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Bernard Kloareg - One of the best experts on this subject based on the ideXlab platform.
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apoplastic oxidation of l asparagine is involved in the control of the green algal endophyte acrochaete operculata correa nielsen by the red seaweed Chondrus Crispus stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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Apoplastic oxidation of L-asparagine is involved in the control of the green algal endophyte Acrochaete operculata Correa & Nielsen by the red seaweed Chondrus Crispus Stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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a signal released by an endophytic attacker acts as a substrate for a rapid defensive reaction of the red alga Chondrus Crispus
ChemBioChem, 2002Co-Authors: Florian Weinberger, Bernard Kloareg, Georg Pohnert, Philippe PotinAbstract:A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus Crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.
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the Chondrus Crispus acrochaete operculata host pathogen association a novel model in glycobiology and applied phycopathology
Journal of Applied Phycology, 2001Co-Authors: Kamal Bouarab, Philippe Potin, Juan A Correa, Florian Weinberger, Bernard KloaregAbstract:A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus Crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. Crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.
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dna sequence structure and phylogenetic relationship of the mitochondrial small subunit rrna from the red alga Chondrus Crispus gigartinales rhodophytes
Journal of Molecular Evolution, 1995Co-Authors: Catherine Leblanc, Bernard Kloareg, Loiseauxde S Goer, Catherine BoyenAbstract:The entire nucleotide sequence containing the small-subunit ribosomal RNA gene (SSU rRNA) from the mitochondrial genome of Chondrus Crispus was determined. To our knowledge, this is the first sequence of a mitochondrial 16S-like rRNA from a red alga. The length of this gene is 1,376 nucleotides. Its secondary structure was constructed and compared with other known secondary structures from eubacteria and from mitochondria of land plants, green and brown algae, and fungi. Phylogenetic trees were built upon SSU rRNA sequence alignment from mitochondria and eubacteria. The results show that rhodophytes and chromophytes provide additional links in the evolution of mitochondria between the green plant lineage and the “nonplant” lineages.
Juan A Correa - One of the best experts on this subject based on the ideXlab platform.
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the Chondrus Crispus acrochaete operculata host pathogen association a novel model in glycobiology and applied phycopathology
Journal of Applied Phycology, 2001Co-Authors: Kamal Bouarab, Philippe Potin, Juan A Correa, Florian Weinberger, Bernard KloaregAbstract:A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus Crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. Crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.
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etiology of infectious diseases in cultivated Chondrus Crispus gigartinales rhodophyta
Hydrobiologia, 1996Co-Authors: James S. Craigie, Juan A CorreaAbstract:The appearance of cavities and holes in fronds of commercially cultivated Chondrus Crispus is described. These ultimately arise from the ravages of a ‘green spot’ or ‘green rot’ disease system in which several biotic agents can participate. Nematodes capable of bacterial grazing were recovered from necrotic lesions and we suggest that the nematodes can facilitate wound healing in diseased tissues. Bacteria isolated from disease lesions and from the surfaces of healthy fronds were screened for pathogenic strains. A particularly virulent one, the DOR isolate, was purified from small dark orange colored colonies grown on dilution plates. It was present in necrotic tissue and also recovered from surface scrapings of old healthy fronds, but not from their apical regions. Growth of the DOR isolate appeared to be inhibited by other bacteria colonizing the algal surface. It was shown to be a facultative pathogen, the virulence of which depended on the availability of ammonium or constituents easily metabolized to ammonium. It induced green rot disease in healthy C. Crispus and was recoverable in pathogenic form from experimentally infected frond apices. A wound, disease and recovery cycle is discussed to illustrate potential interrelationships involving animal grazers, algal endophytes, Petersenia pollagaster, bacteria and nematodes.
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endophytic algae of Chondrus Crispus rhodophyta v fine structure of the infection by acrochaete operculata chlorophyta
European Journal of Phycology, 1994Co-Authors: Juan A Correa, Jack MclachlanAbstract:The sequence of events taking place during infection of the algal host Chondrus Crispus by the algal endophyte Acrochaete operculata was characterised at the ultrastructural level. Infection required settlement of quadriflagellate zoospores on the outer cell wall of the host. The host outer cell wall did not represent a barrier against penetration by the endophyte, which digested its way through. The extent of further spread of A. operculata in C. Crispus was determined by the life-history phase of the host. In sporophytic fronds, colonisation of inner tissues occurred by digestion of the intercellular matrix, and infection spread throughout the frond. In gametophytic thalli, infection remained localised, forming a characteristic papule. In spite of these differences, degenerative changes at the cellular level were similar in the two phases of the host. Damage was caused by compression and by penetration of host cells. Final breakdown of the host resulted from the combined effects of A. operculata and bac...
