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Dissertation
Acquired resistance to systemic fungicides of Septoria nodorum and Cercosporella herpotrichoides in cereals
Authors: --- ---
Year: 1979 Publisher: Wageningen Landbouwhogeschool,


Dissertation
Modelluntersuchungen zur Resistenz von Gerstenmehltau (Erysiphe graminis f.sp. hordei Marchal) gegenüber systemischen Fungiziden


Dissertation
Untersuchungen über die Mikroverteilung von Schutzsalzen auf Kupfer-Chrom-Arsen-Basis in Laubhölzern und ihre Wirksamkeit gegenüber Moderfäulepilzen
Authors: ---
Year: 1978 Publisher: Hamburg Universität Hamburg,


Dissertation
Monosomen-Analyse der Resistenz gegenüber Gelbrost (Puccinia striiformis West.) beim Weizen, Triticum aestivum L.


Dissertation
Untersuchungen zum Nachweis und Besiedlungsverhalten sowie zur Bekämpfung der Erreger der Triebsucht des Apfels und des Birnenverfalls


Multi
Cylindrocladium buxicola nom. cons. prop. (syn. Calonectria pseudonaviculata) on Buxus : molecular characterization, epidemiology, host resistance and fungicide control
Authors: ---
ISBN: 9789059896963 Year: 2014 Publisher: Gent Universiteit Gent. Faculteit Bio-Ingenieurswetenschappen


Dissertation
Functional analysis of the trehalose metabolism gene family in Arabidopsis thaliana.

