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Cay M Kielty - One of the best experts on this subject based on the ideXlab platform.
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Fibrillin Microfibrils.
Advances in protein chemistry, 2020Co-Authors: Cay M Kielty, Michael J Sherratt, Andrew Marson, Clair BaldockAbstract:Fibrillin Microfibrils are widely distributed extracellular matrix assemblies that endow elastic and nonelastic connective tissues with long-range elasticity. They direct tropoelastin deposition during elastic fibrillogenesis and form an outer mantle for mature elastic fibers. Microfibril arrays are also abundant in dynamic tissues that do not express elastin, such as the ciliary zonules of the eye. Mutations in fibrillin-1-the principal structural component of Microfibrils-cause Marfan syndrome, a heritable disease with severe aortic, ocular, and skeletal defects. Isolated fibrillin-rich Microfibrils have a complex 56 nm "beads-on-a-string" appearance; the molecular basis of their assembly and elastic properties, and their role in higher-order elastic fiber formation, remain incompletely understood.
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Proteomic analysis of fibrillin‐rich Microfibrils
Proteomics, 2020Co-Authors: Stuart A Cain, C Adrian Shuttleworth, Michael J Sherratt, Amanda Morgan, Stephen G. Ball, Cay M KieltyAbstract:MS has been used to investigate the composition of fibrillin-rich Microfibrils from non-elastic and elastic tissues, and to compare fibrillin-1 tryptic fingerprints derived from whole zonules, Microfibrils and recombinant fibrillin-1. In all microfibril preparations, fibrillin-1 was abundant and the only fibrillin isoform. MAGP-1 was the only other microfibril-associated molecule. gamma-Crystallin co-purified with zonular Microfibrils, so this association may contribute to ciliary zonule anchorage to lens. Recombinant fibrillin-1 tryptic peptides mapped throughout the molecule and included virtually all predicted peptides except for those larger than 4.5 kDa, smaller than 600 Da or post-translationally modified. In contrast, fewer microfibril tryptic fibrillin-1 peptides were detected, although they were derived from domains throughout the molecule and included two peptides after the C-terminal furin processing site. Several microfibril-derived N- and C-terminal domains never yielded any peptides, while tryptic peptides from other domains yielded numerous peptides, suggesting that some tissue microfibril features are retained after trypsinisation. This first MS analysis of a purified extracellular matrix assembly has provided new insights into microfibril composition and fibrillin-1 organisation within them.
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epithelial mesenchymal status influences how cells deposit fibrillin Microfibrils
Journal of Cell Science, 2014Co-Authors: Andrew K Baldwin, Stuart A Cain, Rachel Lennon, Alan R F Godwin, Catherine L R Merry, Cay M KieltyAbstract:Here, we show that epithelial–mesenchymal status influences how cells deposit extracellular matrix. Retinal pigmented epithelial (RPE) cells that expressed high levels of E-cadherin and had cell–cell junctions rich in zona occludens (ZO)-1, β-catenin and heparan sulfate, required syndecan-4 but not fibronectin or protein kinase C α (PKCα) to assemble extracellular matrix (fibrillin Microfibrils and perlecan). In contrast, RPE cells that strongly expressed mesenchymal smooth muscle α-actin but little ZO-1 or E-cadherin, required fibronectin (like fibroblasts) and PKCα, but not syndecan-4. Integrins α5β1 and/or α8β1 and actomyosin tension were common requirements for microfibril deposition, as was heparan sulfate biosynthesis. TGFβ, which stimulates epithelial–mesenchymal transition, altered gene expression and overcame the dependency on syndecan-4 for microfibril deposition in epithelial RPE cells, whereas blocking cadherin interactions disrupted microfibril deposition. Renal podocytes had a transitional phenotype with pericellular β-catenin but little ZO-1; they required syndecan-4 and fibronectin for efficient microfibril deposition. Thus, epithelial–mesenchymal status modulates microfibril deposition.
