Fern cell walls and the evolution of arabinogalactan proteins in streptophytes.

Significant changes have occurred in plant cell wall composition during evolution and diversification of tracheophytes. As the sister lineage to seed plants, knowledge on the cell wall of ferns is key to track evolutionary changes across tracheophytes and to understand seed plant-specific evolutionary innovations. Fern cell wall composition is not fully understood, including limited knowledge of glycoproteins such as the fern arabinogalactan proteins (AGPs). Here, we characterize the AGPs from the leptosporangiate fern genera Azolla, Salvinia, and Ceratopteris. The carbohydrate moiety of seed plant AGPs consists of a galactan backbone including mainly 1,3- and 1,3,6-linked pyranosidic galactose, which is conserved across the investigated fern AGPs. Yet, unlike AGPs of angiosperms, those of ferns contained the unusual sugar 3-O-methylrhamnose. Besides terminal furanosidic arabinose, Ara (Araf), the main linkage type of Araf in the ferns was 1,2-linked Araf, whereas in seed plants 1,5-linked Araf is often dominating. Antibodies directed against carbohydrate epitopes of AGPs supported the structural differences between AGPs of ferns and seed plants. Comparison of AGP linkage types across the streptophyte lineage showed that angiosperms have rather conserved monosaccharide linkage types; by contrast bryophytes, ferns, and gymnosperms showed more variability. Phylogenetic analyses of glycosyltransferases involved in AGP biosynthesis and bioinformatic search for AGP protein backbones revealed a versatile genetic toolkit for AGP complexity in ferns. Our data reveal important differences across AGP diversity of which the functional significance is unknown. This diversity sheds light on the evolution of the hallmark feature of tracheophytes: their elaborate cell walls.

Search for evolutionary roots of land plant arabinogalactan-proteins in charophytes: presence of a rhamnogalactan-protein in Spirogyra pratensis (Zygnematophyceae).

Charophyte green algae (CGA) are assigned to be the closest relatives of land plants and therefore enlighten processes in the colonization of terrestrial habitats. For the transition from water to land, plants needed significant physiological and structural changes, as well as with regard to cell wall composition. Sequential extraction of cell walls of Nitellopsis obtusa (Charophyceae) and Spirogyra pratensis (Zygnematophyceae) offered a comparative overview on cell wall composition of late branching CGA. Because arabinogalactan-proteins (AGPs) are considered common for all land plant cell walls, we were interested in whether these special glycoproteins are present in CGA. Therefore, we investigated both species with regard to characteristic features of AGPs. In the cell wall of Nitellopsis, no hydroxyproline was present and no AGP was precipitable with the ß-glucosyl Yariv's reagent (ßGlcY). By contrast, ßGlcY precipitation of the water-soluble cell wall fraction of Spirogyra yielded a glycoprotein fraction rich in hydroxyproline, indicating the presence of AGPs. Putative AGPs in the cell walls of non-conjugating Spirogyra filaments, especially in the area of transverse walls, were detected by staining with ßGlcY. Labelling increased strongly in generative growth stages, especially during zygospore development. Investigations of the fine structure of the glycan part of ßGlcY-precipitated molecules revealed that the galactan backbone resembled that of AGPs with 1,3- 1,6- and 1,3,6-linked Galp moieties. Araf was present only in small amounts and the terminating sugars consisted predominantly of pyranosidic terminal and 1,3-linked rhamnose residues. We introduce the term 'rhamnogalactan-protein' for this special AGP-modification present in S. pratensis.

The cell walls of different Chara species are characterized by branched galactans rich in 3-O-methylgalactose and absence of AGPs.

Streptophyte algae are the closest relatives to land plants; their latest common ancestor performed the most drastic adaptation in plant evolution around 500 million years ago: the conquest of land. Besides other adaptations, this step required changes in cell wall composition. Current knowledge on the cell walls of streptophyte algae and especially on the presence of arabinogalactan-proteins (AGPs), important signalling molecules in all land plants, is limited. To get deeper insights into the cell walls of streptophyte algae, especially in Charophyceae, we performed sequential cell wall extractions of four Chara species. The three species Chara globularis, Chara subspinosa and Chara tomentosa revealed comparable cell wall compositions, with pectins, xylans and xyloglucans, whereas Chara aspera stood out with higher amounts of uronic acids in the pectic fractions and lack of reactivity with antibodies binding to xylan- and xyloglucan epitopes. Search for AGPs in the four Chara species and in Nitellopsis obtusa revealed the presence of galactans with pyranosidic galactose in 1,3-, 1,6- and 1,3,6-linkage, which are typical galactan motifs in land plant AGPs. A unique feature of these branched galactans was high portions of 3-O-methylgalactose. Only Nitellopsis contained substantial amounts of arabinose A bioinformatic search for prolyl-4-hydroxylases, involved in the biosynthesis of AGPs, revealed one possible functional sequence in the genome of Chara braunii, but no hydroxyproline could be detected in the four Chara species or in Nitellopsis obtusa. We conclude that AGPs that is typical for land plants are absent, at least in these members of the Charophyceae.

