Cell Walls Of Higher Plants Research Articles

Real-time PCR for quantification in soil of glycoside hydrolase family 6 cellulase genes.

Cellulose is the main structural component of the cell walls of higher plants, representing c. 35-50% of a plant's dry weight; after decomposition and transformation, and constituting a large part of soil organic matter. Telluric micro-organisms able to use cellulose as carbon and energy sources for growth are widely distributed in the environment, but the factors controlling the rate of cellulose degradation are not well understood. In this study, we have developed a quantitative real-time PCR (qPCR) primer set to quantify the glycoside hydrolase family 6 (GH6 family) cellulase genes in soil samples. The qPCR assays were linear over 8 orders of magnitude and sensitive down to 10 copies per assay. qPCR analysis of contrasted soil samples showed densities between 2·47×10(7) and 1·48×10(10) copies per gram of soil. Cloning and sequencing of the PCR products from environmental DNA confirmed both specific amplification (more than 96%) and the wide diversity targeted by the primer set, throughout nearly all the GH6 family, including sequences of bacteria and fungi. Telluric micro-organisms able to use cellulose as carbon and energy sources for growth are widely distributed in the environment, but the factors controlling the rate of cellulose degradation are not well understood. The objective of our study was to develop a qPCR for rapid quantification of GH6 cellulase genes in soil. This qPCR could be applied to study the potential for cellulose degradation in different soils in order to better understand the factors controlling the stability of the soil organic matter.

Health-promoting properties of pectin

Pectin, a heteropolysaccharide commercially derived from the cell wall of higher plants, is mainly used in food as a gelling agent in jams and jellies as well as a stabilizer in fruit juice and milk drinks. It has also received great interest as a source of dietary fiber. Furthermore, pectin is proved to have diverse biological activities including lipid and cholesterol level lowering effects, serum glucose and insulin content lowering effects, gastric emptying delay, and anti-cancer activities. Pectin and pectic oligosaccharides have been shown to induce apoptosis in human colonic adenocarcinoma cells and to have anti-metastatic properties. Dietary pectin can bind metal ions, particularly lead ions, thus reducing their retention in the body and diminishing their toxic effects. On the other hand, pectin enhances intestinal solubility and absorption of ferric iron. Pectin with a low degree of esterification or having a large volume of linear oligogalacturonide segments shows significant mucoadhesion capacity in the gastrointestinal tract. In this way pectin forms a physical barrier protecting epithelium against opportunistic microbial invasion during stress.

Size, shape, and arrangement of native cellulose fibrils in maize cell walls

Higher plant cell walls are the major source of the cellulose used in a variety of industries. Cellulose in plant forms nanoscale fibrils that are embedded in non-cellulosic matrix polymers in the cell walls. The morphological features of plant cellulose fibrils such as the size, shape, and arrangement, are still poorly understood due to its inhomogeneous nature and the limited resolution of the characterization techniques used. Here, we sketch out a proposed model of plant cellulose fibril and its arrangement that is based primarily on review of direct visualizations of different types of cell walls in maize using atomic force microscopy at sub-nanometer scale, and is also inspired by recent advances in understanding of cellulose biosynthesis and biodegradation. We propose that the principal unit of plant cellulose fibril is a 36-chain cellulose elementary fibril (CEF), which is hexagonally shaped and 3.2 × 5.3 nm in cross-section. Macrofibrils are ribbon-like bundles containing variable numbers of CEFs associated through their hydrophilic faces. As the cell expands and/or elongates, large macrofibril may split to become smaller bundles or individual CEFs, which are simultaneously coated with hemicelluloses to form microfibrils of variable sizes during biosynthesis. The microfibrils that contain one CEF are arranged nearly parallel, and the hydrophobic faces of the CEF are perpendicular to the cell wall surface. Structural disordering of the CEF may occur during plant development while cells expand, elongate, dehydrate, and die, as well as during the processing to prepare cellulose materials.

