Distribution of mycolaminarans and cell wall β-glucans in the life cycle ofPhytophthora

Clinical and Physiological Perspectives of β-Glucans: The Past, Present, and Future

β-Glucans are a group of biologically-active fibers or polysaccharides from natural sources with proven medical significance. β-Glucans are known to have antitumor, anti-inflammatory, anti-obesity, anti-allergic, anti-osteoporotic, and immunomodulating activities. β-Glucans are natural bioactive compounds and can be taken orally, as a food supplement, or as part of a daily diet, and are considered safe to use. The medical significance and efficiency of β-glucans are confirmed in vitro, as well as using animal- and human-based clinical studies. However, systematic study on the clinical and physiological significance of β-glucans is scarce. In this review, we not only discuss the clinical and physiological importance of β-glucans, we also compare their biological activities through the existing in vitro and animal-based in vivo studies. This review provides extensive data on the clinical study of β-glucans.

Elevated amino acid biosynthesis in Phytophthora infestans during appressorium formation and potato infection

Appressorium formation is believed to be an important event in establishing a successful interaction between the late blight pathogen, Phytophthora infestans, and its host plants potato and tomato. An understanding of molecular events occurring in appressorium development could suggest new strategies for controlling late blight. We used parallel studies of the transcriptome and proteome to identify genes and proteins that are up-regulated in germinating cysts developing appressoria. As a result, five distinct genes involved in amino acid biosynthesis were identified that show increased expression in germinating cysts with appressoria. These are a methionine synthase (Pi-met1), a ketol-acid reductoisomerase (Pi-kari1), a tryptophan synthase (Pi-trp1), an acetolactate synthase (Pi-als1), and a threonine synthase (Pi-ts1). Four of these P. infestans genes were also up-regulated, although to lower levels, during the early, biotrophic phase of the interaction in potato and all five were considerably up-regulated during the transition (48 hpi) to the necrotrophic phase of the interaction. Real-time RT-PCR revealed that expression of potato homologues of the amino acid biosynthesis genes increased during biotrophic and necrotrophic infection phases. Furthermore, we investigated levels of free amino acids in the pre-infection stages and found that in most cases there was a decrease in free amino acids in zoospores and germinating cysts, relative to sporangia, followed by a sharp increase in germinating cysts with appressoria. Amino acid biosynthesis would appear to be important for pathogenicity in P. infestans, providing a potential metabolic target for chemical control.

Characterization of 1,3-beta-glucanase and 1,3;1,4-beta-glucanase genes from Phytophthora infestans

Three putative exo-1,3-beta-glucanase genes (Piexo1, Piexo2, Piexo3), one endo-1,3-beta-glucanase (Piendo1) and one endo-1,3;1,4-beta-glucanase (Piendo2) gene were cloned and characterized from the oomycete Phytophthora infestans. Southern hybridization revealed that Piexo1, Piexo2, Piexo3, and Piendo2 are single copy, and that Piendo1 is encoded by two copies. Furthermore, the analyses showed that for each gene, one or two closely related gene family members were present. The genes contain no introns. Nucleotide sequence analysis of the promoter regions (200nt upstream of ATG start codon) showed that the regions have 56-81% similarity to a 16-nt core sequence hypothesized to be the initiation of transcription point in oomycetes. The predicted molecular weights (32-83kDa), iso-electric points (4.2-6.7) and amino acid sequences of the five proteins are diverse. All the genes are expressed in in vitro grown mycelia and sporangia, as well as during infection of potatoes. Further, Piendo1 and Piendo2 are also expressed in germinating cysts, and Piendo2 in zoospores.