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cuticles from Chondrus Crispus rhodophyta 1
Journal of Phycology, 1992Co-Authors: James S. Craigie, Juan A Correa, Margaret E GordonAbstract:A simple, nondestructive physical process was developed for routinely isolating the outermost layers from female, male, and sporophyte fronds of Chondrus Crispus Stack-house. Yields of pure cuticles from apical segments ranged from 0.74 to 2.35% on a dry weight basis after 5–7 d of culture. These undegraded cuticles were examined by electron microscopy (scanning and transmission electron microscopy), spectroscopy (infrared and X-ray), and chemical means. Cuticles isolated from female or male fronds were characterized by parallel arrays of electron-dense lamellae (typically 6–14) alternating with more electron-transparent regions. The thickness and uniformity of these lamellae provide the physical basis for the iridescence characteristic of C. Crispus fronds. Sporophyte fronds are not iridescent. This phenomenon may be explained by the fewer electron-dense cuticular lamellae (usually three to seven) and the fact that these lamellae anastomose freely to form a thin cuticle with a highly irregular substructure. Elements detected by X-ray analysis, in addition to carbon and oxygen, included Mg, Br, S, and Ca in both gametophyte and sporophyte cuticles. Major features of FTIR spectra of all cuticles were absorbances due to proteins. A strong band, indicative of sulfate ester, occurred near 1250 cm−1 in all cuticle preparations. Gametophyte, but not sporophyte, cuticles absorbed at 935, 846, and 800 cm−1 consistent with the presence of kappa and/or iota carrageenan. Amino acid analyses showed that sporophyte and gametophyte cuticles were generally similar in gross composition. All contained proline as the principal residue together with significant amounts of cysteine, methionine, and lysine. Protein contents calculated from these analyses ranged from 37.6 to 44.4% on a dry weight basis as compared to 51.5–56.7% calculated from total nitrogen values. Up to 75% of the cuticle mass was solubilized by sodium dodecyl sulfate-β-mercaptoethanol. Three similar migrating bands were seen in female and male cuticle extracts on sodium dodecyl sulfate–polyacrylamide gel electrophoresis; however, none of the three weaker bands from sporophyte cuticles comigrated with those from gametophytes. Chloroform-methanol extraction removed < 3.3% of the cuticle mass, suggesting that lipids were minor components.
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endophytic algae of Chondrus Crispus rhodophyta iii host specificity1
Journal of Phycology, 1991Co-Authors: Juan A Correa, J MclachlanAbstract:Susceptibility of rhodophycean macroalgae to infection by the green endophytes, Acrochaete operculata Correa & Nielsen and A. heteroclada Correct & Nielsen was studied. Cross-infection experiments showed that A. operculata is host specific and developed only in sporophytic fronds of Chondrus Crispus Stackh. and Iridaea cordata (Turn.) Bory. Although A. operculata penetrated equally the multilamellar outer cell wall of sporophytic and gametophytic fronds of C. Crispus, subsequent development was arrested in the gametophytic fronds. Susceptibility of the sporophytic phase of C. Crispus was detected early in the development of the host, at a discoid stage that is structurally distinct from the adult fronds. The evidence strongly suggests that host specificity in A. operculata is determined by cell-wall composition of the hosts, likely the carrageenan fraction. In contrast, A. heteroclada was not host specific, infecting all offered hosts, including carrageenophytes and agarophytes. Germination occurred on the surface of the hosts and led to the development of an epiphytic stage. Subsequent penetration in many cases involved total displacement of cortical tissue in the infected frond.
Philippe Potin - One of the best experts on this subject based on the ideXlab platform.