Spatial structure of plant cell wall polysaccharides and its functional significance

Plant polysaccharides comprise the major portion of organic matter in the biosphere. The cell wall built on the basis of polysaccharides is the key feature of a plant organism largely determining its biology. All together, around 10 types of polysaccharide backbones, which can be decorated by different substituents giving rise to endless diversity of carbohydrate structures, are present in cell walls of higher plants. Each of the numerous cell types present in plants has cell wall with specific parameters, the features of which mostly arise from the structure of polymeric components. The structure of polysaccharides is not directly encoded by the genome and has variability in many parameters (molecular weight, length, and location of side chains, presence of modifying groups, etc.). The extent of such variability is limited by the "functional fitting" of the polymer, which is largely based on spatial organization of the polysaccharide and its ability to form supramolecular complexes of an appropriate type. Consequently, the carrier of the functional specificity is not the certain molecular structure but the certain type of the molecules having a certain degree of heterogeneity. This review summarizes the data on structural features of plant cell wall polysaccharides, considers formation of supramolecular complexes, gives examples of tissue- and stage-specific polysaccharides and functionally significant carbohydrate-carbohydrate interactions in plant cell wall, and presents approaches to analyze the spatial structure of polysaccharides and their complexes.

Pectin shows antibacterial activity against <i>Helicobacter pylori</i>

Pectins are the collective name for a group of heterogeneous, high molecular weight, branched polysaccharides that are found in the cell walls of higher plants. In this study, we intend to determine the antibacterial activity of pectin against reference strains and clinical isolates of Helicobacter pylori. The results show that pectin produced antibacterial effects on all the 16 clinical isolates and 2 reference strains of H. pylori with the greatest antibacterial effect at a low pH (5.0) versus higher pHs. The lowest Minimum Inhibitory Concentration recorded was of 0.016 μg/μl. Antibiotic resistance, therapy costs, and undesirable side effects stress the need for new antimicrobials or alternative therapies. The results from our study can further our goal of future eradication of H. pylori infection using new molecules.

Pectin–Cellulose Interactions in the Arabidopsis Primary Cell Wall from Two-Dimensional Magic-Angle-Spinning Solid-State Nuclear Magnetic Resonance

The primary cell wall of higher plants consists of a mixture of polysaccharides whose spatial proximities and interactions with each other are not well understood. We recently obtained the first two-dimensional (2D) and three-dimensional high-resolution magic-angle-spinning (13)C solid-state nuclear magnetic resonance spectra of the uniformly (13)C-labeled primary cell wall of Arabidopsis thaliana, which allowed us to assign the majority of (13)C resonances of the three major classes of polysaccharides: cellulose, hemicellulose, and pectins. In this work, we measured the intensity buildup of (13)C-(13)C cross-peaks in a series of 2D (13)C correlation spectra to obtain semiquantitative information about the spatial proximities between different polysaccharides. Comparison of 2D spectra measured at different spin diffusion mixing times identified intermolecular pectin-cellulose cross-peaks as well as interior cellulose-surface cellulose cross-peaks. The intensity buildup time constants are only modestly longer for cellulose-pectin cross-peaks than for interior cellulose-surface cellulose cross-peaks, indicating that pectins come into direct contact with the cellulose microfibrils. Approximately 25-50% of the cellulose chains exhibit close contact with pectins. The (13)C magnetization of the wall polysaccharides is not fully equilibrated by 1.5 s, indicating that pectins and cellulose are not homogeneously mixed on the molecular level. We also assigned the (13)C signals of cell wall proteins, identifying common residues such as Pro, Hyp, Tyr, and Ala. The chemical shifts indicate significant coil and sheet conformations in these structural proteins. Interestingly, few cross- peaks were observed between the proteins and the polysaccharides. Taken together, these data indicate that the three major types of polysaccharides in the primary wall of Arabidopsis form a single cohesive network, while structural proteins form a relatively separate domain.

Effects of feeding fiber-fermenting bacteria to pigs on nutrient digestion, fecal output, and plasma energy metabolites1,2

