&#x7D30;&#x80DE;&#x3078;&#x306E;&#x5FDC;&#x7528;&#x3002;

&#x6211;&#x4EEC;&#x76EE;&#x524D;&#x8584;&#x975E;&#x6B27;&#x51E0;&#x91CC;&#x5FB7;&#x7684;&#x5F39;&#x6027;&#x6746;&#x7684;&#x9650;&#x5236;&#x6A21;&#x5F0F;&#x3002;&#x6211;&#x4EEC;&#x6765;&#x81EA;&#x4E09;&#x7EF4; (3D) &#x53C2;&#x8003;&#x516C;&#x5236;&#x7684;&#x6746;&#xFF0C;&#x662F;&#x7531;&#x5176;&#x5185;&#x90E8;&#x7684;&#x7269;&#x8D28;&#x7ED3;&#x6784;&#xFF0C;&#x63A8;&#x5BFC;&#x51FA; 1 (D) &#x51CF;&#x5C11;&#x6746;&#x7406;&#x8BBA;&#x3002;&#x5177;&#x4F53;&#x800C;&#x8A00;&#xFF0C;&#x6211;&#x4EEC;&#x663E;&#x793A;&#x7684;&#x81EA;&#x53D1;&#x7684;&#x9EBB;&#x82B1;&#x548C;&#x6746;&#x7684;&#x66F2;&#x7387;&#x5982;&#x4F55;&#x6446;&#x8131;&#x53C2;&#x8003;&#x516C;&#x5236;&#x884D;&#x751F;&#x54C1;&#x3002;&#x56E0;&#x6B64;&#xFF0C;&#x8BE5;&#x6A21;&#x578B;&#x5141;&#x8BB8;&#x8BA1;&#x7B97;&#x7EC6;&#x6746;&#x76F4;&#x63A5;&#x4ECE;&#x5176;&#x5185;&#x90E8;&#x7ED3;&#x6784;&#x7684;&#x65E0;&#x7EA6;&#x675F;&#x7684;&#x5747;&#x8861;&#x914D;&#x7F6E;&#x3002;&#x4ECE; Geraniaceae &#x690D;&#x7269;&#x5BB6;&#x4EBA;&#x548C;&#x8131;&#x6C34;&#x6784;&#x578B;&#x54CD;&#x5E94;&#x6A21;&#x578B;&#x5E94;&#x7528;&#x5230;&#x7EC6;&#x80DE;&#x7684;&#x7814;&#x7A76;&#x3002;&#x6211;&#x4EEC;&#x5C55;&#x793A;&#x5982;&#x4F55;&#x5BF9;&#x7EC6;&#x80DE;&#x58C1;&#x7684;&#x7EA4;&#x7EF4;&#x7D20;&#x7EA4;&#x7EF4;&#x7684;&#x51E0;&#x4F55;&#x5B89;&#x6392;&#x786E;&#x5B9A;&#x87BA;&#x65CB;&#x5F62;&#x72B6;&#x7684;&#x5B64;&#x7ACB;&#x7684;&#x5355;&#x5143;&#x683C;&#x3002;

&#x51FA;&#x73B0;&#x4E86;&#x81EA;&#x53D1;&#x7684;&#x9EBB;&#x82B1;&#x548C;&#x66F2;&#x7387;&#x7684;&#x975E;&#x6B27;&#x51E0;&#x91CC;&#x5FB7;&#x68D2;&#xFF1A; &#x8001;&#x690D;&#x7269;&#x7EC6;&#x80DE;&#x4E2D;&#x7684;&#x5E94;&#x7528;&#x3002;

We present a limiting model for thin non-euclidean elastic rods. Originating from the three-dimensional (3D) reference metric of the rod, which is determined by its internal material structure, we derive a 1D reduced rod theory. Specifically, we show how the spontaneous twist and curvature of a rod emerge from the reference metric derivatives. Thus, the model allows calculating the unconstrained equilibrium configuration of a thin rod directly from its internal structure. The model is applied to the study of cells from members of the Geraniaceae plant family and their configurational response to dehydration. We show how the geometrical arrangement of cellulose fibrils on the cell walls determines the helical shapes of isolated cells.