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Chondrus Crispus – A Present and Historical Model Organism for Red Seaweeds
Advances in Botanical Research, 2020Co-Authors: Jonas Collen, James S. Craigie, Cecile Herve, Catherine Leblanc, M. Lynn Cornish, Elizabeth Ficko-blean, Stacy A. Krueger-hadfield, Gurvan Michel, Philippe Potin, Thierry TononAbstract:Abstract Chondrus Crispus, or Irish moss, is a common edible red seaweed that can be found on rocky shores in the Northern Atlantic. The cell wall contains carrageenan and C. Crispus is the original source of this commercially used thickener. Because of the ecological and economic importance of this red alga a relatively important research literature exists and one of the recent achievements in C. Crispus research is the sequencing of its genome. In this chapter we review some of the literature with the aim to promote C. Crispus as a model organism for florideophyte red seaweeds. We consider subjects like commercial and historical uses, ecology, genetics, population structure, mating systems, physiology, cell wall biology and genomics.
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apoplastic oxidation of l asparagine is involved in the control of the green algal endophyte acrochaete operculata correa nielsen by the red seaweed Chondrus Crispus stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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Apoplastic oxidation of L-asparagine is involved in the control of the green algal endophyte Acrochaete operculata Correa & Nielsen by the red seaweed Chondrus Crispus Stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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a signal released by an endophytic attacker acts as a substrate for a rapid defensive reaction of the red alga Chondrus Crispus
ChemBioChem, 2002Co-Authors: Florian Weinberger, Bernard Kloareg, Georg Pohnert, Philippe PotinAbstract:A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus Crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.
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the Chondrus Crispus acrochaete operculata host pathogen association a novel model in glycobiology and applied phycopathology
Journal of Applied Phycology, 2001Co-Authors: Kamal Bouarab, Philippe Potin, Juan A Correa, Florian Weinberger, Bernard KloaregAbstract:A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus Crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. Crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.
J Mclachlan - One of the best experts on this subject based on the ideXlab platform.
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reproductive ecology of Chondrus Crispus rhodophyta gigartinales from nova scotia canada
Botanica Marina, 1994Co-Authors: Ricardo A Scrosati, David J Garbary, J MclachlanAbstract:Spore production and viability were studied in Chondrus Crispus based on monthly samples from June to October 1991 at Tor Bay on the Atlantic coast of Nova Scotia. Random collection of fronds showed a gametophyte: tetrasporophyte ratio of about 3: 1. Two reproductive periods were distinguished based on number and diameter of cystocarps and number of tetrasporic sori g −1 frond weight, with reproductive fronds in June and July having larger and fewer cystocarps, and fewer tetrasporic sori g −1 than fronds collected from August to October. The pattern of daily spore release was variable among months. Spore viability varied between monthly means of 4-16% for carpospores and 6-26% for tetraspores, with maximum viability in June and August for carpospores and tetraspores, respectively
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endophytic algae of Chondrus Crispus rhodophyta iii host specificity1
Journal of Phycology, 1991Co-Authors: Juan A Correa, J MclachlanAbstract:Susceptibility of rhodophycean macroalgae to infection by the green endophytes, Acrochaete operculata Correa & Nielsen and A. heteroclada Correct & Nielsen was studied. Cross-infection experiments showed that A. operculata is host specific and developed only in sporophytic fronds of Chondrus Crispus Stackh. and Iridaea cordata (Turn.) Bory. Although A. operculata penetrated equally the multilamellar outer cell wall of sporophytic and gametophytic fronds of C. Crispus, subsequent development was arrested in the gametophytic fronds. Susceptibility of the sporophytic phase of C. Crispus was detected early in the development of the host, at a discoid stage that is structurally distinct from the adult fronds. The evidence strongly suggests that host specificity in A. operculata is determined by cell-wall composition of the hosts, likely the carrageenan fraction. In contrast, A. heteroclada was not host specific, infecting all offered hosts, including carrageenophytes and agarophytes. Germination occurred on the surface of the hosts and led to the development of an epiphytic stage. Subsequent penetration in many cases involved total displacement of cortical tissue in the infected frond.
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Relationship between cover of Chondrus Crispus (Gigartinales, Rhodophyta) and Phymatolithon (Corallinales, Rhodophyta) on friable rock substrata
Hydrobiologia, 1990Co-Authors: Terry Parker, J MclachlanAbstract:Field observations in sublittoral Prince Edward Island, Canada, indicated that on a friable sandstone substratum Chondrus Crispus was more commonly associated with Phymatolithon sp. than with bare rock. Thus, a substantial proportion of the population of Irish moss along the coast of Prince Edward Island occurs on this encrusting coralline. These observation may be explained on the basis of the relative stability of the substratum in contrast to other studies in which sloughing of epithallial cells by species of both Phymatolithon and Lithothamnium has been reported to limit epiphytism by fleshy macrophytes.