Profiling the cell walls of seagrasses from A (Amphibolis) to Z (Zostera).

BACKGROUND: The polyphyletic group of seagrasses shows an evolutionary history from early monocotyledonous land plants to the marine environment. Seagrasses form important coastal ecosystems worldwide and large amounts of seagrass detritus washed on beaches might also be valuable bioeconomical resources. Despite this importance and potential, little is known about adaptation of these angiosperms to the marine environment and their cell walls. RESULTS: We investigated polysaccharide composition of nine seagrass species from the Mediterranean, Red Sea and eastern Indian Ocean. Sequential extraction revealed a similar seagrass cell wall polysaccharide composition to terrestrial angiosperms: arabinogalactans, pectins and different hemicelluloses, especially xylans and/or xyloglucans. However, the pectic fractions were characterized by the monosaccharide apiose, suggesting unusual apiogalacturonans are a common feature of seagrass cell walls. Detailed analyses of four representative species identified differences between organs and species in their constituent monosaccharide composition and lignin content and structure. Rhizomes were richer in glucosyl units compared to leaves and roots. Enhalus had high apiosyl and arabinosyl abundance, while two Australian species of Amphibolis and Posidonia, were characterized by high amounts of xylosyl residues. Interestingly, the latter two species contained appreciable amounts of lignin, especially in roots and rhizomes whereas Zostera and Enhalus were lignin-free. Lignin structure in Amphibolis was characterized by a higher syringyl content compared to that of Posidonia. CONCLUSIONS: Our investigations give a first comprehensive overview on cell wall composition across seagrass families, which will help understanding adaptation to a marine environment in the evolutionary context and evaluating the potential of seagrass in biorefinery incentives.

The cell wall of hornworts and liverworts: innovations in early land plant evolution?

An important step for plant diversification was the transition from freshwater to terrestrial habitats. The bryophytes and all vascular plants share a common ancestor that was probably the first to adapt to life on land. A polysaccharide-rich cell wall was necessary to cope with newly faced environmental conditions. Therefore, some pre-requisites for terrestrial life have to be shared in the lineages of modern bryophytes and vascular plants. This review focuses on hornwort and liverwort cell walls and aims to provide an overview on shared and divergent polysaccharide features between these two groups of bryophytes and vascular plants. Analytical, immunocytochemical, and bioinformatic data were analysed. The major classes of polysaccharides-cellulose, hemicelluloses, and pectins-seem to be present but have diversified structurally during evolution. Some polysaccharide groups show structural characteristics which separate hornworts from the other bryophytes or are too poorly studied in detail to be able to draw absolute conclusions. Hydroxyproline-rich glycoprotein backbones are found in hornworts and liverworts, and show differences in, for example, the occurrence of glycosylphosphatidylinositol (GPI)-anchored arabinogalactan-proteins, while glycosylation is practically unstudied. Overall, the data are an appeal to researchers in the field to gain more knowledge on cell wall structures in order to understand the changes with regard to bryophyte evolution.

Degraded Arabinogalactans and Their Binding Properties to Cancer-Associated Human Galectins.

Galectins represent ß-galactoside-binding proteins with numerous functions. Due to their role in tumor progression, human galectins-1, -3 and -7 (Gal-1, -3 and -7) are potential targets for cancer therapy. As plant derived glycans might act as galectin inhibitors, we prepared galactans by partial degradation of plant arabinogalactan-proteins. Besides commercially purchased galectins, we produced Gal-1 and -7 in a cell free system and tested binding capacities of the galectins to the galactans by biolayer-interferometry. Results for commercial and cell-free expressed galectins were comparable confirming functionality of the cell-free produced galectins. Our results revealed that galactans from Echinacea purpurea bind to Gal-1 and -7 with KD values of 1-2 µM and to Gal-3 slightly stronger with KD values between 0.36 and 0.70 µM depending on the sensor type. Galactans from the seagrass Zostera marina with higher branching of the galactan and higher content of uronic acids showed stronger binding to Gal-3 (0.08-0.28 µM) compared to galactan from Echinacea. The results contribute to knowledge on interactions between plant polysaccharides and galectins. Arabinogalactan-proteins have been identified as a new source for production of galactans with possible capability to act as galectin inhibitors.