Emergence of spontaneous twist and curvature in non-euclidean rods: application to Erodium plant cells.

Nous pr&eacute;sentons un mod&egrave;le limite de minces tiges &eacute;lastiques non euclidienne. Originaire de la m&eacute;trique de r&eacute;f&eacute;rence &agrave; trois dimensions (3D) de la tige, qui est d&eacute;termin&eacute;e par sa structure interne des mat&eacute;riaux, nous d&eacute;rivons une th&eacute;orie de tige 1D r&eacute;duit. Plus pr&eacute;cis&eacute;ment, nous montrons comment la torsion spontan&eacute;e et la courbure d&#39;une tige sortent les d&eacute;riv&eacute;s m&eacute;triques de r&eacute;f&eacute;rence. Ainsi, le mod&egrave;le permet de calculer la configuration d&#39;&eacute;quilibre sans contrainte d&#39;une tige mince directement &agrave; partir de sa structure interne. Le mod&egrave;le est appliqu&eacute; &agrave; l&#39;&eacute;tude des cellules des membres de la famille des G&eacute;raniac&eacute;es et leur r&eacute;ponse configurationnelle &agrave; la d&eacute;shydratation. Nous montrons comment la disposition g&eacute;om&eacute;trique des fibrilles de cellulose sur les murs de la cellule d&eacute;termine la forme h&eacute;lico&iuml;dale des cellules isol&eacute;es.

&Eacute;mergence de torsion spontan&eacute;e et courbure dans les tiges non euclidienne : application aux cellules v&eacute;g&eacute;tales Erodium.

Wir pr&auml;sentieren ein begrenzender Modell f&uuml;r d&uuml;nne nichteuklidische elastische St&auml;be. Aus der dreidimensionalen (3D) Referenz-Metrik des Stabes, der durch seine interne materielle Struktur bestimmt wird, leiten wir eine 1D reduziert-Stab-Theorie. Insbesondere zeigen wir, wie die spontanen Dreh und Kr&uuml;mmung der ein Stab aus dem metrischen Referenz-Derivaten hervorgehen. So erlaubt das Modell berechnen die zwanglose Gleichgewicht-Konfiguration von einem d&uuml;nnen Stab direkt von ihrer internen Struktur. Das Modell wird von Mitgliedern der Familie der Storchschnabelgew&auml;chse und ihre Konfiguration betreffenden Reaktion auf Dehydrierung zum Studium der Zellen angewendet. Wir zeigen, wie die geometrische Anordnung der Zellulose F&auml;serchen auf die Zellw&auml;nde die Spiralige Formen der isolierten Zellen bestimmt.

Entstehung von spontanen Dreh und Kr&uuml;mmung in nichteuklidischen Stangen: Anwendung auf Reiherschn&auml;bel Pflanzenzellen.

Vi presentiamo un modello limito per sottili canne elastici non-euclidee. Provenienti dalla metrica di riferimento tridimensionale (3D) dell&#39;asta, che &egrave; determinato dalla sua struttura interna del materiale, deriviamo una teoria di rod 1 D ridotto. In particolare, ci mostra come la torsione spontanea e curvatura di una canna emergono dai derivati di riferimento metrico. Cos&igrave;, il modello permette di calcolare la configurazione di equilibrio senza vincoli di un&#39;asta sottile direttamente dalla sua struttura interna. Il modello viene applicato allo studio delle cellule da membri della famiglia Geraniaceae pianta e loro risposta configurazionale a disidratazione. Vi mostriamo come la disposizione geometrica delle fibrille di cellulosa sulle pareti della cellula determina le forme elicoidali di cellule isolate.

Emersione spontanea torsione e curvatura in coni retinici non-euclidee: applicazione di cellule vegetali Erodium.