Florian Weinberger - One of the best experts on this subject based on the ideXlab platform.
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apoplastic oxidation of l asparagine is involved in the control of the green algal endophyte acrochaete operculata correa nielsen by the red seaweed Chondrus Crispus stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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Apoplastic oxidation of L-asparagine is involved in the control of the green algal endophyte Acrochaete operculata Correa & Nielsen by the red seaweed Chondrus Crispus Stackhouse
Journal of Experimental Botany, 2005Co-Authors: Florian Weinberger, Kamal Bouarab, Bernard Kloareg, Georg Pohnert, Marylynn Berndt, Philippe PotinAbstract:Gametophytes of the marine alga Chondrus Crispus are more resistant than tetrasporophytes to infection by the filamentous endophytic alga Acrochaete operculata. It has been shown recently that carrageenan oligosaccharides from the resistant gametophytic generation of C. Crispus stimulate the secretion of L-asparagine (L-Asn) by the endophyte and that the host generates hydrogen peroxide and 2-oxo-succinamic acid after contact with this amino acid. Here the response of C. Crispus to L-Asn and its effect on the pathogen is investigated. Chondrus Crispus released hydrogen peroxide, ammonium ions, and a carbonyl compound into the medium when exposed to L-Asn. This response was correlated with an increase in oxygen consumption. Inhibitor studies indicated the involvement of a flavoenzyme in the reaction, which was sensitive to high concentrations of the reaction product, ammonium, and to chlorpromazine, quinacrine, and cyanide, inhibitors of L-amino acid oxidase. Cell wall macerate of C. Crispus also responded to L-Asn, while protoplasts were inactive. Uptake of L-Asn into the cell was not necessary for the response, suggesting that the involved L-amino acid oxidase is apoplastic. Acrochaete operculata was more sensitive to hydrogen peroxide than C. Crispus and settlement of A. operculata zoospores on C. Crispus was reduced by 86% in the presence of L-Asn. This reduced settlement could be prevented with catalase. Chondrus Crispus thus features an apoplastic amino acid oxidase, which is involved in the control of its endophytic pathogen. The modulation of the amino acid secretion in A. operculata by carrageenan oligosaccharides is therefore a key issue in the etiology of the association.
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a signal released by an endophytic attacker acts as a substrate for a rapid defensive reaction of the red alga Chondrus Crispus
ChemBioChem, 2002Co-Authors: Florian Weinberger, Bernard Kloareg, Georg Pohnert, Philippe PotinAbstract:A backfiring weapon: The release of H2O2 by an amino acid oxidase is the early defensive reaction of the red alga Chondrus Crispus against the endophytic green algal pathogen Acrochaete operculata (see scheme). This reaction can be induced by L-asparagine, which is released by the attacker when it recognises host cell-wall κ-carrageenan oligosaccharides. The induced signal of the attacker thus serves directly as the substrate for the production of the defensive metabolite.
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the Chondrus Crispus acrochaete operculata host pathogen association a novel model in glycobiology and applied phycopathology
Journal of Applied Phycology, 2001Co-Authors: Kamal Bouarab, Philippe Potin, Juan A Correa, Florian Weinberger, Bernard KloaregAbstract:A review is presented of ongoing research on the oligosaccharide signals involved in cell-cell recognition in the Chondrus Crispus-Acrochaete operculata host-pathogen association. In this pathosystem, the host gametophytes are resistant to the pathogen, whereas the sporophytic generation is susceptible to infection. The virulence of the green algal pathogen is mediated by the recognition of carrageenan oligosaccharides released from its red algal host: kappa-carrageenan oligosaccharides inhibit A. operculata virulence while lambda carrageenan oligosaccharides enhance its pathogenicity. It appears that the recognition of A. operculata by C. Crispus also involves an oligosaccharidic signal. This signal is present in the non-virulent form of the pathogen whereas it is absent from the virulent form. Altogether this pathosystem offers a unique model to investigate the recognition of oligosaccharide signals in plant-pathogen interactions. The possible applications of this research to develop new strategies for disease control in maricultured algal crops are discussed.