Mechanism Of Cell Wall Formation Research Articles

Rice Brittle Culm19 Encoding Cellulose Synthase Subunit CESA4 Causes Dominant Brittle Phenotype But has No Distinct Influence on Growth and Grain Yield

BackgroundMechanical strength is a crucial agronomic trait in rice (Oryza sativa), and brittle mutants are thought suitable materials to investigate the mechanism of cell wall formation. So far, almost all brittle mutants are recessive, and most of them are defected in multiple morphologies and/or grain yield, limiting their application in hybrid breeding and in rice straw recycling.ResultsWe identified a semi-dominant brittle mutant Brittle culm19 (Bc19) isolated from the japonica variety Nipponbare through chemical mutagenesis. The mutant showed the same apparent morphologies and grain yield to the wild type plant except for its weak mechanical strength. Its development of secondary cell wall in sclerenchyma cells was affected, along with reduced contents of cellulose, hemicellulose, lignin and sugars in culms and leaves. Positional cloning suggested that the Bc19 gene was allelic to OsCESA4, encoding one of the cellulose synthase A (CESA) catalytic subunits. In this mutant, a C-to-T substitution occurred in the coding sequence of BC19, causing the P507S missense mutation in its encoded product, which was located in the second cytoplasmic region of the OsCESA4 protein. Furthermore, introducing mutant gene Bc19 into the wild-type plant resulted in brittle plants, confirming that the P507S point mutation in OsCESA4 protein was responsible for the semi-dominant brittle phenotype of Bc19 mutant. Reverse correlation was revealed between cellulose contents and expression levels of mutant gene Bc19 among the homozygous mutant, the hybrid F1 plant, and the Bc19 overexpression transgenic plants, implying that gene Bc19 might affect cellulose synthesis in a dosage-dependent manner.ConclusionsBc19, a semi-dominant brittle mutant allele of gene OsCESA4, was identified using map-based cloning approach. The mutated protein of Bc19 possessing the P507S missense mutation behaved in a dosage-dependent semi-dominant manner. Unique brittle effect on phenotype and semi-dominant genetic quality of gene Bc19 indicated its potential application in grain-straw dual-purpose hybrid rice breeding.

The role of the exocytic pathway in cell wall assembly in yeast.

The cell wall is a dynamic organelle which is tightly controlled for cell morphology, viability, and pathogenesis. It was previously shown that exocytosis is involved in the secretion of some components and enzymes of the cell wall. However, how the secretory pathway affects the cell wall integrity and assembly remains unclear. Here we show that the secretory pathway mutant (sec) cells were sensitive to cell wall antagonists in Saccharomyces cerevisiae, and they were lysed at restrictive conditions but can be rescued by osmotic stabilizers, indicating their cell walls were disrupted. Although glucans were reduced at the cell surface in sec mutants as speculated, the other two main cell wall components, chitins, and mannoproteins, were accumulated at the cell surface. We also found that both the protein level and the phosphorylation level of Slt2 increased in sec mutants. These results suggest that the exocytic pathway has a critical role in cell wall assembly. Our study will help to understand the mechanism of cell wall formation.

Plant Cell Wall Formation and Regulation

Cell wall is one important and characteristic structure of plant cells, which represents the most abundant carbohydrate resources on earth. Based on the development of techniques and knowledge of interdisciplines, much progress has been made in the mechanisms of plant cell wall formation during the past two decades. Basic processes for the synthesis of cell-wall polymers, related vesicle trafficking, transcriptional regulation, and cell wall deposition and remodeling that happen inside and outside cells have been therefore established. In this review, we summarize the hot spot issues and recent progress achieved in the areas of plant cell wall formation and regulation, including new knowledge about cell wall structure and composition, recent findings in the characterization of key components for cellulose biosynthesis at the plasma membrane and for noncellulosic polysaccharide production in the Golgi apparatus, discoveries in the relationship between cytoskeleton and the trafficking processes, and progress in signaling pathways and regulatory network for cell wall formation. All those advances not only further our understanding on the mechanisms of cell wall formation, but also provide the scientific views for exploration and utilization of the economic values of cell wall. In addition, several challenging questions and potential issues regarding this area are discussed.

