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Musa --- Mycosphaerella fijiensis --- Host pathogen relations --- Molecular biology --- 634.771 --- 632.4 --- 632.4 Algal and fungal diseases of plants. Plant mycoses etc. --- Algal and fungal diseases of plants. Plant mycoses etc. --- 634.771 Musa species in general --- Musa species in general

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Zea mays --- Maladie fongique --- Fungal diseases --- Toxine --- Toxins --- Agent pathogène --- Pathogens --- Perte après récolte --- Postharvest losses --- Physiologie après récolte --- Postharvest physiology --- Développement biologique --- biological development --- 631.56 --- 633.15 --- 632.4 --- Preparation of produce. Treatment after harvesting. Postharvest --- Maizes. Indian corns. Zea mays. Sweet corn --- Algal and fungal diseases of plants. Plant mycoses etc. --- Theses --- Sciences and engineering --- biological sciences --- agriculture --- food science and technology --- 632.4 Algal and fungal diseases of plants. Plant mycoses etc. --- 633.15 Maizes. Indian corns. Zea mays. Sweet corn --- 631.56 Preparation of produce. Treatment after harvesting. Postharvest --- food science and technology. --- Lutte --- Biological sciences --- Agriculture --- Food science and technology.

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632.4 --- 633.496 --- Algal and fungal diseases of plants. Plant mycoses etc. --- Yautia, tannia or coco-yam. Xanthosoma --- Theses --- Sciences and engineering --- biological sciences --- biology --- microbiology --- agriculture --- plant pathology --- 633.496 Yautia, tannia or coco-yam. Xanthosoma --- 632.4 Algal and fungal diseases of plants. Plant mycoses etc. --- microbiology. --- plant pathology. --- Xanthosoma sagittifolium --- Diseases and pests --- Cameroon --- Root crops --- Pythium myriotylum --- Biological control --- Phytopathogenic fungi --- Agricultural pests --- Xanthosoma sagittifolium root rot --- Biological sciences --- Agriculture --- Plant pathology. --- Biology --- Microbiology.