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assembly of fibrillin Microfibrils governs extracellular deposition of latent tgfβ
Journal of Cell Science, 2010Co-Authors: Teresa Massamwu, Amanda Mcgovern, Shazia S. Chaudhry, Clair Baldock, Adrian C Shuttleworth, Maybo Chiu, Rawshan Choudhury, Andrew K Baldwin, Cay M KieltyAbstract:Control of the bioavailability of the growth factor TGFβ is essential for tissue formation and homeostasis, yet precisely how latent TGFβ is incorporated into the extracellular matrix is unknown. Here, we show that deposition of a large latent TGFβ complex (LLC), which contains latent TGFβ-binding protein 1 (LTBP-1), is directly dependent on the pericellular assembly of fibrillin Microfibrils, which interact with fibronectin during higher-order fibrillogenesis. LTBP-1 formed pericellular arrays that colocalized with Microfibrils, whereas fibrillin knockdown inhibited fibrillar LTBP-1 and/or LLC deposition. Blocking α5β1 integrin or supplementing cultures with heparin, which both inhibited microfibril assembly, disrupted LTBP-1 deposition and enhanced Smad2 phosphorylation. Full-length LTBP-1 bound only weakly to N-terminal pro-fibrillin-1, but this association was strongly enhanced by heparin. The microfibril-associated glycoprotein MAGP-1 (MFAP-2) inhibited LTBP-1 binding to fibrillin-1 and stimulated Smad2 phosphorylation. By contrast, fibulin-4, which interacted strongly with full-length LTBP-1, did not induce Smad2 phosphorylation. Thus, LTBP-1 and/or LLC deposition is dependent on pericellular microfibril assembly and is governed by complex interactions between LTBP-1, heparan sulfate, fibrillin-1 and microfibril-associated molecules. In this way, Microfibrils control TGFβ bioavailability.
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Fibrillin-1 microfibril deposition is dependent on fibronectin assembly.
Journal of cell science, 2008Co-Authors: Rachel Kinsey, Matthew R Williamson, Shazia Chaudhry, Kieran T Mellody, Amanda Mcgovern, Seiichiro Takahashi, C Adrian Shuttleworth, Cay M KieltyAbstract:Newly deposited Microfibrils strongly colocalise with fibronectin in primary fibroblasts. Microfibril formation is grossly inhibited by fibronectin depletion, but rescued by supplementation with exogenous cellular fibronectin. As integrin receptors are key determinants of fibronectin assembly, we investigated whether they also influenced microfibril deposition. Analysis of beta1-integrin-receptor-null fibroblasts, blockage of cell surface integrin receptors that regulate fibronectin assembly and disruption of Rho kinase all result in suppressed deposition of both fibronectin and Microfibrils. Antibody activation of beta1 integrins in fibronectin-depleted cultures is insufficient to rescue microfibril assembly. In fibronectin(RGE/RGE) mutant mouse fibroblast cultures, which do not engage alpha5beta1 integrin, extracellular assembly of both fibronectin and Microfibrils is markedly reduced. Thus, pericellular microfibril assembly is regulated by fibronectin fibrillogenesis.
Michael J Sherratt - One of the best experts on this subject based on the ideXlab platform.
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Fibrillin Microfibrils.
Advances in protein chemistry, 2020Co-Authors: Cay M Kielty, Michael J Sherratt, Andrew Marson, Clair BaldockAbstract:Fibrillin Microfibrils are widely distributed extracellular matrix assemblies that endow elastic and nonelastic connective tissues with long-range elasticity. They direct tropoelastin deposition during elastic fibrillogenesis and form an outer mantle for mature elastic fibers. Microfibril arrays are also abundant in dynamic tissues that do not express elastin, such as the ciliary zonules of the eye. Mutations in fibrillin-1-the principal structural component of Microfibrils-cause Marfan syndrome, a heritable disease with severe aortic, ocular, and skeletal defects. Isolated fibrillin-rich Microfibrils have a complex 56 nm "beads-on-a-string" appearance; the molecular basis of their assembly and elastic properties, and their role in higher-order elastic fiber formation, remain incompletely understood.
