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PubMed2002

Induced systemic resistance (ISR) against pathogens in the context of induced plant defences.

Induced systemic resistance (ISR) of plants against pathogens is a widespread phenomenon that has been intensively investigated with respect to the underlying signalling pathways as well as to its potential use in plant protection. Elicited by a local infection, plants respond with a salicylic-dependent signalling cascade that leads to the systemic expression of a broad spectrum and long-lasting disease resistance that is efficient against fungi, bacteria and viruses. Changes in cell wall composition, de novo production of pathogenesis-related-proteins such as chitinases and glucanases, and synthesis of phytoalexins are associated with resistance, although further defensive compounds are likely to exist but remain to be identified. In this Botanical Briefing we focus on interactions between ISR and induced resistance against herbivores that is mediated by jasmonic acid as a central signalling molecule. While many studies report cross-resistance, others have found trade-offs, i.e. inhibition of one resistance pathway by the other. Here we propose a framework that explains many of the thus far contradictory results. We regard elicitation separately from signalling and from production, i.e. the synthesis of defensive compounds. Interactions on all three levels can act independently from each other.

Animals↗
PubMed2002

Molecular cloning and characterization of glucanase inhibitor proteins: coevolution of a counterdefense mechanism by plant pathogens.

A characteristic plant response to microbial attack is the production of endo-beta-1,3-glucanases, which are thought to play an important role in plant defense, either directly, through the degradation of beta-1,3/1,6-glucans in the pathogen cell wall, or indirectly, by releasing oligosaccharide elicitors that induce additional plant defenses. We report the sequencing and characterization of a class of proteins, termed glucanase inhibitor proteins (GIPs), that are secreted by the oomycete Phytophthora sojae, a pathogen of soybean, and that specifically inhibit the endoglucanase activity of their plant host. GIPs are homologous with the trypsin class of Ser proteases but are proteolytically nonfunctional because one or more residues of the essential catalytic triad is absent. However, specific structural features are conserved that are characteristic of protein-protein interactions, suggesting a mechanism of action that has not been described previously in plant pathogen studies. We also report the identification of two soybean endoglucanases: EGaseA, which acts as a high-affinity ligand for GIP1; and EGaseB, with which GIP1 does not show any association. In vitro, GIP1 inhibits the EGaseA-mediated release of elicitor-active glucan oligosaccharides from P. sojae cell walls. Furthermore, GIPs and soybean endoglucanases interact in vivo during pathogenesis in soybean roots. GIPs represent a novel counterdefensive weapon used by plant pathogens to suppress a plant defense response and potentially function as important pathogenicity determinants.

Amino Acid Sequence↗
PubMed2004

Paenibacillus isolates possess diverse dextran-degrading enzymes.

AIMS: To isolate and identify dextran-degrading organisms from sugar mill and compost samples, and to examine the diversity of the dextranolytic enzymes produced. METHODS AND RESULTS: Fifteen dextranolytic prokaryotes were purified at various temperatures from sugar-mill or compost samples, using indicator plates containing blue dextran. A 16S rRNA gene sequence analysis showed that 12 isolates purified at 40, 50 or 70 degrees C were closely aligned to Paenibacillus spp. The three isolates purified at 60 degrees C had identical 16S rDNA sequences, with highest affinity to Bacillus spp. Liquid culture of the 11 isolates purified at 40 or 50 degrees C produced dextranolytic activity in the spent media with maximal activity at 40 or 45 degrees C under the assay conditions used. Hydrolysis of blue dextran in activity gels showed that the 12 Paenibacillus isolates produced from one to five dextranolytic proteins, ranging from 70 to 120 kDa. Based on 16S rDNA sequence, growth habit in liquid culture and dextranolytic enzyme pattern, the 12 Paenibacillus-like isolates could be differentiated into six distinct groups, one of which was capable of growth at 70 degrees C. CONCLUSIONS: The Bacillales, especially the Paenibacillus, are a valuable environmental repository for dextranolytic enzymes of diverse size and potentially diverse activity. SIGNIFICANCE AND IMPACT OF THE STUDY: Dextranolytic enzymes produced by Paenibacillus spp. are an exploitable resource for those interested in modifying the structure of dextrans.

Bacillus↗
PubMed1982

Ontogenic development of the suppressed secondary response to native dextran.

The ontogenic development of the plaque-forming cell (PFC) response to the thymus-independent (TI) antigen alpha 1-6 native dextran B512 was studied to determine when the first minimal amounts of anti-dextran antibodies are formed. Substantial antibody responses to certain other TI polysaccharide antigens arise during the first month of life, whereas the development of the response to native dextran has been found to be conspicuously delayed in high-responder mice. Results indicated that CBA mice began to produce minimal amounts of anti-dextran antibodies between 15 and 21 days of age, and the development continued progressively until peak levels were reached at 90 days of age. The alpha 1-6 native dextran system is also one of the few murine models in which endogenous anti-idiotypic antibodies are formed subsequent to anti-dextran production. It has been shown that the anti-idiotypic antibodies are responsible for specific inhibition of secondary PFC responses to dextran. Suppression of the secondary response was used here to ascertain whether the initial low level of anti-dextran antibodies elicited in 15-day-old animals was sufficient to lead to inhibition of the secondary response. The approach confirmed the initiation of anti-dextran production at 15-21 days of age and indicated that the small amount of anti-dextran antibodies produced at this age was sufficient to induce the mechanism leading to suppression of the secondary response.