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De doelstelling van dit onderzoek was de verdere ontrafeling van het antifungaal werkingsmechanisme van plantdefensinen. Plantdefensinen zijn kleine, basische, cysteine-rijke componenten die actief zijn tegen verschillende plantpathogene schimmels alsook schimmelpathogenen van de mens, maar niet toxisch zijn voor planten- of menselijke cellen. Eerder werd aangetoond dat plantdefensinen de groei van de schimmelcel inhiberen door de schimmelmembraan te permeabilizeren na interactie met specifieke bindingsplaatsen op de schimmelmembraan. Voor het defensine DmAMP1 uit dahlia en het defensine RsAFP2 uit radijs werden deze bindingplaatsen geïdentificeerd als sfingolipiden. Sfingolipiden zijn bouwstenen van eukaryotische membranen, maar treden ook op als signaalmoleculen in verschillende cellulaire processen. In dit onderzoek konden we aantonen dat RsAFP2 sfingolipiden-bevattende lipidenvesikels niet kan permeabilizeren wat de hypothese van schimmelmembraan-permeabilisatie door directe insertie in de membraan van plantdefensinen na hun interactie met de sfingolipiden onwaarschijnlijk maakt. We toonden daarentegen een oorzakelijk verband aan tussen de productie van reactieve zuurstofspecies (ROS) geïnduceerd door RsAFP2 en zijn antifungale activiteit. Bovendien konden we bewijs leveren voor de inductie van geprogrammeerde celdood (apoptose) door RsAFP2 in gevoelige schimmels. Deze data suggereren dat RsAFP2 een intracellulaire signaalcascade activeert die verder leidt tot schimmelgroei-inhibitie. Een algemene techniek voor het ontrafelen van het werkingsmechanisme van antifungale componenten en de verdedigingsmechanismen van de schimmel tegen deze componenten is de screening van Saccharomyces cerevisiae mutantenbanken en het uitvoeren van aanvullende biochemische testen. In dit onderzoek werd zulke screening toegepast voor DmAMP1 en het defensine HsAFP1 uit purperklokje. Deze techniek is echter niet toepasbaar voor RsAFP2 aangezien S. cerevisiae intrinsiek resistent is aan RsAFP2. Op deze manier konden we in preliminaire testen aantonen dat HsAFP1 ROS en apoptose induceert in gevoelige schimmels. Ook toonden we het belang aan van mitochondriale respiratie en van het actine-cytoskelet in de antifungale activiteit van HsAFP1. Verder werd duidelijk dat schimmels verschillende stress-respons-signaalwegen gebruiken als verdedigingsmechanisme tegen HsAFP1. Tot slot konden we de cruciale rol van het sfingolipide M(IP)2C in het antifungale werkingsmechanisme van DmAMP1 bevestigen. Door de karakterisiatie van gistmutanten met een veranderd plantdefensine gevoeligheidsfenotype en met een veranderd sfingolipidenprofiel konden we ook fundamentele sfingolipiden-gemedieerde processen ontrafelen. Zo toonden we aan dat hoge M(IP)2C hoeveelheden in gist resulteren in verhoogde gevoeligheid aan oxidatieve stress en een korte chronologische levensduur. Daarnaast konden we een verband bepalen tussen modulatie van sfingolipiden (overexpressie van een ceramidase) en de morfologie van organellen met gevolgen voor apoptose en chronologische levensduur. Tot slot toonden we aan dat twee structureel homologe peptiden uit verschillende eukaryotische rijken (plantdefensinen en humane defensinen) ook functioneel homoloog zijn. Arabidopsis thaliana planten die het humaan β-defensine 2 heteroloog tot expressie brengen, bleken namelijk meer resistent te zijn tegen infectie door de schimmel Botrytis cinerea. Gebaseerd op de fundamentele onderzoeksresultaten van deze thesis, worden mogelijke toepassingen van defensinen in de landbouw en geneeskunde besproken. The aim of this doctoral study was to further unravel the mode of antifungal action of plant defensins. Plant defensins are small, cationic, cysteine-rich components that are active against different phytopathogenic fungi and human pathogens, but are not toxic to human and plant cells. It was previously shown that plant defensins induce membrane permeabilization and inhibit fungal cell growth through interaction with specific binding sites in the fungal cell membrane. For the dahlia defensin DmAMP1 and the radish defensin RsAFP2, these binding sites were identified as sphingolipids. Sphingolipids are building blocks of eukaryotic membranes, but are also important signalling molecules in different cellular processes. In this study, we demonstrated that RsAFP2 is not able to permeabilize sphingolipid-containing vesicles, making the hypothesis of fungal membrane permeabilization by direct insertion of this plant defensin in the membrane after their interaction with sphingolipids unlikely. Instead, we demonstrated a causal link between RsAFP2-induced reactive oxygen species (ROS) generation and its antifungal action. Moreover, evidence was provided for the induction of apoptosis by RsAFP2 in susceptible fungi/yeast. These findings point to the presence of an intracellular RsAFP2-induced signalling cascade, leading to fungal cell growth arrest. A general technique to unravel the mode of antifungal action of antifungal compounds and the yeast tolerance mechanisms towards these antifungal compounds is the screening of Saccharomyces cerevisiae mutant libraries for mutants with altered sensitivity towards these compounds and the performance of additional biochemical tests. In this study, this technique was used for the defensin HsAFP1 from coral bells and DmAMP1, but not for RsAFP2 since S. cerevisiae is intrinsically resistant to RsAFP2. In this way, we demonstrated that HsAFP1 is probably involved in the induction of apoptosis in susceptible fungi. Moreover, we demonstrated the importance of mitochondrial respiration and the actin cytoskeleton for HsAFP1 antifungal activity. Furthermore, we demonstrated the role of various stress response signalling pathways in mediating HsAFP1 tolerance in yeast. Finally, we confirmed the crucial role of the sphingolipid M(IP)2C in DmAMP1 antifungal action. By characterization of yeast mutants with an altered plant defensin sensitivity and an altered sphingolipid profile, we unravelled fundamental sphingolipid-mediated processes. Indeed, we showed that high M(IP)2C levels in yeast result in increased sensitivity towards oxidative stress and a short chronological lifespan. Furthermore, we demonstrated a link between modulation of sphingolipid levels (overexpression of a ceramidase) and organelle morphology with consequences for apoptosis and chronological lifespan. Finally, we demonstrated that two structurally homologous peptides from different eukaryotic kingdoms (plant defensins and human β-defensins) are also functionally homologous. Indeed, we showed that Arabidopsis thaliana plants heterologously expressing human β-defensin 2 are more resistant to fungal infection by Botrytis cinerea. Based on the fundamental research results of this thesis, potential applications of defensins in agriculture and medicine are discussed.

Academic collection --- 577.27 --- 579 --- 632.938 --- 632.4 --- 632.4 Algal and fungal diseases of plants. Plant mycoses etc. --- Algal and fungal diseases of plants. Plant mycoses etc. --- 632.938 Immunology. Plants resistant to diseases and pests. Immunization of plants --- Immunology. Plants resistant to diseases and pests. Immunization of plants --- 579 Microbiology --- Microbiology --- 577.27 Molecular bases of immunity. Molecular immunology --- Molecular bases of immunity. Molecular immunology --- Theses

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Blight [Rice sheath ] --- Champignons phytopathogènes --- Fungal diseases of plants --- Fytopathogene zwammen --- Lactoflavin --- Maladies fongiques des plantes --- Phytopathogenic fungi --- Plant fungi --- Rhizoctonia solani --- Riboflavin --- Rice sheath blight --- Schimmelziekten van de planten --- Sheath blight disease of rice --- Stem and crown blight of rice --- Vitamin B2 --- Vitamin G --- Zwammen [Fytopathogene ] --- Oryza --- Marqueur génétique --- genetic markers --- diagnosis --- Riboflavine --- Résistance induite --- Induced resistance --- Réponse de la plante --- Plant response --- Lignine --- Lignins --- Oxydoréduction --- Oxidoreductions --- 633.18 --- 632.4 --- 582.288.4 --- Rices. Oryza --- Algal and fungal diseases of plants. Plant mycoses etc. --- Hyphomycetes. Penicillium. Verticillium. Helminthosporium. Botrytis. Moniliella. Aspergillus. Rhizoctonia. Trichoderma --- Theses --- 582.288.4 Hyphomycetes. Penicillium. Verticillium. Helminthosporium. Botrytis. Moniliella. Aspergillus. Rhizoctonia. Trichoderma --- 632.4 Algal and fungal diseases of plants. Plant mycoses etc. --- 633.18 Rices. Oryza --- Rice --- Diseases and pests