&#xC587;&#xC740; &#xC720;&#xD074;&#xB9AC;&#xB4DC; &#xD0C4;&#xB825; &#xBD09; &#xC81C;&#xD55C; &#xBAA8;&#xB378;&#xC744; &#xC18C;&#xAC1C;&#xD569;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC; 1 D &#xAC10;&#xC18C; &#xB85C;&#xB4DC; &#xC774;&#xB860; &#xD30C;&#xC0DD;&#xC758; &#xB0B4;&#xBD80; &#xC790;&#xB8CC; &#xAD6C;&#xC870;&#xC5D0; &#xC758;&#xD574; &#xACB0;&#xC815; &#xB418;&#xB294; &#xB9C9;&#xB300;&#xC758; 3 &#xCC28;&#xC6D0; (3D) &#xCC38;&#xC870; &#xD1B5;&#xACC4;&#xC5D0;&#xC11C; &#xBC1C;&#xC0DD; &#xD558;&#xB294;. &#xD2B9;&#xD788; &#xC6B0;&#xB9AC; &#xC790;&#xBC1C;&#xC801;&#xC778; &#xD2B8;&#xC704;&#xC2A4;&#xD2B8;&#xC640; &#xB9C9;&#xB300;&#xC758; &#xACE1;&#xB960; &#xCC38;&#xC870; &#xD1B5;&#xACC4; &#xD30C;&#xC0DD; &#xC0C1;&#xD488;&#xC5D0;&#xC11C; &#xB4F1;&#xC7A5; &#xD558;&#xB294; &#xBC29;&#xBC95;&#xC744; &#xBCF4;&#xC5EC; &#xC90D;&#xB2C8;&#xB2E4;. &#xB530;&#xB77C;&#xC11C;, &#xBAA8;&#xB378;&#xC758; &#xB0B4;&#xBD80; &#xAD6C;&#xC870;&#xC5D0;&#xC11C; &#xC9C1;&#xC811; &#xC587;&#xC740; &#xB9C9;&#xB300;&#xC758; &#xADE0;&#xD615;&#xC744; &#xBB34;&#xC81C;&#xD55C; &#xAD6C;&#xC131;&#xC744; &#xACC4;&#xC0B0; &#xC218; &#xC788;&#xC2B5;&#xB2C8;&#xB2E4;. &#xBAA8;&#xB378; Geraniaceae &#xACF5;&#xC7A5; &#xAC00;&#xC871; &#xD68C;&#xC6D0; configurational &#xD0C8;&#xC218; &#xBC18;&#xC751;&#xC5D0;&#xC11C;&#xC5D0;&#xC11C; &#xC138;&#xD3EC;&#xC758; &#xC5F0;&#xAD6C;&#xC5D0; &#xC801;&#xC6A9; &#xB429;&#xB2C8;&#xB2E4;. &#xC6B0;&#xB9AC; &#xC138;&#xD3EC; &#xBCBD;&#xC5D0; &#xC140; &#xB8F0; &#xB85C;&#xC2A4; &#xC18C;&#xC758; &#xAE30;&#xD558;&#xD559;&#xC801; &#xBC30;&#xC5F4; &#xACA9;&#xB9AC; &#xB41C; &#xC140;&#xC758; &#xB098;&#xC120;&#xD615; &#xBAA8;&#xC591;&#xC744; &#xACB0;&#xC815; &#xD558;&#xB294; &#xBC29;&#xBC95;&#xC744; &#xBCF4;&#xC5EC; &#xC90D;&#xB2C8;&#xB2E4;.

&#xC790;&#xBC1C;&#xC801;&#xC778; &#xD2B8;&#xC704;&#xC2A4;&#xD2B8;&#xC640; &#xC720;&#xD074;&#xB9AC;&#xB4DC; &#xBD09;&#xC5D0;&#xC11C; &#xACE1;&#xB960;&#xC758; &#xCD9C;&#xD604;: Erodium &#xC2DD;&#xBB3C; &#xC138;&#xD3EC; &#xC751;&#xC6A9;.

Presentamos un modelo limitante para delgadas barras el&aacute;sticos no-euclidiana. Originarios de la m&eacute;trica tridimensional (3D) referencia de la barra, que est&aacute; determinada por su estructura interna del material, derivamos una teor&iacute;a de barra 1D reducido. Espec&iacute;ficamente, nos muestran c&oacute;mo el toque espont&aacute;neo y curvatura de una varilla emergen de los derivados de m&eacute;tricas de referencia. As&iacute;, el modelo permite calcular la configuraci&oacute;n de equilibrio sin restricciones de una varilla fina directamente en su estructura interna. El modelo se aplica al estudio de las c&eacute;lulas de los miembros de la familia Geraniaceae de la planta y su respuesta basada en la configuraci&oacute;n a la deshidrataci&oacute;n. Mostramos c&oacute;mo el arreglo geom&eacute;trico de las fibrillas de celulosa en las paredes celulares determina las formas helicoidales de c&eacute;lulas aisladas.