Age Factors↗
PubMed1974

Lectin binding saccharides on a parasitic protozoan.

Leishmania donovani promastigotes were specifically agglutinated by concanavalin A and phytohemagglutinin P. Somatic-somatic, flagellar-somatic, and flagellar-flagellar type agglutination was observed with the lectins. Enzyme-treated promastigotes gave reduced lectin agglutination reactions. The results suggest that complex saccharide moieties are randomly distributed on the surface of this organism.

Agglutination↗
PubMed2006

Functional analysis of the twin-arginine translocation pathway in Corynebacterium glutamicum ATCC 13869.

Compared to those of other gram-positive bacteria, the genetic structure of the Corynebacterium glutamicum Tat system is unique in that it contains the tatE gene in addition to tatA, tatB, and tatC. The tatE homologue has been detected only in the genomes of gram-negative enterobacteria. To assess the function of the C. glutamicum Tat pathway, we cloned the tatA, tatB, tatC, and tatE genes from C. glutamicum ATCC 13869 and constructed mutants carrying deletions of each tat gene or of both the tatA and tatE genes. Using green fluorescent protein (GFP) fused with the twin-arginine signal peptide of the Escherichia coli TorA protein, we demonstrated that the minimal functional Tat system required TatA and TatC. TatA and TatE provide overlapping function. Unlike the TatB proteins from gram-negative bacteria, C. glutamicum TatB was dispensable for Tat function, although it was required for maximal efficiency of secretion. The signal peptide sequence of the isomaltodextranase (IMD) of Arthrobacter globiformis contains a twin-arginine motif. We showed that both IMD and GFP fused with the signal peptide of IMD were secreted via the C. glutamicum Tat pathway. These observations indicate that IMD is a bona fide Tat substrate and imply great potential of the C. glutamicum Tat system for industrial production of heterologous folded proteins.

Amino Acid Sequence↗
PubMed1974

Purification and characterization of Streptococcus mutans group d cell wall polysaccharide antigen.

The Streptococcus mutans group d antigen of strain B13 has been purified and characterized with respect to chemical composition and immunochemical properties. The antigen was extracted from lyophilized cells or cell walls by using 5% trichloroacetic acid at 5 C for 16 h. The antigen could also be extracted with water or 0.01 N HCl at 100 C for 20 min. The antigen was purified by ion-exchange and gel chromatography and was found to contain 96% carbohydrate, 1.6% protein, and 0.3% phosphorus. Characterization by gas chromatography indicated that the polysaccharide was composed of galactose and glucose in a 2:1 ratio. The antigen contained two serologically active sites: one site specific for group d and a second site common to both group d and group a strains. Agar diffusion and immunoelectrophoresis indicated that the two sites existed on a single molecule. The immunological specificity of the group d polysaccharide site depended on a terminal d-galactose. The purified B13 antigen did not react with antisera specific for the glycerol teichoic acid from streptococci. Anti-d serum rapidly agglutinated whole cells, indicating that the antibody receptor sites of the polysaccharide antigen were at the surface of the streptococcal cell.

Adsorption↗
PubMed1975

Relationship between cell-bound dextransucrase and the agglutination of Streptococcus mutans.

Dextran-induced agglutination of Streptococcus mutans cells is independent of cell-bound dextransucrase activity. Toluene extraction or the presence of Hg2+ or Cu2+ markedly decreased or completely abolished cell-bound dextransucrase activity without adversely affecting dextran-induced cell agglutination. Cells treated by heating at 100 C until cell-bound dextransucrase was completely inactivated continued to agglutinate when induced by dextran-induced cell agglutination resulted from cell treatment with trypsin and several other enzymes, as well as from ethylenediaminetetraacetic acid treatment, without a corresponding loss of cell-bound dextransucrase activity. Cells possessed a greater avidity for branched dextrans of low molecular weight than for linear dextrans of the same weight, indicating that size alone does not determine the efficiency of dextran as an inducer of agglutination. Divalent metal ions were required for both sucrose- and dextran-induced agglutination of S. mutans K1-R cells. Although normal cells of strain 6715-49 did not appear to require divalent cations for agglutination, heat- and ethlyenediaminetetraacetic acid-treated cells specifically required Ca2+. The role of Ca2+ in cell agglutination may be either to activate the cell-surface dextran receptor or to form specific intercellular Ca2+ bridges.

Agglutination↗
PubMed1976

Regulation and extracellular glucosyltransferase production and the relationship between extracellular and cell-associated activities in Streptococcus mutans.