Xylem development - from the cradle to the grave.

The development and growth of plants, as well as their successful adaptation to a variety of environments, is highly dependent on the conduction of water, nutrients and other important molecules throughout the plant body. Xylem is a specialized vascular tissue that serves as a conduit of water and minerals and provides mechanical support for upright growth. Wood, also known as secondary xylem, constitutes the major part of mature woody stems and roots. In the past two decades, a number of key factors including hormones, signal transducers and (post)transcriptional regulators have been shown to control xylem formation. We outline the main mechanisms shown to be essential for xylem development in various plant species, with an emphasis on Arabidopsis thaliana, as well as several tree species where xylem has a long history of investigation. We also summarize the processes which have been shown to be instrumental during xylem maturation. This includes mechanisms of cell wall formation and cell death which collectively complete xylem cell fate.

Biotechnology of fibrous flax in Europe and China

Flax, being an ancient crop, has performed a significant role throughout human history. The principal use of flax was industrial, manufacturing textiles from fiber and paints and varnishes from oil. However, in the last decades decline in flax cultivation has been observed. Nevertheless, recently the renewed interest in flax products has been noticed. This is due to research findings suggesting that the flax raw material provides a variety of industrial and health benefits. Flax oil is characterized by high content of linolenic acid (ω-3 group) increasingly used as a human diet supplement protecting against atherosclerosis. Flax fiber gains more and more applications, like in the automobile and construction industries as recyclable composite material. Unique flax fibers are equipped, by genetic engineering, with polyhydroxybutyrate (PHB) since they are compatible with synthetic polymers (polypropylene and polystyrene) and facilitate their biodegradability. The PHB-fiber embedded in polylactide may also serve as a scaffold for tissue engineering and has been shown to be useful as biodegradable implant. The soluble and insoluble fibers are becoming increasingly used in human nutrition.According to the experimental data found in the literature, the changes in the gene expression can lead to cell wall structure alterations in various plant species. The modifications aimed at genes from different fibrous species have been based on the knowledge about the mechanism of cell wall formation in model plant species (e.g. Arabidopsis, poplar, tobacco). Considering the genomic data (flax genome sequence) the genes encoding transcription factors that control cell wall polymer biosynthesis are also among the potential targets for genetic manipulations.As biological and genomic information is widely available, researchers can use diverse biotechnological approaches in order to enhance the quality of flax fibers. Fiber structure can be the subject to modifications by employing either conventional or genetic engineering approaches, by manipulating the native polymers or by introducing novel polymeric compounds, as shown in a number of scientific publications. For example, numerous studies have emphasized the role of lignin biosynthesis genes in controlling the secondary cell wall formation. In other studies, it is reported that the stem tissue targeted PHB biosynthesis strongly affects fiber content and mechanical properties. New approach for flax modification with the use of oligonucleotides that remodel targeted gene methylation and thus gene expression and finally plant improvement is reported.The present study summarizes the recent progress in the biotechnology of flax breeding in Europe and China, the two top flax fiber producers. It is concluded that classical breeding methods supported by genetic engineering technology can accelerate the breeding efficiency for improved yield and quality of ‘new’ flax.

Survey of Genes Involved in Rice Secondary Cell Wall Formation Through a Co-Expression Network

The plant secondary cell wall is the major source of lignocellulosic biomass, a renewable energy resource that can be used for bioethanol production. To comprehensively identify transcription factors (TFs), glycosyltransferase (GT) and glycosyl hydrolase (GH) involved in secondary cell wall formation in rice (Oryza sativa), co-expression network analysis was performed using 68 microarray data points for different rice tissues and stages. In addition to rice genes encoding orthologs of Arabidopsis thaliana TFs known to regulate secondary cell wall formation, the network analysis suggested many novel TF genes likely to be involved in cell wall formation. In the accompanying paper (Hirano et al.), several of these TFs are shown to be involved in rice secondary cell wall formation. Based on a comparison of the rice and Arabidopsis networks, TFs were classified as common to both species or specific to each plant species, suggesting that in addition to a common transcriptional regulatory mechanism of cell wall formation, the two plants may also use species-specific groups of TFs during secondary wall formation. Similarly, genes encoding GT and GH were also classified as genes showing species-common or species-specific expression patterns. In addition, genes for primary or secondary cell wall formation were also suggested. The list of rice TF, GT and GH genes provides an opportunity to unveil the regulation of secondary cell wall formation in grasses, leading to optimization of the cell wall for biofuel production.