Allergy-Protective Arabinogalactan Modulates Human Dendritic Cells via C-Type Lectins and Inhibition of NF-κB.

Arabinogalactan (AG) isolated from dust of a traditional farm prevents disease in murine models of allergy. However, it is unclear whether this polysaccharide has immune regulatory properties in humans. The aim of this study was to test the influence of AG on the immune-stimulating properties of human dendritic cells (DCs). Moreover, we sought to identify the receptor to which AG binds. AG was produced from plant callus tissue under sterile conditions to avoid the influence of pathogen-associated molecular patterns in subsequent experiments. The influence of AG on the human immune system was investigated by analyzing its impact on monocyte-derived DCs. To analyze whether the T cell stimulatory capacity of AG-stimulated DCs is altered, an MLR with naive Th cells was performed. We revealed that AG reduced T cell proliferation in a human MLR. In the search for a molecular mechanism, we found that AG binds to the immune modulatory receptors DC-specific ICAM-3 -: grabbing non integrin (DC-SIGN) and macrophage mannose receptor 1 (MMR-1). Stimulation of these receptors with AG simultaneously with TLR4 stimulation with LPS increased the expression of the E3 ubiquitin-protein ligase tripartite motif -: containing protein 21 and decreased the phosphorylation of NF-κB p65 in DCs. This led to a reduced activation profile with reduced costimulatory molecules and proinflammatory cytokine production. Blocking of MMR-1 or DC-SIGN with neutralizing Abs partially inhibits this effect. We conclude that AG dampens the activation of human DCs by LPS via binding to DC-SIGN and MMR-1, leading to attenuated TLR signaling. This results in a reduced T cell activation capacity of DCs.

Reproduction of the Medicinal Plant Pelargonium sidoides via Somatic Embryogenesis.

The medicinal plant Pelargonium sidoides DC. (Geraniaceae) was traditionally used for the treatment of the common cold and cough in South Africa. Today an aequous-ethanolic root extract from this plant is approved for the treatment of acute bronchitis and is globally marketed also as an immunostimulant. The increasing demand of the plant material for the industrial production indicates the need of new effective methods for the propagation of P. sidoides. Here we report somatic embryogenesis and in vitro plantlet regeneration from somatic cells of inflorescence shoots and petioles of P. sidoides. A one-week cultivation of explants in media containing different concentrations of thidiazuron (1, 2.2, 3, and 4 mg/L) followed by a cultivation period without phytohormones resulted in the induction of somatic embryos within 2-4 weeks. After 2-4 months, the embryos generated roots and could be transferred into a greenhouse, where flower formation took place and the development of seeds occurred with high germination rates. The root umckalin concentration, determined by high-performance thin-layer chromatography, was comparable to that of seed-cultivated plants (100 ± 6 vs. 113 ± 10 µg umckalin/g dried roots). For the first time, direct somatic embryogenesis has been established as an appropriate cultivation method for P. sidoides plants used as raw material in the pharmaceutical industry. Moreover, genetically identical plants (chemical races) can be easily generated by this procedure.

Studies on Unprocessed and Acid-Treated Arabinogalactan from Larch as an Inhibitor of Glycan Binding of a Plant Toxin and Biomedically Relevant Human Lectins.

The increasing evidence for the physiological significance of glycan-protein (lectin) interactions prompts considerations for respective bioactivity of plant polysaccharides. Arabinogalactan from larch, a polysaccharide with a ß1,3-linked galactose core and branches at the 6'-hydroxyl, was thus tested, together with two processed forms treated either with oxalic or trifluoroacetic acid. Hydrolysis by acid reduced the arabinose contents without backbone degradation. The three preparations were tested as an inhibitor of lectin binding in solid-phase and cell-based assays, using the toxin from Viscum album and a panel of seven human lectins (six galectins and a C-type lectin). Increasing potency correlating with the molecular contents of galactose was seen for the plant toxin. In general, relatively weak or no inhibitory capacity was detected for the three preparations, when binding of the human galectins and avian orthologues used as controls was measured. Acid-treated polysaccharides also weakly interfered with binding of the galactose-specific C-type lectin of human macrophages. Larch arabinogalactan, tested as a model, will thus most likely not impair (ga)lectin functionality physiologically.

