Plant Cell Wall Synthesis Research Articles

Molecular analysis of 10 coding regions from Arabidopsis that are homologous to the MUR3 xyloglucan galactosyltransferase.

Plant cell walls are composed of a large number of complex polysaccharides, which contain at least 13 different monosaccharides in a multitude of linkages. This structural complexity of cell wall components is paralleled by a large number of predicted glycosyltransferases in plant genomes, which can be grouped into several distinct families based on conserved sequence motifs (B. Henrissat, G.J. Davies [2000] Plant Physiol 124: 1515-1519). Despite the wealth of genomic information in Arabidopsis and several crop plants, the biochemical functions of these coding regions have only been established in a few cases. To lay the foundation for the genetic and biochemical characterization of putative glycosyltransferase genes, we conducted a phylogenetic and expression analysis on 10 predicted coding regions (AtGT11-20) that are closely related to the MUR3 xyloglucan galactosyltransferase of Arabidopsis. All of these proteins contain the conserved sequence motif pfam 03016 that is the hallmark of the beta-d-glucuronosyltransferase domain of exostosins, a class of animal enzymes involved in the biosynthesis of the extracellular polysaccharide heparan sulfate. Reverse transcriptase-polymerase chain reaction and promoter:beta-glucuronidase studies indicate that all AtGT genes are transcribed. Although six of the 10 AtGT genes were expressed in all major plant organs, the remaining four genes showed more restricted expression patterns that were either confined to specific organs or to highly specialized cell types such as hydathodes or pollen grains. T-DNA insertion mutants in AtGT13 and AtGT18 displayed reductions in the Gal content of total cell wall material, suggesting that the disrupted genes encode galactosyltransferases in plant cell wall synthesis.

The Cell Walls that Bind the Tree of Life

Abstract Cell walls have evolved independently in many phyletically diverse clades, including the Eubacteria and Archaebacteria. However, a review of the available genetic and biochemical evidence indicates that the machinery responsible for synthesizing the cell walls of land plants, of their nearest algal relatives (the charophytes), and of some very ancient algal lineages (chlorophytes, rhodophytes, and phaeophytes) can be traced back to ancient primary endosymbiotic events involving Eubacteria (specifically cyanobacteria and proteobacteria). Lateral gene transfers attending secondary endosymbiotic events appear to be responsible for manufacturing the cell walls of more recently evolved photoautotrophic and heterotrophic lineages (e.g., euglenoids and tunicates). Recent research into the genetic basis of cell wall synthesis and chemical composition in bacteria, algae, and land plants continues to shed light on the phylogenetic relationships among a broad spectrum of evolutionarily and ecologically dive...

Mutation of a family 8 glycosyltransferase gene alters cell wall carbohydrate composition and causes a humidity-sensitive semi-sterile dwarf phenotype in Arabidopsis.

The genome of Arabidopsis thaliana contains about 400 genes coding for glycosyltransferases, many of which are predicted to be involved in the synthesis and remodelling of cell wall components. We describe the isolation of a transposon-tagged mutant, parvus, which under low humidity conditions exhibits a severely dwarfed growth phenotype and failure of anther dehiscence resulting in semi-sterility. All aspects of the mutant phenotype were partially rescued by growth under high-humidity conditions, but not by the application of growth hormones or jasmonic acid. The mutation is caused by insertion of a maize Dissociation (Ds) element in a gene coding for a putative Golgi-localized glycosyltransferase belonging to family 8. Members of this family, originally identified on the basis of similarity to bacterial lipooligosaccharide glycosyltransferases, include enzymes known to be involved in the synthesis of bacterial and plant cell walls. Cell-wall carbohydrate analyses of the parvus mutant indicated reduced levels of rhamnogalacturonan I branching and alterations in the abundance of some xyloglucan linkages that may, however, be indirect consequences of the mutation.