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Proteomic analysis of fibrillin‐rich Microfibrils
Proteomics, 2020Co-Authors: Stuart A Cain, C Adrian Shuttleworth, Michael J Sherratt, Amanda Morgan, Stephen G. Ball, Cay M KieltyAbstract:MS has been used to investigate the composition of fibrillin-rich Microfibrils from non-elastic and elastic tissues, and to compare fibrillin-1 tryptic fingerprints derived from whole zonules, Microfibrils and recombinant fibrillin-1. In all microfibril preparations, fibrillin-1 was abundant and the only fibrillin isoform. MAGP-1 was the only other microfibril-associated molecule. gamma-Crystallin co-purified with zonular Microfibrils, so this association may contribute to ciliary zonule anchorage to lens. Recombinant fibrillin-1 tryptic peptides mapped throughout the molecule and included virtually all predicted peptides except for those larger than 4.5 kDa, smaller than 600 Da or post-translationally modified. In contrast, fewer microfibril tryptic fibrillin-1 peptides were detected, although they were derived from domains throughout the molecule and included two peptides after the C-terminal furin processing site. Several microfibril-derived N- and C-terminal domains never yielded any peptides, while tryptic peptides from other domains yielded numerous peptides, suggesting that some tissue microfibril features are retained after trypsinisation. This first MS analysis of a purified extracellular matrix assembly has provided new insights into microfibril composition and fibrillin-1 organisation within them.
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structural and compositional diversity of fibrillin Microfibrils in human tissues
Journal of Biological Chemistry, 2018Co-Authors: Alexander Eckersley, Kieran T Mellody, Clair Baldock, Suzanne M Pilkington, Christopher E M Griffiths, Rachel E B Watson, Ronan Ocualain, David C Knight, Michael J SherrattAbstract:Elastic fibers comprising fibrillin Microfibrils and elastin are present in many tissues, including the skin, lungs, and arteries, where they confer elasticity and resilience. Although fibrillin Microfibrils play distinct and tissue-specific functional roles, it is unclear whether their ultrastructure and composition differ between elastin-rich (skin) and elastin-poor (ciliary body and zonule) organs or after in vitro synthesis by cultured cells. Here, we used atomic force microscopy, which revealed that the bead morphology of fibrillin Microfibrils isolated from the human eye differs from those isolated from the skin. Using newly developed pre-MS preparation methods and LC-MS/MS, we detected tissue-specific regions of the fibrillin-1 primary structure that were differentially susceptible to proteolytic extraction. Comparing tissue- and culture-derived Microfibrils, we found that dermis- and dermal fibroblast–derived fibrillin Microfibrils differ in both bead morphology and periodicity and also exhibit regional differences in fibrillin-1 proteolytic susceptibility. In contrast, collagen VI Microfibrils from the same dermal or fibroblast samples were invariant in ultrastructure (periodicity) and protease susceptibility. Finally, we observed that skin- and eye-derived microfibril suspensions were enriched in elastic fiber– and basement membrane–associated proteins, respectively. LC-MS/MS also identified proteins (such as calreticulin and protein-disulfide isomerase) that are potentially fundamental to fibrillin microfibril biology, regardless of their tissue source. Fibrillin Microfibrils synthesized in cell culture lacked some of these key proteins (MFAP2 and -4 and fibrillin-2). These results showcase the structural diversity of these key extracellular matrix assemblies, which may relate to their distinct roles in the tissues where they reside.