Populus resequencing: towards genome-wide association studies

Genome-wide association studies (GWAS) have been used to identify regions of the genome related to various phenotypes in humans, corn, rice and cattle. Successful application of this approach to bioenergy crops such as Populus requires 1) an appropriate mapping population, 2) high-quality phenotypic data and 3) informative genotypic data. With the goal of reducing the recalcitrance of lignocellulosic biomass for economic production of biofuels and understanding basic mechanisms of cell wall formation in Populus we established 4 clonally replicated common gardens experiments each with 1100 native P. trichocarpa genotypes collected from along the northwest coast of the U.S. and Canada. A high-throughput phenotyping pipeline was developed to measure cell wall chemistry, pretreatment response and enzymatic sugar release. Initially 18 genotypes were resequenced to an average 30X depth in order to design a SNP array to test for statistical association using MMAX and PCA methods of testing among ca. 2500 candidate genes. Genetic structure and linkage disequilibrium (LD) was assessed using SSR and SNP markers. Outlying genotypes were excluded from the analyses and estimates of LD were used to design the bead array. Candidate genes were selected based on QTL intervals, expression profiling within developing xylem and expert opinion. MMAX and PCA results revealed similar significant associations for all measured phenotypes and several SNPs within the candidate gene set explain a relatively high degree of the phenotypic variance. As a result, resequencing has continued in order to conduct GWAS in Populus; the complete set of 1100 genotypes will be complete in 2012.

Rice Brittleness Mutants: A Way to Open the ‘Black Box’ of Monocot Cell Wall BiosynthesisFree Access

Rice is a model organism for studying the mechanism of cell wall biosynthesis and remolding in Gramineae. Mechanical strength is an important agronomy trait of rice (Oryza sativa L.) plants that affects crop lodging and grain yield. As a prominent physical property of cell walls, mechanical strength reflects upon the structure of different wall polymers and how they interact. Studies on the mechanisms that regulate the mechanical strength therefore consequently results in uncovering the genes functioning in cell wall biosynthesis and remodeling. Our group focuses on the study of isolation of brittle culm (bc) mutants and characterization of their corresponding genes. To date, several bc mutants have been reported. The identified genes have covered several pathways of cell wall biosynthesis, revealing many secrets of monocot cell wall biosynthesis. Here, we review the progress achieved in this research field and also highlight the perspectives in expectancy. All of those lend new insights into mechanisms of cell wall formation and are helpful for harnessing the waste rice straws for biofuel production.

Electron tomographic analysis of post-meiotic cytokinesis during pollen development in Arabidopsis thaliana.

The mechanism of cell wall formation after male meiosis was studied in microsporocytes of Arabidopsis thaliana (L.) Heynh. by means of thin-section and immuno-electron microscopy and dual-axis electron tomography of high-pressure-frozen/freeze-substituted cells. The cellularization of four-nucleate microsporocytes involves a novel type of cell plate, called a post-meiotic-type cell plate. As in the syncytial endosperm, the microsporocyte cell plates assemble in association with mini-phragmoplasts. However, in contrast to the endosperm cell plates, post-meiotic type cell plates arise simultaneously across the entire division plane. Vesicles are transported along mini-phragmoplast microtubules by putative kinesin proteins and, prior to fusion, they become connected together by 24-nm-long linkers that resemble exocyst complexes. These vesicles fuse with each other to form wide tubules and wide tubular networks. In contrast to endosperm cell plates, the wide tubular networks in microsporocytes completely lack callose and do not appear to be constricted by dynamin rings. The most peripheral wide tubular networks begin to fuse with the plasma membrane before the more central cell plate assembly sites become integrated into a coherent cell plate. Fusion with the parental plasma membrane triggers callose synthesis and the wide tubular domains are converted into convoluted sheets. As the peripheral convoluted sheets accumulate callose and arabinogalactan proteins, they are converted into stub-like projections, which grow centripetally, i.e. toward the interior of the syncytium, fusing with the wide tubular networks already assembled in the division plane. We also demonstrate that the ribosome-excluding cell plate assembly matrix is delivered to the mini-phragmoplast with the first vesicles, and encompasses all the linked vesicles and intermediate stages in cell plate formation.