Inclusion of feedstuffs with higher plant cell wall (fiber) content in swine diets has increased in recent years due to greater availability and lower cost, especially coproduct feeds, such as corn distillers dried grains with soluble (DDGS). Limitations of feeding higher fiber diets include increased fecal output, which can exceed manure storage volumes, and decreased energy density, which can decrease growth performance; dietary treatments that ameliorate these limitations would benefit pork producers. Grower pigs (n = 48; 61.1 kg initial BW) were used to establish the effects of supplementation of fiber-fermenting bacteria in a 2 × 4 factorial, consisting of 2 diets (standard and high fiber) and 4 bacterial treatments (A, no bacteria; and B, C, and D bacterial supplements). Increased fiber came from inclusion of soybean hulls (10%) and corn DDGS (20%) in the diet. The 3 bacterial supplements (all Bacteroides strains) were isolated from fecal enrichment cultures and selected for their fiber-fermenting capacity. The high fiber diet increased fecal output, blood cholesterol, and triglyceride concentrations, and digestibility of NDF, ADF, and S; CP digestibility decreased (P ≤ 0.10). The improved fiber digestibility and altered energy status of pigs fed the high fiber diet was primarily due to fermentation of soybean hulls, resulting in increased short-chain fatty acid production and absorption, and decreased dietary starch content. Overall, pigs fed the bacterial treatments had only increased blood cholesterol concentrations (P = 0.10). When individual bacterial treatments were compared, pigs fed Bacteria B had decreased fecal output (P ≤ 0.10) and both blood glucose and cholesterol concentrations were increased (P ≤ 0.10) compared with the other 3 treatments, indicating an improved energy status. Pigs fed Bacteria B increased both CP and ADF (P ≤ 0.10), and tended (P = 0.16) to have increased NDF digestibilities compared with pigs fed no bacteria (Treatment A), whereas pigs fed the other 2 bacterial treatments did not differ from pigs fed Bacteria B for nutrient digestibility. Both had similar fecal outputs to pigs fed no bacteria. This is the first report of reduction in fecal output and increased fiber digestibility with pigs fed live bacteria. Successful application of this bacterial treatment could result in improved pig performance and decreased manure volumes, both of which would improve profitability of producers.

Nano- and microstructures in stretched and non-stretched blend gels of cellulose and hemicelluloses

Abstract Molecular interactions between cellulose and hemicelluloses, such as xyloglucan and xylan, play an important role in the formation of ordered layers in the cell wall of higher plants. This study attempts to characterize an ordered state of a matrix consisting of cellulose and hemicellulose induced by stretching never-dried binary blended films. In non-stretched films, the xylan component easily adapted into the semicrystalline state, while the xyloglucan component remained amorphous. Once both blended films were stretched, each component tended to be close enough to the adherent macromolecule, and the interaction resulted in typical morphological orders at the nano- and microscale levels. These studies could be useful in constructing new bio-derived materials, as well as understanding the molecular interactions between the polymers.

Crystalline and amorphous cellulose in the secondary walls of Arabidopsis

In the cell walls of higher plants, cellulose chains are present in crystalline microfibril, with an amorphous part at the surface, or present as amorphous material. To assess the distribution and relative occurrence of the two forms of cellulose in the inflorescence stem of Arabidopsis, we used two carbohydrate-binding modules, CBM3a and CBM28, specific for crystalline and amorphous cellulose, respectively, with immunogold detection in TEM. The binding of the two CBMs displayed specific patterns suggesting that the synthesis of cellulose leads to variable nanodomains of cellulose structures according to cell type. In developing cell walls, only CBM3a bound significantly to the incipient primary walls, indicating that at the onset of its deposition cellulose is in a crystalline structure. As the secondary wall develops, the labeling with both CBMs becomes more intense. The variation of the labeling pattern by CBM3a between transverse and longitudinal sections appeared related to microfibril orientation and differed between fibers and vessels. Although the two CBMs do not allow the description of the complete status of cellulose microstructures, they revealed the dynamics of the deposition of crystalline and amorphous forms of cellulose during wall formation and between cell types adapting cellulose microstructures to the cell function.

Acetylesterase-mediated deacetylation of pectin impairs cell elongation, pollen germination, and plant reproduction.

Pectin is a major component of the primary cell wall of higher plants. Some galacturonyl residues in the backbone of pectinaceous polysaccharides are often O-acetylated at the C-2 or C-3 position, and the resulting acetylesters change dynamically during the growth and development of plants. The processes involve both enzymatic acetylation and deacetylation. Through genomic sequence analysis, we identified a pectin acetylesterase (PAE1) from black cottonwood (Populus trichocarpa). Recombinant Pt PAE1 exhibited preferential activity in releasing the acetate moiety from sugar beet (Beta vulgaris) and potato (Solanum tuberosum) pectin in vitro. Overexpressing Pt PAE1 in tobacco (Nicotiana tabacum) decreased the level of acetyl esters of pectin but not of xylan. Deacetylation engendered differential changes in the composition and/or structure of cell wall polysaccharides that subsequently impaired the cellular elongation of floral styles and filaments, the germination of pollen grains, and the growth of pollen tubes. Consequently, plants overexpressing PAE1 exhibited severe male sterility. Furthermore, in contrast to the conventional view, PAE1-mediated deacetylation substantially lowered the digestibility of pectin. Our data suggest that pectin acetylesterase functions as an important structural regulator in planta by modulating the precise status of pectin acetylation to affect the remodeling and physiochemical properties of the cell wall's polysaccharides, thereby affecting cell extensibility.