Antibodies against Yariv's reagent for immunolocalization of arabinogalactan-proteins in aerial parts of Echinacea purpurea.

Arabinogalactan-proteins are glycoproteins that occur in higher plants and are involved in important processes like cell differentiation and plant growth. In the medicinal plant Echinacea purpurea L., they belong to the putative immunomodulating compounds and are structurally well characterized. For microscopic localization of arabinogalactan-proteins, synthetic (ß-D-Glc)3 Yariv phenylglycoside that specifically binds to most plant arabinogalactan-proteins was used to label arabinogalactan-proteins in fresh cut sections of stems and petioles of Echinacea purpurea. Polyclonal antibodies against (ß-D-Glc)3 Yariv phenylglycoside were used to detect the arabinogalactan-protein-(ß-D-Glc)3 Yariv phenylglycoside complex. After addition of fluorescein isothiocyanate-conjugated secondary antibodies, the sections were analyzed by confocal laser scanning microscopy. Arabinogalactan-proteins are localized mainly in the central cylinder in the collateral vascular bundles, especially in the area of the xylem. In cell walls of fully differentiated vessels and tracheids, arabinogalactan-proteins have been detected mainly at the inner area of the wall close to the cell lumina. Intense labeling occurs around pit canals connecting adjacent vessels. Furthermore, arabinogalactan-proteins are present in the lumina of cells of the sclerenchyma caps and in companion cells of the phloem.

Arabinogalactan-proteins from non-coniferous gymnosperms have unusual structural features.

Arabinogalactan-proteins (AGPs), important signalling molecules of the plant cell wall, are structurally extensively investigated in angiosperms, but information on AGPs in gymnosperms is still limited. We characterized AGPs from the gymnosperms Ginkgo biloba, Ephedra distachya, Encephalartos longifolius and Cycas revoluta. The protein contents are comparable to that of angiosperm AGPs. Hydroxyproline is the site of linking the carbohydrate part and was detected in all AGPs with highest concentration in Cycas AGP (1.1 % of the AGP). Interestingly, with the exception of Cycas, all AGPs contained the monosaccharide 3-O-methylrhamnose not present in angiosperm polysaccharides. The carbohydrate moieties of Cycas and Ephredra showed the main components 1,3,6-linked galactose and terminal arabinose typical of angiosperm AGPs, whereas that of Ginkgo AGP was unique with 1,4-linked galactose as dominant structural element. Bioinformatic search for glycosyltransferases in Ginkgo genome also revealed a lower number of galactosyltransferases responsible for biosynthesis of the 1,3-Gal/1,6-Gal AGP backbone.

The Cell Wall of Seagrasses: Fascinating, Peculiar and a Blank Canvas for Future Research.

Seegrasses are a polyphyletic group of angiosperm plants, which evolved from early monocotyledonous land plants and returned to the marine environment around 140 million years ago. Today, seagrasses comprise the five families Zosteraceae, Hydrocharitaceae, Posidoniaceae, Cymodoceaceae, and Ruppiaceae and form important coastal ecosystems worldwide. Despite of this ecological importance, the existing literature on adaption of these angiosperms to the marine environment and especially their cell wall composition is limited up to now. A unique feature described for some seagrasses is the occurrence of polyanionic, low-methylated pectins mainly composed of galacturonic acid and apiose (apiogalacturonans). Furthermore, sulfated galactans have been detected in some species. Recently, arabinogalactan-proteins (AGPs), highly glycosylated proteins of the cell wall of land plants, have been isolated for the first time from a seagrass of the baltic sea. Obviously, seagrass cell walls are characterized by new combinations of structural polysaccharide and glycoprotein elements known from macroalgae and angiosperm land plants. In this review, current knowledge on cell walls of seagrasses is summarized and suggestions for future investigations are given.

Arabinogalactan-proteins of Zostera marina L. contain unique glycan structures and provide insight into adaption processes to saline environments.