Recombinant UDP-glucose dehydrogenase from soybean

The enzyme UDP-glucose dehydrogenase (UDP-GlcDH, EC 1.1.1.22) converts the nucleotide sugar UDP-glucose (UDP-Glc) into UDP-glucuronic acid (UDP-GlcA), precursor for many sugars in pectins, xyloglucans or arabinose-containing polymers. We have developed a method to produce high amounts of soluble recombinant UDP-GlcDH. The analysis of the substrate specificity indicates that only UDP-Glc but not UDP-galactose is converted into the corresponding uronic acid by the UDP-GlcDH. The K m value for UDP-Glc was calculated to 22 and 70 μM for NAD +, respectively. The soybean ( Glycine max (L.) Merrill) enzyme is inhibited in a competitive manner by UDP-xylose with a K i value of 10 μM, suggesting a feedback control of the production of sugar nucleotides used for the synthesis of plant cell walls. In contrast to the UDP-GlcDH from bovine, which is only active as a hexameric complex, the soybean enzyme catalyses the reaction as a monomer.

Mutations of the secondary cell wall.

It has not been possible to isolate a number of crucial enzymes involved in plant cell wall synthesis. Recent progress in identifying some of these steps has been overcome by the isolation of mutants defective in various aspects of cell wall synthesis and the use of these mutants to identify the corresponding genes. Secondary cell walls offer numerous advantages for genetic analysis of plant cell walls. It is possible to recover very severe mutants since the plants remain viable. In addition, although variation in secondary cell wall composition occurs between different species and between different cell types, the composition of the walls is relatively simple compared to primary cell walls. Despite these advantages, relatively few secondary cell wall mutations have been described to date. The only secondary cell wall mutations characterised to date, in which the basis of the abnormality is known, have defects in either the control of secondary cell wall deposition or secondary cell wall cellulose or lignin biosynthesis. These mutants have, however, provided essential information on secondary cell wall biosynthesis.

A reversibly glycosylated polypeptide (RGP1) possibly involved in plant cell wall synthesis: purification, gene cloning, and trans-Golgi localization.

We purified from pea (Pisum sativum) tissue an approximately 40 kDa reversibly glycosylated polypeptide (RGP1) that can be glycosylated by UDP-Glc, UDP-Xyl, or UDP-Gal, and isolated a cDNA encoding it, apparently derived from a single-copy gene (Rgp1). Its predicted translation product has 364 aminoacyl residues and molecular mass of 41.5 kDa. RGP1 appears to be a membrane-peripheral protein. Immunogold labeling localizes it specifically to trans-Golgi dictyosomal cisternae. Along with other evidence, this suggests that RGP1 is involved in synthesis of xyloglucan and possibly other hemicelluloses. Corn (Zea mays) contains a biochemically similar and structurally homologous RGP1, which has been thought (it now seems mistakenly) to function in starch synthesis. The expressed sequence database also reveals close homologs of pea Rgp1 in Arabidopsis and rice (Oryza sativa). Rice possesses, in addition, a distinct but homologous sequence (Rgp2). RGP1 provides a polypeptide marker for Golgi membranes that should be useful in plant membrane studies.

A unified hypothesis for the role of membrane bound enzyme complexes and microtubules in plant cell wall synthesis

In an attempt to provide a unified hypothesis to account for the various aspects of oriented cellulose fibril synthesis it is proposed that plasmalemma located cellulose synthetase enzyme complexes are free to move in the plane of the membrane. Their directed movement may be produced by a component which is associated with the synthetase complex and which also interacts with cytoplasmic microtubules to generate a sliding force which moves the entire complex through the membrane utilizing the microtubule as a rigid guiding track and thus laying down, in the wake of the complex, cellulose fibrils whose orientation mirrors that of the microtubules.

A new intermediate in plant cell wall synthesis

The synthesis of a soluble uridylic acid containing polysaccharide and of the insoluble pollen tube wall have been studied. The time course of incorporation of arabinose into the soluble and wall fractions and the disappearance of label from arabinose in the soluble fraction and its corresponding increase in the pollen tube wall in pulse-chase experiments, suggest that the soluble polysaccharide is a large precursor subunit of some component of the cell wall.