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proteomic analysis of fibrillin rich Microfibrils
Proteomics, 2006Co-Authors: Stuart A Cain, Cay M Kielty, Michael J Sherratt, Adrian C Shuttleworth, Amanda Morgan, Stephen BallAbstract:MS has been used to investigate the composition of fibrillin-rich Microfibrils from non-elastic and elastic tissues, and to compare fibrillin-1 tryptic fingerprints derived from whole zonules, Microfibrils and recombinant fibrillin-1. In all microfibril preparations, fibrillin-1 was abundant and the only fibrillin isoform. MAGP-1 was the only other microfibril-associated molecule. gamma-Crystallin co-purified with zonular Microfibrils, so this association may contribute to ciliary zonule anchorage to lens. Recombinant fibrillin-1 tryptic peptides mapped throughout the molecule and included virtually all predicted peptides except for those larger than 4.5 kDa, smaller than 600 Da or post-translationally modified. In contrast, fewer microfibril tryptic fibrillin-1 peptides were detected, although they were derived from domains throughout the molecule and included two peptides after the C-terminal furin processing site. Several microfibril-derived N- and C-terminal domains never yielded any peptides, while tryptic peptides from other domains yielded numerous peptides, suggesting that some tissue microfibril features are retained after trypsinisation. This first MS analysis of a purified extracellular matrix assembly has provided new insights into microfibril composition and fibrillin-1 organisation within them.
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fibulin 5 interacts with fibrillin 1 molecules and Microfibrils
Biochemical Journal, 2005Co-Authors: Lyle J Freeman, Kieran T Mellody, Michael J Sherratt, Amanda Lomas, Nigel Hodson, Anthony S Weiss, Adrian Shuttleworth, Cay M KieltyAbstract:Fibulin-5 plays an important role in elastic fibre formation in vivo. We have investigated the molecular interactions between fibulin-5 and components of fibrillin-rich Microfibrils which form a template for elastin. Fibulin-5 interacted in a dose-dependent manner with a fibrillin-1 N-terminal sequence and with tropoelastin, but not with MAGP-1 (microfibril-associated glycoprotein-1) or decorin. Fibulin-5 did not inhibit interactions between fibrillin-1 N- and C-terminal fragments, or fibrillin-1 interactions with tropoelastin. Fibulin-5 may provide a link between tropoelastin and Microfibrils in the pericellular space during elastic fibre assembly.
Tobias I. Baskin - One of the best experts on this subject based on the ideXlab platform.
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cell wall extension results in the coordinate separation of parallel Microfibrils evidence from scanning electron microscopy and atomic force microscopy
Plant Journal, 2005Co-Authors: Francoise Marga, Daniel J Cosgrove, Michel Grandbois, Tobias I. BaskinAbstract:*† ‡ § Summary Enlargement of the cell wall requires separation of cellulose Microfibrils, mediated by proteins such as expansin; according to the multi-net growth hypothesis, enlargement passively reorients Microfibrils. However, at the molecular scale, little is known about the specific movement of Microfibrils. To find out, we examined directly changes in microfibril orientation when walls were extended slowly in vitro under constant load (creep). Frozen-thawed cucumber hypocotyl segments were strained by 20‐30% by incubation in pH 4.5 buffer or by incubation of heat-inactivated segments in a-expansin or a fungal endoglucanase (Cel12A). Subsequently, the innermost layer of the cell wall was imaged, with neither extraction nor homogenization, by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). AFM images revealed that sample preparation for FESEM did not appreciably alter cell wall ultrastructure. In both FESEM and AFM, images from extended and non-extended samples appeared indistinguishable. To quantify orientational order, we used a novel algorithm to characterize the fast Fourier transform of the image as a function of spatial frequency. For both FESEM and AFM images, the transforms of non-extended samples were indistinguishable from those of samples extended by a-expansin or Cel12A, as were AFM images of samples extended by acidic buffer. We conclude that cell walls in vitro can extend slowly by a creep mechanism without passive reorientation of innermost Microfibrils, implying that wall loosening agents act selectively on the cross-linking polymers between parallel Microfibrils, rather than more generally on the wall matrix.