Golgi-Mediated Synthesis and Secretion of Matrix Polysaccharides of the Primary Cell Wall of Higher Plants

The Golgi apparatus of eukaryotic cells is known for its central role in the processing, sorting, and transport of proteins to intra- and extra-cellular compartments. In plants, it has the additional task of assembling and exporting the non-cellulosic polysaccharides of the cell wall matrix including pectin and hemicelluloses, which are important for plant development and protection. In this review, we focus on the biosynthesis of complex polysaccharides of the primary cell wall of eudicotyledonous plants. We present and discuss the compartmental organization of the Golgi stacks with regards to complex polysaccharide assembly and secretion using immuno-electron microscopy and specific antibodies recognizing various sugar epitopes. We also discuss the significance of the recently identified Golgi-localized glycosyltransferases responsible for the biosynthesis of xyloglucan (XyG) and pectin.

Functional characterization and oligomerization of a recombinant xyloglucan-specific endo-β-1,4-glucanase (GH12) from Aspergillus niveus

Xyloglucan is a major structural polysaccharide of the primary (growing) cell wall of higher plants. It consists of a cellulosic backbone (beta-1,4-linked glucosyl residues) that is frequently substituted with side chains. This report describes Aspergillus nidulans strain A773 recombinant secretion of a dimeric xyloglucan-specific endo-β-1,4-glucanohydrolase (XegA) cloned from Aspergillus niveus. The ORF of the A. niveus xegA gene is comprised of 714 nucleotides, and encodes a 238 amino acid protein with a calculated molecular weight of 23.5kDa and isoelectric point of 4.38. The optimal pH and temperature were 6.0 and 60°C, respectively. XegA generated a xyloglucan-oligosaccharides (XGOs) pattern similar to that observed for cellulases from family GH12, i.e., demonstrating that its mode of action includes hydrolysis of the glycosidic linkages between glucosyl residues that are not branched with xylose. In contrast to commercial lichenase, mixed linkage beta-glucan (lichenan) was not digested by XegA, indicating that the enzyme did not cleave glucan β-1,3 or β-1,6 bonds. The far-UV CD spectrum of the purified enzyme indicated a protein rich in β-sheet structures as expected for GH12 xyloglucanases. Thermal unfolding studies displayed two transitions with mid-point temperatures of 51.3°C and 81.3°C respectively, and dynamic light scattering studies indicated that the first transition involves a change in oligomeric state from a dimeric to a monomeric form. Since the enzyme is a predominantly a monomer at 60°C, the enzymatic assays demonstrated that XegA is more active in its monomeric state.

Biochemical and Molecular Characterization of Secreted α-Xylosidase from Aspergillus niger

α-Linked xylose is a major component of xyloglucans in the cell walls of higher plants. An α-xylosidase (AxlA) was purified from a commercial enzyme preparation from Aspergillus niger, and the encoding gene was identified. The protein is a member of glycosyl hydrolase family 31. It was active on p-nitrophenyl-α-d-xyloside, isoprimeverose, xyloglucan heptasaccharide (XXXG), and tamarind xyloglucan. When expressed in Pichia pastoris, AxlA had activity comparable to the native enzyme on pNPαX and IP despite apparent hyperglycosylation. The pH optimum of AxlA was between 3.0 and 4.0. AxlA together with β-glucosidase depolymerized xyloglucan heptasaccharide. A combination of AxlA, β-glucosidase, xyloglucanase, and β-galactosidase in the optimal proportions of 51:5:19:25 or 59:5:11:25 could completely depolymerize tamarind XG to free Glc or Xyl, respectively. To the best of our knowledge, this is the first characterization of a secreted microbial α-xylosidase. Secreted α-xylosidases appear to be rare in nature, being absent from other tested commercial enzyme mixtures and from the genomes of most filamentous fungi.