Aparici&oacute;n de las torsiones espont&aacute;nea y curvatura en barras no-Euclidiana: aplicaci&oacute;n a c&eacute;lulas de la planta de Erodium.

The cell walls constitute the mechanical support of plants. Crystalline cellulose building the walls forms rigid microfibrils that set the stiffness of the cell and the direction in which it expands during growth. Therefore, the determination of the directions of the microfibrils is important in both mechanical and developmental assays. We adapted polarized light microscopy to estimate the cellulose microfibril orientations at subcellular resolution. The optical information supplements X-ray scattering data, Raman microspectroscopy, and electron microscopy. We analyzed samples from three plant tissues: cells from an Araucaria excels branch, in which we revealed lower cellulose density in regions where the cell wall curvature becomes bigger, namely, the cell wall corners; a wheat (Triticum turgidum) awn's hygroscopically active region, which revealed a gradient in the cellulose microfibril angles that spans across four cell rows; and a stork's bill's (Erodium gruinum) coiling awn, which revealed that the cellulose in the cell wall is organized in two orientations seamed together, rather than in a continuous helix. The unique spatial information is easily obtained from microscopic specimens and further illuminates new aspects in the mechanical tissues.

Quantification of microfibril angle in secondary cell walls at subcellular resolution by means of polarized light microscopy.

The family Geraniaceae is characterized by a beak-like fruit, consisting of five seeds appended by a tapering awn. The awns exhibit coiling or bending hygroscopic movement as part of the seed dispersal strategy. Here we explain the variation in the hygroscopic reaction based on structural principles. We examined five representative species from three genera: Erodium, Geranium, and Pelargonium. Using X-ray diffraction, and electron and polarized light microscopy, we measured the cellulose microfibril angles in relation to the cell and cellulose helix axes. The behavior of separated single cells during dehydration was also examined. A bi-layered structure characterizes all the representative genera studied, with a hygroscopically contracting inner layer, and a stiff outer layer. We found that the cellulose arrangement in the inner layer is responsible for the type of awn deformation (coiling or bending). In three of the five awns examined, we identified an additional coiling outer sublayer, which adds coiling deformation to the awn. We divide the movements into three types: bending, coiling, and coiled-bending. All movement types are found in the Geranium genus. These characteristics are of importance for understanding the evolution of seed dispersal mechanisms in the Geraniaceae family.

Hygroscopic movements in Geraniaceae: the structural variations that are responsible for coiling or bending.

Coherent plant growth requires spatial integration of hormonal pathways and cell wall remodeling activities. However, the mechanisms governing sensitivity to hormones and how cell wall structure integrates with hormonal effects are poorly understood. We found that coordination between two types of epidermal root cells, hair and nonhair cells, establishes root sensitivity to the plant hormones brassinosteroids (BRs). While expression of the BR receptor BRASSINOSTEROID-INSENSITIVE1 (BRI1) in hair cells promotes cell elongation in all tissues, its high relative expression in nonhair cells is inhibitory. Elevated ethylene and deposition of crystalline cellulose underlie the inhibitory effect of BRI1. We propose that the relative spatial distribution of BRI1, and not its absolute level, fine-tunes growth.

Root growth is modulated by differential hormonal sensitivity in neighboring cells.