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ANISOTROPIC EXPANSION OF THE PLANT CELL WALL
Annual Review of Cell and Developmental Biology, 2005Co-Authors: Tobias I. BaskinAbstract:Plants shape their organs with a precision demanded by optimal function; organ shaping requires control over cell wall expansion anisotropy. Focusing on multicellular organs, I survey the occurrence of expansion anisotropy and discuss its causes and proposed controls. Expansion anisotropy of a unit area of cell wall is characterized by the direction and degree of anisotropy. The direction of maximal expansion rate is usually regulated by the direction of net alignment among cellulose Microfibrils, which overcomes the prevailing stress anisotropy. In some stems, the directionality of expansion of epidermal cells is controlled by that of the inner tissue. The degree of anisotropy can vary widely as a function of position and of treatment. The degree of anisotropy is probably controlled by factors in addition to the direction of microfibril alignment. I hypothesize that rates of expansion in maximal and minimal directions are regulated by distinct molecular mechanisms that regulate interactions between matrix and Microfibrils.
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on the alignment of cellulose Microfibrils by cortical microtubules a review and a model
Protoplasma, 2001Co-Authors: Tobias I. BaskinAbstract:The hypothesis that microtubules align Microfibrils, termed the alignment hypothesis, states that there is a causal link between the orientation of cortical microtubules and the orientation of nascent Microfibrils. I have assessed the generality of this hypothesis by reviewing what is known about the relation between microtubules and Microfibrils in a wide group of examples: in algae of the family Characeae,Closterium acerosum, Oocystis solitaria, and certain genera of green coenocytes and in land plant tip-growing cells, xylem, diffusely growing cells, and protoplasts. The salient features about microfibril alignment to emerge are as follows. Cellulose Microfibrils can be aligned by cortical microtubules, thus supporting the alignment hypothesis. Alignment of Microfibrils can occur independently of microtubules, showing that an alternative to the alignment hypothesis must exist. Microfibril organization is often random, suggesting that self-assembly is insufficient. Microfibril organization differs on different faces of the same cell, suggesting that Microfibrils are aligned locally, not with respect to the entire cell. Nascent Microfibrils appear to associate tightly with the plasma membrane. To account for these observations, I present a model that posits alignment to be mediated through binding the nascent microfibril. The model, termed templated incorporation, postulates that the nascent microfibril is incorporated into the cell wall by binding to a scaffold that is oriented; further, the scaffold is built and oriented around either already incorporated Microfibrils or plasma membrane proteins, or both. The role of cortical microtubules is to bind and orient components of the scaffold at the plasma membrane. In this way, spatial information to align the Microfibrils may come from either the cell wall or the cell interior, and microfibril alignment with and without microtubules are subsets of a single mechanism.
Daniel J Cosgrove - One of the best experts on this subject based on the ideXlab platform.
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the shape of native plant cellulose Microfibrils
Scientific Reports, 2018Co-Authors: James D. Kubicki, Daniel P. Oehme, Hui Yang, Daisuke Sawada, Hugh Oneill, Daniel J CosgroveAbstract:Determining the shape of plant cellulose Microfibrils is critical for understanding plant cell wall molecular architecture and conversion of cellulose into biofuels. Only recently has it been determined that these cellulose Microfibrils are composed of 18 cellulose chains rather than 36 polymers arranged in a diamond-shaped pattern. This study uses density functional theory calculations to model three possible habits for the 18-chain microfibril and compares the calculated energies, structures, 13C NMR chemical shifts and WAXS diffractograms of each to evaluate which shape is most probable. Each model is capable of reproducing experimentally-observed data to some extent, but based on relative theoretical energies and reasonable reproduction of all variables considered, a microfibril based on 5 layers in a 34443 arrangement is predicted to be the most probable. A habit based on a 234432 arrangement is slightly less favored, and a 6 × 3 arrangement is considered improbable.
