Organization Of Cellulose Microfibrils Research Articles

Single Molecule Analysis of the Arabidopsis FRA1 Kinesin Shows that It Is a Functional Motor Protein with Unusually High Processivity

The Arabidopsis FRA1 kinesin contributes to the organization of cellulose microfibrils through an unknown mechanism. The cortical localization of this kinesin during interphase raises the possibility that it transports cell wall-related cargoes along cortical microtubules that either directly or indirectly influence cellulose microfibril patterning. To determine whether FRA1 is an authentic motor protein, we combined bulk biochemical assays and single molecule fluorescence imaging to analyze the motor properties of recombinant, GFP-tagged FRA1 containing the motor and coiled-coil domains (designated as FRA1(707)-GFP). We found that FRA1(707)-GFP binds to microtubules in an ATP-dependent manner and that its ATPase activity is dramatically stimulated by the presence of microtubules. Using single molecule studies, we found that FRA1(707)-GFP moves processively along microtubule tracks at a velocity of about 0.4 μm s(-1). In addition, we found that FRA1(707)-GFP is a microtubule plus-end-directed motor and that it moves along microtubules as a dimer. Interestingly, our single molecule analysis shows that the processivity of FRA1(707)-GFP is at least twice the processivity of conventional kinesin, making FRA1 the most processive kinesin to date. Together, our data show that FRA1 is a bona fide motor protein that has the potential to drive long-distance transport of cargo along cortical microtubules.

Cell proliferation, cell shape, and microtubule and cellulose microfibril organization of tobacco BY-2 cells are not altered by exposure to near weightlessness in space

The microtubule cytoskeleton and the cell wall both play key roles in plant cell growth and division, determining the plant’s final stature. At near weightlessness, tubulin polymerizes into microtubules in vitro, but these microtubules do not self-organize in the ordered patterns observed at 1g. Likewise, at near weightlessness cortical microtubules in protoplasts have difficulty organizing into parallel arrays, which are required for proper plant cell elongation. However, intact plants do grow in space and therefore should have a normally functioning microtubule cytoskeleton. Since the main difference between protoplasts and plant cells in a tissue is the presence of a cell wall, we studied single, but walled, tobacco BY-2 suspension-cultured cells during an 8-day space-flight experiment on board of the Soyuz capsule and the International Space Station during the 12S mission (March–April 2006). We show that the cortical microtubule density, ordering and orientation in isolated walled plant cells are unaffected by near weightlessness, as are the orientation of the cellulose microfibrils, cell proliferation, and cell shape. Likely, tissue organization is not essential for the organization of these structures in space. When combined with the fact that many recovering protoplasts have an aberrant cortical microtubule cytoskeleton, the results suggest a role for the cell wall, or its production machinery, in structuring the microtubule cytoskeleton.

Arabidopsis cortical microtubules position cellulose synthase delivery to the plasma membrane and interact with cellulose synthase trafficking compartments

Plant cell morphogenesis relies on the organization and function of two polymer arrays separated by the plasma membrane: the cortical microtubule cytoskeleton and cellulose microfibrils in the cell wall. Studies using in vivo markers confirmed that one function of the cortical microtubule array is to drive organization of cellulose microfibrils by guiding the trajectories of active cellulose synthase (CESA) complexes in the plasma membrane, thus orienting nascent microfibrils. Here we provide evidence that cortical microtubules also position the delivery of CESA complexes to the plasma membrane and interact with small CESA-containing compartments by a mechanism that permits motility driven by microtubule depolymerization. The association of CESA compartments with cortical microtubules was greatly enhanced during osmotic stress and other treatments that limit cellulose synthesis. On recovery from osmotic stress, delivery of CESA complexes to the plasma membrane was observed in association with microtubule-tethered compartments. These results reveal multiple functions for the microtubule cortical array in organizing CESA in the cell cortex.