Production of extracellular matrices during development of infection structures by the downy mildew Peronospora parasitica

•  Differences are shown here in the structure and composition of the extracellular matrices surrounding conidia, germ-tubes and appressoria of the downy mildew Peronospora parasitica, which is a serious pathogen of several cultivated Brassica spp. •  The extracellular matrices of germlings growing in vitro (glass and polycarbonate substrata) were investigated using freeze-substitution transmission electron microscopy, lectin cytochemistry and immunogold labelling. •  The cell surface carbohydrates present on P. parasitica conidia differed markedly from those on germ-tubes and appressoria. The conidial cell wall comprised an inner electron-lucent layer containing β-1,3-glucans, and an outer electron-opaque layer containing carbohydrates recognized by Bauhinia purpurea agglutinin. •  Germ-tubes and appressoria release two types of extracellular matrix: a fibrillar matrix containing β-1,3-glucans is confined to the germling-substratum interface; a second matrix containing protein spreads beyond the contact interface as a thin film. The tenacious adherence of both types of matrix to the substratum after mechanical removal of the germlings suggests that they may contribute to germling attachment.

Pythium aphanidermatum: culture, cell-wall composition, and isolation and structure of antitumour storage and solubilised cell-wall (1----3),(1----6)-beta-D-glucans

Under optimal conditions for the culture of the fungus Phytium aphanidermatum, no polysaccharides were excreted into the medium. The mycelium contained up to 38% of a slightly branched, storage (1----3),(1----6)-beta-D-glucan with a MW of 20,000. The cell-wall polysaccharides of the mycelium comprised 18% of cellulose and 82% of (1----3),(1----6)-beta-D-glucans. Of the non-cellulosic glucans, approximately 33% could be solubilised by extraction with water at 121 degrees, and they had a MW of 10,000, were highly branched, and contained 6% of (1----6) linkages. Treatment of the cell wall with 0.1 M trifluoroacetic acid released approximately 50% of the non-cellulosic glucans. The acid-soluble cell-wall (1----3),-(1----6)-beta-D-glucans of lower MW (6000) were still highly branched and contained 14% of (1----6) and 8% of (1----4) linkages. The storage glucan and the hot-water-soluble cell-wall glucan exhibited strong activity against the Sarcoma 180 in CD-1 mice, whereas the acid-soluble cell-wall glucans were inactive. The hot-water-soluble cell-wall glucan was also active against the DBA/2-MC.SC-1 fibrosarcoma in DBA/2 mice.

Biosynthesis of beta-glucans in fungi

Glucans are the most abundant polysaccharides present in fungi. The present review provides updated information on the structure and synthesis of beta-glucans in fungal cells. Synthesis of these polymers made up of B1,3 chains with a variable degree of B1,6 branching involves several reactions: initiation, chain elongation and branching, of which the most studied one is the elongation step. This reaction, catalyzed by the so-called glucan synthetases, utilizes UDPG as sugar donor. Properties of glucan synthetases are extremely variable depending on the fungal species, and their developmental stage. Because of the importance of these polysaccharides it is anticipated that comprehension of their mechanism of synthesis, is important for the understanding of cell wall assembly and cell growth and morphogenesis, as well as for the design of specific antifungal drugs.

Growth characteristics on cellobiose of three different anaerobic fungi isolated from the ovine rumen

Three morphologically different anaerobic fungi, a Neocallimastix sp. strain (LM-1), a Piromonas sp. strain (SM-1), and a Sphaeromonas sp. strain (NM-1), were isolated from the rumens of sheep. Growth studies were conducted with each isolate in batch cultures by using an anaerobic semidefined medium that lacked ruminal fluid and contained 0.5% cellobiose. Cultures were incubated for periods of up to 10 days, and fungal growth was assessed at regular intervals by dry weight measurements. Samples of fungal biomass were also analyzed for cell-associated protein and, after acid hydrolysis, for chitin as hexosamine. The isolates produced similar yields of dry weight and contained similar amounts of protein. However, strain LM-1 grew at a higher rate and contained less than half the level of chitin compared with the other two isolates. There were high positive correlations between chitin and protein for all three fungi, but comparisons of these parameters with dry weights were affected by the presence of variable amounts of storage carbohydrate. The amount of storage carbohydrate reached maximum levels in strain LM-1 during mid-growth phase and then quickly declined thereafter. When dry weight yields for strain LM-1 were adjusted for changes in storage carbohydrate, high positive correlations were obtained between dry weight and protein or chitin. The storage carbohydrate was probably an alpha-1,4-glucan with alpha-1,6 branches.