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nanoscale movements of cellulose Microfibrils in primary cell walls
Nature plants, 2017Co-Authors: Tian Zhang, Dimitrios Vavylonis, Daniel M Durachko, Daniel J CosgroveAbstract:The growing plant cell wall is commonly considered to be a fibre-reinforced structure whose strength, extensibility and anisotropy depend on the orientation of crystalline cellulose Microfibrils, their bonding to the polysaccharide matrix and matrix viscoelasticity1–4. Structural reinforcement of the wall by stiff cellulose Microfibrils is central to contemporary models of plant growth, mechanics and meristem dynamics4–12. Although passive microfibril reorientation during wall extension has been inferred from theory and from bulk measurements13–15, nanometre-scale movements of individual Microfibrils have not been directly observed. Here we combined nanometre-scale imaging of wet cell walls by atomic force microscopy (AFM) with a stretching device and endoglucanase treatment that induces wall stress relaxation and creep, mimicking wall behaviours during cell growth. Microfibril movements during forced mechanical extensions differ from those during creep of the enzymatically loosened wall. In addition to passive angular reorientation, we observed a diverse repertoire of microfibril movements that reveal the spatial scale of molecular connections between Microfibrils. Our results show that wall loosening alters microfibril connectivity, enabling microfibril dynamics not seen during mechanical stretch. These insights into microfibril movements and connectivities need to be incorporated into refined models of plant cell wall structure, growth and morphogenesis. Plant cell growth requires cell wall extension. Here, the nanoscale movement of cellulose Microfibrils in onion primary cell wall is imaged by atomic force microscopy and compared under mechanical extension versus enzymatic loosening.
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spatial organization of cellulose Microfibrils and matrix polysaccharides in primary plant cell walls as imaged by multichannel atomic force microscopy
Plant Journal, 2016Co-Authors: Tian Zhang, Yunzhen Zheng, Daniel J CosgroveAbstract:Summary We used atomic force microscopy (AFM), complemented with electron microscopy, to characterize the nanoscale and mesoscale structure of the outer (periclinal) cell wall of onion scale epidermis – a model system for relating wall structure to cell wall mechanics. The epidermal wall contains ~100 lamellae, each ~40 nm thick, containing 3.5-nm wide cellulose Microfibrils oriented in a common direction within a lamella but varying by ~30 to 90° between adjacent lamellae. The wall thus has a crossed polylamellate, not helicoidal, wall structure. Montages of high-resolution AFM images of the newly deposited wall surface showed that single Microfibrils merge into and out of short regions of microfibril bundles, thereby forming a reticulated network. Microfibril direction within a lamella did not change gradually or abruptly across the whole face of the cell, indicating continuity of the lamella across the outer wall. A layer of pectin at the wall surface obscured the underlying cellulose Microfibrils when imaged by FESEM, but not by AFM. The AFM thus preferentially detects cellulose Microfibrils by probing through the soft matrix in these hydrated walls. AFM-based nanomechanical maps revealed significant heterogeneity in cell wall stiffness and adhesiveness at the nm scale. By color coding and merging these maps, the spatial distribution of soft and rigid matrix polymers could be visualized in the context of the stiffer Microfibrils. Without chemical extraction and dehydration, our results provide multiscale structural details of the primary cell wall in its near-native state, with implications for Microfibrils motions in different lamellae during uniaxial and biaxial extensions.
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cell wall extension results in the coordinate separation of parallel Microfibrils evidence from scanning electron microscopy and atomic force microscopy
Plant Journal, 2005Co-Authors: Francoise Marga, Daniel J Cosgrove, Michel Grandbois, Tobias I. BaskinAbstract:*† ‡ § Summary Enlargement of the cell wall requires separation of cellulose Microfibrils, mediated by proteins such as expansin; according to the multi-net growth hypothesis, enlargement passively reorients Microfibrils. However, at the molecular scale, little is known about the specific movement of Microfibrils. To find out, we examined directly changes in microfibril orientation when walls were extended slowly in vitro under constant load (creep). Frozen-thawed cucumber hypocotyl segments were strained by 20‐30% by incubation in pH 4.5 buffer or by incubation of heat-inactivated segments in a-expansin or a fungal endoglucanase (Cel12A). Subsequently, the innermost layer of the cell wall was imaged, with neither extraction nor homogenization, by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). AFM images revealed that sample preparation for FESEM did not appreciably alter cell wall ultrastructure. In both FESEM and AFM, images from extended and non-extended samples appeared indistinguishable. To quantify orientational order, we used a novel algorithm to characterize the fast Fourier transform of the image as a function of spatial frequency. For both FESEM and AFM images, the transforms of non-extended samples were indistinguishable from those of samples extended by a-expansin or Cel12A, as were AFM images of samples extended by acidic buffer. We conclude that cell walls in vitro can extend slowly by a creep mechanism without passive reorientation of innermost Microfibrils, implying that wall loosening agents act selectively on the cross-linking polymers between parallel Microfibrils, rather than more generally on the wall matrix.