Plants control the properties and actuation of their organs through the orientation of cellulose fibrils in their cell walls

Plants use the orientation of cellulose microfibrils to create cell walls with anisotropic properties related to specific functions. This enables organisms to control the shape and size of cells during growth, to adjust the mechanical performance of tissues, and to perform bending movements of organs. We review the key function of cellulose orientation in defining structural-functional relationships in cell walls from a biomechanics perspective, and illustrate this by examples mainly from our own work. First, primary cell-wall expansion largely depends on the organization of cellulose microfibrils in newly deposited tissue and model calculations allow an estimate of how their passive re-orientation may influence the growth of cells. Moreover, mechanical properties of secondary cell walls depend to a large extent on the orientation of cellulose fibrils and we discuss strategies whereby plants utilize this interrelationship for adaptation. Lastly, we address the question of how plants regulate complex organ movements by designing appropriate supramolecular architectures at the level of the cell wall. Several examples, from trees to grasses, show that the cellulose architecture in the cell wall may be used to direct the swelling or shrinking of cell walls and thereby generate internal growth stress or movement of organs.

Ethylene is a modulator of gibberellic acid-induced antheridiogenesis in Anemia phyllitidis gametophytes

In fern (Anemia phyllitidis) gametophytes cellulose in the walls of the antheridial zone cells which was organized in clusters and spots was transformed via dispersed form to fibrillar arrangement (layered in oblique and perpendicular array in relation to the transverse direction of cell expansion) during antheridiogenesis induced by gibberellic acid (GA3) and/or enhanced by 1-aminocyclopropane-1-carboxylic acid (ACC). In the ACC-treated gametophytes, where antheridia were not induced, the cellulose was arranged in the same manner. Aminooxyacetic acid (AOA), which inhibits antheridiogenesis and development of fern gametophytes, produced in the cell walls both random and longitudinal type of organization of cellulose microfibrils, however, in the GA3/AOA-treated plants the oblique type was also observed. The total numbers of cells with perpendicular and/or oblique type of cellulose microfibrils in the GA3-, GA3/ACC-and GA3/AOA-treated gametophytes corresponded to the average number of antheridia formed. Moreover, it was found that the extracts from the gametophytes treated with GA3 or with the mixture of GA3 and ACC contained significantly less soluble sugars but more α-amylase-and endoglucanase-released sugars than the extracts from the gametophytes of the other series. Thin layer chromatography of the samples from the cell wall extracts hydrolyzed by endoglucanase contained xylose and cellobiose which suggested that these sugars built the xyloglucans, hemicellulose polymers responsible for tethering of walls of fern gametophyte cells like in higher plants.

Dual-axis electron tomography: a new approach for investigating the spatial organization of wood cellulose microfibrils

We have employed dual-axis electron tomography to investigate the 3D organization of cellulose microfibrils in plastic resin-embedded, delignified cell walls of radiata pine early wood. The ∼ 1 nm thick tomographic slices produced in this study provided for a resolution of ∼ 2 nm in the cross-section of the slices throughout the 150 nm thick plastic sections. This resolution is sufficient to resolve individual cellulose microfibrils and to map the 3D organization of the cellulose microfibrils within the S2 layer of the secondary cell walls. The individual cellulose microfibrils measure ∼ 3.2 nm in diameter, and appear to consist of a ∼ 2.2 nm unstained core and a ∼ 0.5 nm thick surface layer that is lightly stained. Both individual and clustered cellulose microfibrils are seen surrounded by more heavily stained and irregularly shaped residual lignin and hemicellulose. The tightness of packing of the cellulose microfibrils in the cluster varies along the thickness of the section. These findings demonstrate that dual-axis electron tomography is a technique that can provide new insights into the 3D organization of cellulose microfibrils in plant cell walls.

Interrelation between Lignin Deposition and Polysaccharide Matrices during the Assembly of Plant Cell Walls

Abstract: The modifications caused by genetic down‐regulation of the enzyme cinnamoyl CoA reductase (CCR) from monolignol biosynthetic pathways on tobacco and Arabidopsis thaliana were investigated at the ultrastructural level. A typical result was that the same transformation led to similar abnormality in secondary wall formation of fibres in both plants. The cell wall alterations mainly consisted in an important disorganization and loosening of cellulose microfibrils in the inner part of the S2 layer. This inability of the transformants to form a coherent cell wall coincided with a lack of synthesis of non‐condensed forms of lignin in this disorganized region of the wall, as demonstrated by immunolabelling of lignin subunits. A similar disorganization was observed during fibre wall formation in the differentiating tissues of young Populus and A. thaliana plants. The transitory lack of organization of cellulose microfibrils, also coincided with a depletion in non‐condensed forms of lignins. These results suggest that such lignin substructures may be involved in the cohesion of secondary walls during cell wall biogenesis. The mutual influence of the cellulose‐hemicellulose environment and monolignol local polymerization is discussed.