The regulation of extracellular glucosyltransferase production in Streptococcus mutans GS-5 has been studied using a chemically defined medium. Most of the glucosyltransferase activity produced by cells grown in the chemically defined medium was extracellular, in contrast with the distribution between cell-associated and extracellular glucosyltransferase activity when cells were grown in complex medium. The production of extracellular glucosyltransferase activity coincided with the logarithmic growth phase, and further accumulation ceased when glucose was exhausted from the medium. Accumulation of extracellular glucosyltransferase activity was inhibited immediately by chloramphenicol and rifamycin, added either at the beginning of growth or during mid-logarithmic growth. Low concentrations of chloramphenicol inhibited both cellular protein synthesis and the accumulation of extracellular glucosyltransferase activity to the same extent, indicating a close coupling between glucosyltransferase synthesis and secretion. Experiments using cell lysates showed that no intracellular accumulation of glucosyltransferase activity occurred in the presence of the inhibitors and that the intracellular activity is very low relative to the cell-surface activity. The utilization of cells depleted of cell-associated glucosyltransferase activity indicated that most of the cell-associated glucosyltransferase activity does not act as a precursor for the extracellular enzyme. Sugar analogue inhibitors of glycoprotein synthesis did not have any specific effects on the synthesis or secretion of extracellular glucosyltransferase activity.

Bacterial Proteins↗
PubMed1977

Purification, resolution, and interaction of the glucosyltransferases of Streptococcus mutans 6715.

The extracellular glucosyltransferase produced by Streptococcus mutans 6715 was purified from culture supernatant fluids to a specific activity of 9.6 IU/mg of protein, with an overall recovery of 87%. The purified enzyme preparation, designated unfractionated enzyme (UFE), synthesized only water-insoluble glucans from sucrose during the initial stages of the reaction, although some water-soluble polymers accumulated after extended periods of incubation. It was free from measurable fructosyltransferase activity. The UFE preparation was resolved into two different catalytically active components by ethanol fractionation. One fraction (designated insoluble product enzyme [IPE]) synthesized water-insoluble glucans, whereas the other (designated soluble product enzyme [SPE]) produced primarily water-soluble glucans. The difference between the insoluble glucans made by the UFE preparation and those made by the IPE fraction appeared to be due to interaction of the SPE and IPE components in the UFE preparation. Addition of commercial dextrans or enzymatically prepared glucans to the glucosyltransferase assay altered the amounts of soluble and insoluble glucans synthesized by the UFE preparation. The molecular weights of the major enzymatically active proteins producing insoluble and soluble glucans were estimated by gel filtration chromatography to be 150,000 and 175,000, respectively.

Dextranase↗
PubMed1981

Adherence of Streptococcus sanguis clinical isolates to smooth surfaces and interactions of the isolates with Streptococcus mutans glucosyltransferase.

Streptococcus sanguis isolated from human dental plaque were grown in Todd-Hewitt broth. Cells were collected by centrifugation and lyophilized after extensive washing with water. The cell-associated glucosyltransferase (GTase) activities of S. sanguis strains were assayed with [14C]sucrose. Strain differences in GTase activity were significant within the same serotype or biotype or both. The ability of S. sanguis cells to adhere to smooth glass surfaces was generally weak, irrespective of significant cell-associated GTase activity synthesizing water-insoluble, gel-like glucans. Resting cells of most S. sanguis strains bound extracellular GTase from Streptococcus mutans strain B13 (serotype d), resulting in the strong adherence of the S. sanguis cells to smooth glass surfaces in the presence of sucrose. Conversely, S. mutans B13 cells also could bind extracellular GTase from some strains of S. sanguis examined. The sucrose-dependent adherence of S. mutans cells was not altered, although S. sanguis strains from which the extracellular GTases were obtained did not produce significant adherence in the presence of sucrose. In view of these findings, it was suggested that S. mutans GTase could affect the adherence of S. sanguis to smooth tooth surfaces in the oral cavity.

Binding Sites↗
PubMed1982

Physiology of "mutans-like" Streptococcus ferus from wild rats.

Strains of Streptococcus ferus isolated from the oral cavities of wild rodents inhabiting sucrose-rich and sucrose-poor environments have many traits in common with the "mutans" streptococci. Thus, S. ferus HD3 and 8S1, like cariogenic S. sobrinus 6715-13, from adherent, alpha (1 leads to 3) glucopyranosyl-glucose linkage-rich, plaquelike deposits in vitro and in vivo through the action of constitutive glucosyltransferase(s) enzymes on sucrose, produce and degrade intracellular polysaccharide, produce short-chain fatty acids from the catabolism of mono- and disaccharides, carry the c antigen of S. mutans, and penetrate, persist, and proliferate in a sucrose-augmented fashion in the oral cavities of specific-pathogen-free rodent caries models. However, unlike infection with common S. mutans, infection with tested S. ferus strains does not cause caries. This avirulence appeared to result more from the reduced aciduricity of S. ferus than from differences in glucosyltransferase complements. Studies showed that despite generally similar growth rates and extracellular glucan syntheses, the acidogenic metabolism of S. ferus was more inhibited by declining environmental pH than was cariogenic S. sobrinus 6715-13 and that, in vitro, less hydroxyapatite was solubilized by S. ferus metabolic end products. The physiology of these S. ferus strains demonstrated that, in addition to plaque formation and acid production, acid tolerance was crucial to the carious process.

Agglutination↗