Zheng-hua Ye - One of the best experts on this subject based on the ideXlab platform.
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alteration of oriented deposition of cellulose Microfibrils by mutation of a katanin like microtubule severing protein
The Plant Cell, 2002Co-Authors: David H. Burk, Zheng-hua YeAbstract:It has long been hypothesized that cortical microtubules (MTs) control the orientation of cellulose microfibril deposition, but no mutants with alterations of MT orientation have been shown to affect this process. We have shown previously that in Arabidopsis, the fra2 mutation causes aberrant cortical MT orientation and reduced cell elongation, and the gene responsible for the fra2 mutation encodes a katanin-like protein. In this study, using field emission scanning electron microscopy, we found that the fra2 mutation altered the normal orientation of cellulose Microfibrils in walls of expanding cells. Although cellulose Microfibrils in walls of wild-type cells were oriented transversely along the elongation axis, cellulose Microfibrils in walls of fra2 cells often formed bands and ran in different directions. The fra2 mutation also caused aberrant deposition of cellulose Microfibrils in secondary walls of fiber cells. The aberrant orientation of cellulose Microfibrils was shown to be correlated with disorganized cortical MTs in several cell types examined. In addition, the thickness of both primary and secondary cell walls was reduced significantly in the fra2 mutant. These results indicate that the katanin-like protein is essential for oriented cellulose microfibril deposition and normal cell wall biosynthesis. We further demonstrated that the Arabidopsis katanin-like protein possessed MT-severing activity in vitro; thus, it is an ortholog of animal katanin. We propose that the aberrant MT orientation caused by the mutation of katanin results in the distorted deposition of cellulose Microfibrils, which in turn leads to a defect in cell elongation. These findings strongly support the hypothesis that cortical MTs regulate the oriented deposition of cellulose Microfibrils that determines the direction of cell elongation.
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A Kinesin-Like Protein Is Essential for Oriented Deposition of Cellulose Microfibrils and Cell Wall Strength
The Plant Cell, 2002Co-Authors: Ruiqin Zhong, David H. Burk, W. Herbert Morrison, Zheng-hua YeAbstract:Cortical microtubules have long been hypothesized to regulate the oriented deposition of cellulose Microfibrils. However, the molecular mechanisms of how microtubules direct the orientation of cellulose microfibril deposition are not known. We have used fibers in the inflorescence stems of Arabidopsis to study secondary wall deposition and cell wall strength and found a fragile fiber (fra1) mutant with a dramatic reduction in the mechanical strength of fibers. The fra1 mutation did not cause any defects in cell wall composition, secondary wall thickening, or cortical microtubule organization in fiber cells. An apparent alteration was found in the orientation of cellulose Microfibrils in fra1 fiber walls, indicating that the reduced mechanical strength of fra1 fibers probably was attributable to altered cellulose microfibril deposition. The FRA1 gene was cloned and found to encode a kinesin-like protein with an N-terminal microtubule binding motor domain. The FRA1 protein was shown to be concentrated around the periphery of the cytoplasm but absent in the nucleus. Based on these findings, we propose that the FRA1 kinesin-like protein is involved in the microtubule control of cellulose microfibril order.