Seagrasses evolved from monocotyledonous land plants that returned to the marine habitat. This transition was accomplished by substantial changes in cell wall composition, revealing habitat-driven adaption to the new environment. Whether arabinogalactan-proteins (AGPs), important signalling molecules of land plants, are present in seagrass cell walls is of evolutionary and plant development interest. AGPs of Zostera marina L. were isolated and structurally characterised by analytical and bioinformatics methods as well as by ELISA with different anti-AGP antibodies. Calcium-binding capacity of AGPs was studied by isothermal titration calorimetry (ITC) and microscopy. Bioinformatic searches of the Z. marina proteome identified 9 classical AGPs and a large number of chimeric AGPs. The glycan structures exhibit unique features, including a high degree of branching and an unusually high content of terminating 4-O-methyl-glucuronic acid (4-OMe GlcA) residues. Although the common backbone structure of land plant AGPs is conserved in Z. marina, the terminating residues are distinct with high amounts of uronic acids. These differences likely result from the glycan-active enzymes (glycosyltransferases and methyltransferases) and are essential for calcium-binding properties. The role of this polyanionic surface is discussed with regard to adaption to the marine environment.

Plant-derived saccharides and their inhibitory potential on metastasis associated cellular processes of pancreatic ductal adenocarcinoma cells.

This study intends to investigate the inhibitory potential of different plant derived saccharides on cell migration and adhesion of pancreatic ductal adenocarcinoma (PDAC) cells to microvascular liver endothelium, particularly considering the role of transmembranous galectin-3. PDAC cell lines PancTu1 and Panc1 were characterized by considerable (transmembranous) galectin-3 (Gal3) expression. SiRNA mediated Gal3 knockdown as well as treatment with differentially processed pectins and arabinogalactan-proteins (AGPs) did not impact on cell migration of either PDAC cell line. In contrast, Gal3 knockdown reduced adhesion of PDAC cells to the liver endothelial cell line TMNK-1 being more pronounced in Panc1 cells. Similarly, plant derived substances did not impact cell adhesion of PancTu1 cells while partially hydrolyzed citrus pectin (MCP), pectinase-treated MCP (MCPPec) and partially hydrolized AGP (AGPTFA) clearly diminished adhesive properties of Panc1 cells. MCPPec or AGPTFA could not further intensify the adhesion reducing effect of galectin-3 knockdown, indicating that these plant derived polysaccharides are able to inhibit PDAC cell adhesion to liver endothelial cells in a galectin-3 dependent manner. Overall, these data suggest an inhibitory potential of plant derived processed saccharides which have undergone chemical modification in impairing PDAC cell adhesion to liver endothelium.

Characterization and immunolocalization of arabinogalactan-proteins in roots of Echinacea purpurea.

From the high molecular weight fraction of an aqueous extract from roots of Echinacea purpurea L. Moench, arabinogalactan-proteins (AGPs), a class of proteoglycans proposed to be involved in cell differentiation and plant growth, were purified and characterized with regard to amino acid composition and structure of the polysaccharide moiety. The protein content of the AGP was 5.0 % (w/w) with the dominating amino acids Glx, Hyp, Asx, Ser, Thr and Ala. The highly branched polysaccharide moiety shows a linkage composition typical of AGPs with 1,3-, 1,6- and 1,3,6-linked galactopyranosyl residues and arabinofuranosyl residues predominantly as terminal and 1,5-linked residues. Terminal units of glucuronopyranose acid were also detected. Furthermore, a new method for the localization of AGPs in plant tissue has been developed. The synthetic (beta- D-Glc)(3) Yariv phenylgycoside (betaGlcY) is known to specifically bind to AGPs. For immunolocalization, polyclonal betaGlcY-antibodies have been generated and were used to label Yariv-treated thin sections of roots from E. purpurea. After addition of the FITC-conjugated secondary antibody, the sections were analyzed by confocal laser scanning microscopy. AGPs are detected mainly in the central cylinder in the area of the xylem. Cell walls of vessels and tracheids are strongly labelled, especially at the inner area of the wall. Furthermore, there is intense labelling of the pit canals.

IgG stability in fresh and conditioned medium of tobacco (Nicotiana tabacum) and larch (Larix decidua) embryogenic suspension cultures.