Endo-β-1,3-galactanase from Winter Mushroom Flammulina velutipes

Arabinogalactan proteins are proteoglycans found on the cell surface and in the cell walls of higher plants. The carbohydrate moieties of most arabinogalactan proteins are composed of β-1,3-galactan main chains and β-1,6-galactan side chains, to which other auxiliary sugars are attached. For the present study, an endo-β-1,3-galactanase, designated FvEn3GAL, was first purified and cloned from winter mushroom Flammulina velutipes. The enzyme specifically hydrolyzed β-1,3-galactan, but did not act on β-1,3-glucan, β-1,3:1,4-glucan, xyloglucan, and agarose. It released various β-1,3-galactooligosaccharides together with Gal from β-1,3-galactohexaose in the early phase of the reaction, demonstrating that it acts on β-1,3-galactan in an endo-fashion. Phylogenetic analysis revealed that FvEn3GAL is member of a novel subgroup distinct from known glycoside hydrolases such as endo-β-1,3-glucanase and endo-β-1,3:1,4-glucanase in glycoside hydrolase family 16. Point mutations replacing the putative catalytic Glu residues conserved for enzymes in this family with Asp abolished activity. These results indicate that FvEn3GAL is a highly specific glycoside hydrolase 16 endo-β-1,3-galactanase.

Effects of xyloglucan with the partial removal of galactose on plasma lipid concentration

Xyloglucan is a component of the cell walls of higher plants that has been used as a thickener or stabilizer in the food industry in Japan and other Asian countries. Xyloglucan from which side-chain galactose has been partially removed or ‘trimmed’ by β-galactosidase (GXG-TG) shows heat-induced reversible gelation, and reverts to sol upon cooling. Xyloglucan is not digested by human digestive enzymes and acts as a dietary fiber. The effects of xyloglucan from which galactose has been partially removed on plasma lipid concentration in rats was investigated. Male Wistar rats (4 weeks old) were fed a high-fat diet (corn oil or lard) for 28 days (control) and other groups were given a high-fat diet (corn oil or lard) containing GXG-TG (5%, replacing cellulose). GXG-TG significantly reduced total cholesterol, β-lipoprotein, total lipid and phospholipid compared to a high-fat diet with corn oil. GXG-TG significantly reduced total cholesterol, β-lipoprotein, total lipid, phospholipid and adipose tissue weight compared to a high-fat diet with lard. These results indicated that the intake of GXG-TG improves lipid metabolism in rats, similar to that of the intact xyloglucan.

Deep sequencing of voodoo lily (Amorphophallus konjac): an approach to identify relevant genes involved in the synthesis of the hemicellulose glucomannan

A Roche 454 cDNA deep sequencing experiment was performed on a developing corm of Amorphophallus konjac—also known as voodoo lily. The dominant storage polymer in the corm of this plant is the polysaccharide glucomannan, a hemicellulose known to exist in the cell walls of higher plants and a major component of plant biomass derived from softwoods. A total of 246 mega base pairs of sequence data was obtained from which 4,513 distinct contigs were assembled. Within this voodoo lily expressed sequence tag collection genes representing the carbohydrate related pathway of glucomannan biosynthesis were identified, including sucrose metabolism, nucleotide sugar conversion pathways for the formation of activated precursors as well as a putative glucomannan synthase. In vivo expression of the putative glucomannan synthase and subsequent in vitro activity assays unambiguously demonstrate that the enzyme has indeed glucomannan mannosyl- and glucosyl transferase activities. Based on the expressed sequence tag analysis hitherto unknown pathways for the synthesis of GDP-glucose, a necessary precursor for glucomannan biosynthesis, could be proposed. Moreover, the results highlight transcriptional bottlenecks for the synthesis of this hemicellulose.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-011-1422-z) contains supplementary material, which is available to authorized users.

Impact of beta-glucan on the faecal microbiota of polypectomized patients: A pilot study

Beta-glucans are polysaccharides present in the cell walls of higher plants, in the seeds of some cereals, and certain yeasts and fungi also produce them. It is suggested that they exhibit, among many other health benefits, protective effects against carcinogenesis in the colon, but there is not enough human data to support this. The aim of the study was to determine the effect of barley-derived beta-glucan in the gut microbiota of polypectomized patients. Subjects were randomly assigned to consume 125 g of bread per day with beta-glucan (3 g/d), or without (placebo group), for 3 months. Thirty-three polypectomized men and women (mean age 57.6 years) were recruited into the study, but only 20 completed. Subjects did not consume any probiotics, prebiotics or antibiotics 2 months prior the intervention, or during the study. Stool samples were collected at baseline, on days 30 and 90 of intervention, as well as 2 weeks after the intervention, for enumeration of total aerobes and anaerobes, coliforms, E. coli, enterococci, Bacteroides spp., Clostridium perfringens, bifidobacteria, lactobacilli and Candida spp. Faecal bacterial enzyme activity (beta-glucuronidase and beta-glucosidase), pH, faecal moisture and the concentration of volatile fatty acids in the faeces were measured. Gastrointestinal symptoms were also recorded. Overall, no significant differences were observed in bacterial viable counts between the two feeding groups. Group specific analysis for β-glucan group revealed significantly decreased total coliform counts on the 30th day of the trial compared to the baseline ( p = 0.041). Clostridium perfringens concentration increased without reaching statistical significance, on the 30th day, while it decreased significantly on the 90th day of the intervention compared to the 30th day ( p = 0.016). An increase was noted in the molar ratio of acetate on the 90th day of the trial compared to placebo ( p = 0.018). The molar ratio of butyrate presented a trend to increase on the 30th day, which decreased ( p = 0.013) on the 90th day and then increase 2 weeks after the intervention ( p = 0.017) compared to placebo. A decrease was recorded in the β-glucan group in the bloating and abdominal pain score after the 30th day of the intervention (Day 30–37) compared to placebo. During β-glucan administration we did not observe any changes on beta-glucuronidase or beta-glucosidase activity, faecal pH, or on faecal moisture.