As non-motile organisms, plants develop means to spread their progenies. Hygroscopic movement is a very common mechanism employed in seed dispersal. This type of movement is created when the tissue desiccates and the cell walls dry and shrink. A contraction force develops, the direction and strength of which depends on the architecture of the tissue. This force may be utilized for a simple release of seeds, their catapultion, and for pushing seeds along the soil to a germination locus. We review the formation of a bend, a twist and a coil within various dispersal apparatuses as a reaction to the dehydration of the tissue. We compare the microscopic structures of hygroscopic devices supporting slow or fast movement, adaptations to dry or wet climates, and single use versus repeated movement. We discuss the development of the disconnecting tissues in relation to the development of a hygroscopic mechanism. As plant cultivation is dependent on seed dispersal control, we demonstrate that during the domestication of sesame and wheat, seed dispersal is avoided not due to a defective hygroscopic tissue, but rather a missing dehiscence tissue. Seed dispersal is a crucial stage in the life cycle of plants. Thus, hygroscopic movement plays a central part in plant ecology and agriculture.

Insights into the microstructures of hygroscopic movement in plant seed dispersal.

Differentiation of the maternally derived seed coat epidermal cells into mucilage secretory cells is a common adaptation in angiosperms. Recent studies identified cellulose as an important component of seed mucilage in various species. Cellulose is deposited as a set of rays that radiate from the seed upon mucilage extrusion, serving to anchor the pectic component of seed mucilage to the seed surface. Using transcriptome data encompassing the course of seed development, we identified COBRA-LIKE2 (COBL2), a member of the glycosylphosphatidylinositol-anchored COBRA-LIKE gene family in Arabidopsis (Arabidopsis thaliana), as coexpressed with other genes involved in cellulose deposition in mucilage secretory cells. Disruption of the COBL2 gene results in substantial reduction in the rays of cellulose present in seed mucilage, along with an increased solubility of the pectic component of the mucilage. Light birefringence demonstrates a substantial decrease in crystalline cellulose deposition into the cellulosic rays of the cobl2 mutants. Moreover, crystalline cellulose deposition into the radial cell walls and the columella appears substantially compromised, as demonstrated by scanning electron microscopy and in situ quantification of light birefringence. Overall, the cobl2 mutants display about 40% reduction in whole-seed crystalline cellulose content compared with the wild type. These data establish that COBL2 plays a role in the deposition of crystalline cellulose into various secondary cell wall structures during seed coat epidermal cell differentiation.

COBRA-LIKE2, a member of the glycosylphosphatidylinositol-anchored COBRA-LIKE family, plays a role in cellulose deposition in arabidopsis seed coat mucilage secretory cells.

Induction of adventitious roots (ARs) in recalcitrant plants often culminates in cell division and callus formation rather than root differentiation. Evidence is provided here to suggest that microtubules (MTs) play a role in the shift from cell division to cell differentiation during AR induction. First, it was found that fewer ARs form in the temperature-sensitive mutant mor1-1, in which the MT-associated protein MOR1 is mutated, and in bot1-1, in which the MT-severing protein katanin is mutated. In the two latter mutants, MT dynamics and form are perturbed. By contrast, the number of ARs increased in RIC1-OX3 plants, in which MT bundling is enhanced and katanin is activated. In addition, any1 plants in which cell walls are perturbed made more ARs than wild-type plants. MT perturbations during AR induction in mor1-1 or in wild-type hypocotyls treated with oryzalin led to the formation of amorphous clusters of cells reminiscent of callus. In these cells a specific pattern of polarized light retardation by the cell walls was lost. PIN1 polarization and auxin maxima were hampered and differentiation of the epidermis was inhibited. It is concluded that a fine-tuned crosstalk between MTs, cell walls, and auxin transport is required for proper AR induction.

Dissecting the contribution of microtubule behaviour in adventitious root induction.

A silicon transporter homolog was upregulated by Si fertilization and drought in potato roots and leaves. High Si in tuber skin resulted in anatomical and compositional changes suggesting delayed skin maturation. Silicon (Si) fertilization has beneficial effects on plant resistance to biotic and abiotic stresses. Potatoes, low Si accumulators, are susceptible to yield loss due to suboptimal growth conditions; thus Si fertilization may contribute to crop improvement. The effect of Si fertilization on transcript levels of putative transporters, Si uptake and tuber quality was studied in potatoes grown in a glasshouse and fertilized with sodium silicate, under normal and drought-stress conditions. Anatomical studies and Raman spectroscopic analyses of tuber skin were conducted. A putative transporter, StLsi1, with conserved amino acid domains for Si transport, was isolated. The StLsi1 transcript was detected in roots and leaves and its level increased twofold following Si fertilization, and about fivefold in leaves upon Si × drought interaction. Nevertheless, increased Si accumulation was detected only in tuber peel of Si-fertilized plants--probably due to passive movement of Si from the soil solution--where it modified skin cell morphology and cell-wall composition. Compared to controls, skin cell area was greater, suberin biosynthetic genes were upregulated and skin cell walls were enriched with oxidized aromatic moieties suggesting enhanced lignification and suberization. The accumulating data suggest delayed tuber skin maturation following Si fertilization. Despite StLsi1 upregulation, low accumulation of Si in roots and leaves may result from low transport activity. Study of Si metabolism in potato, a major staple food, would contribute to the improvement of other low Si crops to ensure food security under changing climate.