To explore the feasibility of larch (Larix decidua Mill.) embryogenic cell culture as alternative plant expression system, protein stability in fresh and conditioned medium was characterized in this study and compared to tobacco BY2 suspension culture. Fresh and conditioned media were spiked with 1 microg human IgG and IgG content was determined by ELISA after 24 h incubation. In fresh media, IgG recovery rate decreased to 12-23%. Adsorption on vessel walls probably is the best explanation for this IgG loss and EDTA in the medium strongly influenced wall adsorption. A high IgG recovery rate occurred in all conditioned cell culture media (7 or 14 days after inoculation). Changes in the low molecular weight-constitution of conditioned medium, rather than co-secreted polymers, are responsible for IgG stability in the cell suspension cultures.

Arabinogalactan-Proteins from the Liverwort Marchantia polymorpha L., a Member of a Basal Land Plant Lineage, Are Structurally Different to Those of Angiosperms.

The thalloid liverwort Marchantia polymorpha as a member of a basal land plant lineage has to cope with the challenge of terrestrial life. Obviously, the plant cell wall has been strongly involved in the outstanding evolutionary process of water-to-land-transition. AGPs are signaling glycoproteins of the cell wall, which seem to be ubiquitous in seed plants and might play a role in adaption to abiotic and biotic stress situations. Therefore, we investigated the cell wall composition of Marchantia polymorpha with special focus on structural characterization of arabinogalactan-proteins. The Marchantia AGP shows typical features known from seed plant AGPs like precipitation with ß-glucosyl-Yariv's reagent, a protein moiety with hydroxyproline and a carbohydrate part with 1,3,6-linked galactose and terminal arabinose residues. On the other hand, striking differences to AGPs of angiosperms are the occurrence of terminal 3-O-methyl-rhamnose and a highly branched galactan lacking appreciable amounts of 1,6-linked galactose. Binding of different AGP-antibodies (JIM13, KM1, LM2, LM6, LM14, LM26, and MAC207) to Marchantia AGP was investigated and confirmed structural differences between liverwort and angiosperm AGP, possibly due to deviating functions of these signaling molecules in the different taxonomic groups.

Arabinogalactan-proteins in spore-producing land plants.

Arabinogalactan-proteins (AGPs) are proteoglycans of the extracellular matrix of plants that were first isolated and described in the 1970s. Today, the consensus is that the following features are regarded as typical for these molecules: In contrast to broad knowledge on AGPs in seed plants, insight in occurrence and structure of AGPs in spore-producing land plants (bryophytes, lycophytes and monilophytes) is very limited, although these plants are the closest living relatives to seed plants. In general, understanding of cell wall evolution is incomplete due to limited knowledge of cell wall structure of non-flowering plants. In this review, current knowledge on AGPs of mosses, clubmosses and ferns is summarized, possible functions are discussed and suggestions for future investigations are given.

Structural investigations on arabinogalactan-proteins from a lycophyte and different monilophytes (ferns) in the evolutionary context.

Today, understanding of cell wall evolution is incomplete due to limited knowledge of cell wall structure of non-flowering plants. Besides polysaccharides, proteoglycans like arabinogalactan-proteins are important constituents of the cell wall of most if not all seed plants. This article provides the first detailed characterization of AGPs from a lycophyte and different ferns, which are the closest living relatives to seed plants. The amount of protein in fern AGPs (6-12%) was in a range comparable to most seed plant AGPs. However, it was higher for Lycopodium AGP (17%). The carbohydrate moieties of investigated AGPs showed typical features known for type-II arabinogalactans from seed plants and showed cross-reaction with polyclonal antibodies raised against Echinacea AGP. On the other hand, unusual structural components like high quantities of pyranosidic arabinose residues for Lycopodium AGP and 3-O-methyl-rhamnose for fern AGPs have been detected.

Evolution of plant cell wall: Arabinogalactan-proteins from three moss genera show structural differences compared to seed plants.

Arabinogalactan-proteins (AGPs) are important proteoglycans of plant cell walls. They seem to be present in most, if not all seed plants, but their occurrence and structure in bryophytes is widely unknown and actually the focus of AGP research. With regard to evolution of plant cell wall, we isolated AGPs from the three mosses Sphagnum sp., Physcomitrella patens and Polytrichastrum formosum. The moss AGPs show structural characteristics common for AGPs of seed plants, but also unique features, especially 3-O-methyl-rhamnose (trivial name acofriose) as terminal monosaccharide not found in arabinogalactan-proteins of angiosperms and 1,2,3-linked galactose as branching point never found in arabinogalactan-proteins before.