High-resolution structure of exo-arabinanase fromPenicillium chrysogenum

Arabinanase Abnx from Penicillium chrysogenum 31B, which belongs to the GH93 family, releases arabinobiose from the nonreducing terminus of α-1,5-L-arabinan, which is distributed in the primary cell walls of higher plants. Crystal structures of Abnx and of its complex with arabinobiose were determined at the high resolutions of 1.14 Å to an R(work) of 10.7% (R(free) = 12.8%) and 1.04 Å to an R(work) of 10.4% (R(free) = 12.5%). Abnx has a six-bladed β-propeller fold with a typical ring-closure mode called `Velcro', in which the last four-stranded β-sheet iscompleted by the incorporation of a strand from the N-terminus. Catalytic residues which act as a nucleophile and an acid/base were proposed from the structures and confirmed by site-directed mutagenesis. The substrate-binding groove is enclosed at one end by two residues, Glu64 and Tyr66, which contribute to the recognition of the nonreducing chain end ofthe polysaccharide. A comparison with the related enzyme Arb93A which has a quite similar overall structure suggested that Abnx has different mechanisms to funnel substrates to the active site and/or to stabilize the transition state.

Protecting Innovation: Genomics-Based Intellectual Property for the Development of Feedstock for Second-Generation Biofuels

One of the many controversies surrounding large-scale biofuel production is the diversion of land and other resources that might otherwise be used for food crops. Recent innovations will lead to a second generation of biofuel crops that can co-exist with food crops with little or no competition. Feedstocks from these bio-energy crops will be used to produce liquid fuel from cellulose, the most abundant polymer on the planet. Cell walls of higher plants are mainly composed of cellulose, hemicellulose, and lignin polymers. Cellulose and hemicellulose are polysaccharides with obvious value for biofuel production. However, lignin, while vital for plant growth and development, is widely known to negatively impact conversion efficiencies. Biomass pre-treatment, which is aimed at lignin removal, is not straightforward, and presents one of the major scientific and technical challenges and expenses associated with secondgeneration biofuel production. Scientific breakthroughs associated with altering the expression of key genes in the lignin biosynthetic pathway of biomass crops is a promising path toward solving this problem, and will likely impact the feedstock patent landscape in the near future. This review summarizes some of the recent and most important issued patents and patent applications associated with lignin-modification genes and methods of developing transgenic plants with altered lignin content and composition.

Arabinogalactan-Proteins in The Evolution of Gravity Resistance in Land Plants

The cell walls of land plants developed under the influence of earth's gravity. Arabinogalactan-proteins (AGPs) are a family of proteoglycans that localize on plasma membranes and in cell walls of higher plants. Recent studies have revealed that the expression levels of genes encoding the core proteins of AGPs are modified by hypergravity, indicating the involvement of AGPs in gravity resistance. A BLAST search in the genome databases of various organisms for genes encoding proteins related to fasciclin-like AGPs (FLAs), found FLAs in land plants including a moss, Physcomitrella patens subsp. patens, but not in the green algae, Chlamydomonas reinhardtii or Volvox carteri. On the other hand, the backbone structure of arabinogalactan moieties of AGPs, β-1,3:1,6-galactan, is widely distributed among organisms and has been confirmed in a species of Chlorellaceae, a snail and a mammal. These facts suggest that acquisition of some AGPs similar to those currently found, and FLAs in particular, was important in the evolution of the resistance of plants to gravitational force. By studying the molecular functions of AGPs under diverse gravitational conditions, we should be able to deepen our understanding of the evolutional process that turned aquatic organisms into terrestrial plants.