Silicon fertilization of potato: expression of putative transporters and tuber skin quality.

Screening large populations for carriers of known or de novo rare SNPs is required both in Targeting induced local lesions IN genomes (TILLING) experiments in plants and analogously in screening human populations. We previously suggested an approach that combines the celebrated mathematical field of compressed sensing with next-generation sequencing to allow such large-scale screening. Based on pooled measurements, this method can identify multiple carriers of heterozygous or homozygous rare alleles while using only a small fraction of resources. Its rigorous mathematical foundations allow scalable and robust detection and provide error correction and resilience to experimental noise. This study presents a large scale experimental demonstration of our computational approach in which we target a TILLING population of 1024 Sorghum bicolor lines to detect carriers of de novo SNPs whose frequency was less than 0.1%, using only 48 pools. Subsequent validation has confirmed that all detected lines were indeed carriers of the predicted mutations. This novel approach adds a highly cost-effective and robust tool for biologists and breeders to allow identification of novel alleles and subsequent functional analysis. This article is protected by copyright. All rights reserved.

Article	Year
The role of wheat awns in the seed dispersal unit. Science (New York, N.Y.)\| PubMed ID: 17495170	2007
Structures in the cell wall that enable hygroscopic movement of wheat awns. Journal of structural biology\| PubMed ID: 18625323	2008
Cellulose fibrils direct plant organ movements. Faraday discussions\| PubMed ID: 19049001	2008
Genetic control over silica deposition in wheat awns. Physiologia plantarum\| PubMed ID: 20444192	2010
Calcium and silicon mineralization in land plants: transport, structure and function. Plant science : an international journal of experimental plant biology\| PubMed ID: 21497710	2011
Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn. Journal of the Royal Society, Interface / the Royal Society\| PubMed ID: 21865252	2012
Finite element modeling of the cyclic wetting mechanism in the active part of wheat awns. Biointerphases\| PubMed ID: 22791359	2012
Emergence of spontaneous twist and curvature in non-euclidean rods: application to Erodium plant cells. Physical review letters\| PubMed ID: 23003997	2012
Quantification of microfibril angle in secondary cell walls at subcellular resolution by means of polarized light microscopy. The New phytologist\| PubMed ID: 23240639	2013
Hygroscopic movements in Geraniaceae: the structural variations that are responsible for coiling or bending. The New phytologist\| PubMed ID: 23574364	2013
Root growth is modulated by differential hormonal sensitivity in neighboring cells. Genes & development\| PubMed ID: 24736847	2014
Insights into the microstructures of hygroscopic movement in plant seed dispersal. Plant science : an international journal of experimental plant biology\| PubMed ID: 24767122	2014
COBRA-LIKE2, a member of the glycosylphosphatidylinositol-anchored COBRA-LIKE family, plays a role in cellulose deposition in arabidopsis seed coat mucilage secretory cells. Plant physiology\| PubMed ID: 25583925	2015
Dissecting the contribution of microtubule behaviour in adventitious root induction. Journal of experimental botany\| PubMed ID: 25788735	2015
Silicon fertilization of potato: expression of putative transporters and tuber skin quality. Planta\| PubMed ID: 26384982	2016
Highly efficient de novo mutant identification in a Sorghum bicolor TILLING population using the ComSeq approach. The Plant journal : for cell and molecular biology\| PubMed ID: 26959378	2016

Rivka Elbaum

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