On the Cytochemistry of Cell Wall Formation in Poplar Trees

Abstract: The ultrastructure of cell walls and the mechanisms of cell wall formation are still not fully understood. The objective of our study was therefore to obtain additional fine structural details on the deposition of cell wall components during the differentiation of xylem cells in hybrid aspen (Populus tremula L. ×P. tremuloides Michx.) we used as a model tree. At the electron microscope level, PATAg staining revealed a successive deposition of polysaccharides with increasing distance from the cambium. Staining with potassium permanganate and UV microspectrophotometry showed that the cell walls were lignified, with some delay to the deposition of polysaccharides. Immunogold labelling of three lignin types in developing cell walls varied with progressive deposition of cell wall layers. Condensed lignin subunits were localized in corners of cells adjacent to the cambium prior to S1 formation, whereas non‐condensed lignin subunits became labelled only in later stages ‐ in secondary walls near cell corners and simultaneously with the completion of S1 formation. As S2 polysaccharide deposition progressed, the labelling extended towards the lumen. Labelling of peroxidases revealed their presence in cell corner regions of young xylem cells, still lacking a secondary wall, implying that peroxidases are incorporated into the developing cell wall at early developmental stages. A weak labelling of middle lamella regions and secondary walls could also be seen at later stages. The results are discussed in relation to current knowledge on the succession of polysaccharide and lignin deposition in woody cell walls.

The mechanism of cell wall formation

It is shown that cell walls, which form in response to plastic deformation, can be of either pure grain boundary or dipole character, or a combination of the two. In addition, it is further demonstrated that all such cell wall types are basically dipole in nature, and thus possess essentially he same energy. The detailed geometry of the walls in turn depends upon their deformation history. Es wird gezeigt, das Zellenwande, die sich wahrend der plastischen Deformation ausbilden, entweder reine Korngrenzen sein konnen oder Dipolcharakter haben oder eine Kombination von beiden sein konnen. Es wird weiter gezeigt, das alle diese Zellwandtypen grundsatzlich dipolartig sind und somit im wesentlichen dieselbe Energie besitzen. Die ausfuhrliche Geometrie der Wande hangt von ihrer Deformationsvorgeschichte ab.

Formation of Plant Cell Wall Polysaccharides

The study of plant cell wall formation has led to investigations of polysaccharide biosynthesis in cell-free systems1–8. Those systems which have been studied have certain common properties: they are all particulate enzymes; they are all relatively unstable; and those for which the specificity of the substrate has been determined are known to utilize a single sugar nucleotide2,5,7. Detailed characteristics have been reported in some cases5,8, but there is little information which serves to organize these data into a working hypothesis concerning the mechanism of cell wall formation. This report supports the hypothesis9 that the various polysaccharide-synthesizing enzymes originate from a single type of organelle. Furthermore, sedimentation properties suggest that this organelle is the plasma membrane.

A Possible Mechanism of Cell-Wall Formation

GOLDACRE1 has shown that if a surface film of a lipo-protein on water is compressed, it tends to form folds and ultimately cigar-shaped fibres consisting of a double lipo-protein layer with water inside and outside. It was suggested that such fibres could have been a reaction-space for the original formation of living cells. Danielli2 formed double lipo-protein layers by dropping dense protein solution through an oil layer into a less-dense protein solution. In this case, the film was spherical in shape and included a layer of oil. Sigwart and Nassenstein3have formed spherical shells of water in benzene by ejecting benzene drops from a nozzle preferentially wetted by water.