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Abstract

Trehalose heeft een belangrijke rol als reserve koolhydraat en stress-beschermer in een groot aantal verschillende organismen. Dit suiker wordt hoofdzakelijk aangemaakt met behulp van twee enzymes, trehalose-6-fosfaat (T6P)-synthase (TPS) en T6P-fosfatase (TPP). Lange tijd werd aangenomen dat trehalose synthese afwezig zou zijn in hoger geëvolueerde planten, niettegenstaande trehalose in grote hoeveelheden opgestapeld wordt in sommige lagere planten in droogte-stress. Heterologe expressie van microbiële trehalose biosynthese genen veroorzaakte echter dramatische veranderingen in groei, ontwikkeling, metabolisme, en stress resistentie in hogere planten, wat wijst op een belangrijke regulatorische functie. Meer nog, hogere planten blijken een hele familie van trehalose biosynthese orthologen te bevatten, wat suggereert dat de synthese van dit suiker in planten lang niet zo uitzonderlijk is als voordien verondersteld werd. In dit werk werden de 21 genen van de model plant Arabidopsis thaliana, die vermoedelijke coderen voor trehalose biosynthese enzymen, getest in een groei- complementatie proef in gistcellen. Hierbij bleek van de klasse I TPS proteïnen enkel AtTPS1 de groei van een gist tps1 mutant op glucose te herstellen, conform eerdere gerapporteerde TPS activiteitsmetingen voor dit enzyme. In tegenstelling tot de klasse II TPS homologen die de groei van de gist mutanten niet konden complementeren (duidend op niet-significant TPS/TPP activiteit), hadden de klasse III TPP proteïnen allen duidelijk TPP activiteit, met welliswaar verschillende kinetische eigenschappen. De aanwezigheid van T6P binding plaatsen in de klasse II TPS proteïnen, duidt eerder op een functie als T6P sensoren dan als katalytisch actieve enzymen. In tegenstelling tot de robuuste regulatie door suiker- en licht behandelingen van de klasse II TPS genen, blijken de klasse III TPP genen veleer minder sterk gereguleerd door deze behandelingen. Echter, een gedetaileerde studie van de expressie van de 10 verschillende TPP genen, wijst op een opmerkelijk divers expressiepatroon voor elke gen in ruimte en tijd. Meer nog, sommige TPP genen vertonen zeer verfijnde expressies in specifieke cellen of in een bepaalde ontwikkelingsfase. Deze resultaten zijn consistent met de belangrijke regulatorisch functies van, en de noodzaak aan een strakke controle over, de hoeveelheid T6P, wetende dat de klasse III TPP genen coderen voor actieve TPP proteïnen. Meer nog, T6P komt steeds vaker naar voor als een nieuwe groeiregulator, die de koolstof voorziening koppelt aan de groei, de ontwikkeling en de stress resistentie van planten. Verder werd er aandacht geschonken aan één klasse II TPS gen (AtTPS5), één klasse III TPP gen (AtTPPG), en AtTRE1, het enige trehalase gen gekend in Arabidopsis. Het afzonderlijk deleteren van deze genen veroorzaakte onder normale groei-omstandigheden geen grote fenotypische veranderingen in Arabidopsis. Afhankelijke van het licht regime, werden echter wel gewijzigde bladontwikkeling en bloei-inductie waargenomen bij de AtTPS5 en AtTRE1 gedeleteerde planten en AtTPPG mutatie gaf aanleiding tot een gemodificeerd zetmeel metabolisme. Meer nog, trehalase blijkt een belangrijke rol te spelen in de reactie van planten op stress. Alle 3 de genen zijn ook, welliswaar in verschillende mate, betrokken bij het optimale gebruik van koolhydraten, werkzaam in de coördinatie van de groei van de plant met de energie voorziening. Heel interesant hierbij is dat de welgekende energie sensor, SnRK1, zowel AtTPS5 als AtTPPG blijkt te reguleren, zowel op transcriptioneel als op translationeel niveau. Proteïne-proteïne interactie-studies, uitgevoerd om meer directe functies te vinden voor zowel AtTPS5 als AtTPPG, toonden ons een hele resem van verschillende enzymen als potentiële interagerende proteïnen. Deze enzymen zijn betrokken in verschillende uiteenlopende processen in de plant: van metabolisme, signalering tot ontwikkeling. Dit wijst erop dat trehalose metabolisme mogelijks betrokken is, en een significante betekenis kan hebben, in alle facetten van een plantenleven. Tot slot zijn we dieper ingegaan op de functie van suiker en energie signalering in biotische stress reacties in hogere planten. Hiervoor hebben we gebruik gemaakt van een specifiek plant-pathogeen pathosystem, met de obligaat biotroof Plasmodiophora brassicae en de model plant Arabidopsis. We hebben hierbij duidelijke indicaties gevonden dat SnRK1 activiteit de reactie van de plant in infectie sterk beïnvloedt. Niettegenstaande we het exact werkingsmechanisme nog aan het ontrafelen zijn, blijkt de globale inductie van een ‘energie besparend programma’ door SnRK1 activiteit de incentieven van de pathogeen tegen te werken. De pathogeen wil namelijk het endogeen plant koolstof metabolisme misleiden en gebruiken in zijn voordeel. Kennis van de exacte moleculaire mechanismen achter plant trehalose metabolisme en SnRK sigalering zal ons mogelijk maken in de nabije toekomst om belangrijke landbouwgewassen te verbeteren naar een hogere kwaliteit en opbrengst. Trehalose functions as a major reserve sugar and stress protectant in a large variety of organisms. The major pathway for trehalose synthesis involves a trehalose-6-phosphate (T6P)-synthase (TPS) and a T6P-phosphatase (TPP). With the exception of some lower stress-tolerant plant organisms, trehalose synthesis has long been thought to be absent in higher plants. However, its presence and significance began to dawn when ectopic expression of microbial trehalose metabolism genes were found to result in dramatic phenotypes, affecting plant sugar partitioning, growth, development and stress resistance. Moreover, higher plants seem to encode a remarkably large family of putative trehalose biosynthesis enzymes. In this study, we have analysed the 21 putative trehalose biosynthesis proteins of the model plant Arabidopsis thaliana in yeast growth complementation assays. From class I TPS proteins, only AtTPS1 showed explicit TPS activity. For all 7 class II TPS proteins, neither significant TPS nor TPP activity could be observed. The 10 class III TPP proteins, however, all displayed TPP activity, but with different kinetics. Given the observed conservation of T6P binding residues, the class II TPS proteins might operate as T6P sensors, rather than catalytically active enzymes. In contrast to the rigorous differential sugar- and light regulation of class II TPS gene expression, class III TPP gene expression seems less extensively regulated by these treatments. However, in-depth gene expression analysis with promoter-GUS/GFP reporter lines for all class III TPP genes, did reveal remarkably specific spatio-temporal expression patterns; for some TPPs even limited to particular cell types or developmental stages. Given that the class III TPP genes are encoding active TPP enzymes, these results are consistent with the need for a rigid level control of and important regulatory functions for T6P, which is emerging as a novel growth regulator coordinating carbon supply with plant growth, development and stress resistance. We have then characterized in more detail one class II TPS gene (AtTPS5), one class III TPP gene (AtTPPG), and the only known trehalase gene in Arabidopsis, AtTRE1. In general, the phenotypes of the single null mutants largely resembled wild type under normal growth conditions. Depending on the light regime, however, AtTPS5 knock-out (KO) and AtTRE1 KO mutants displayed altered leaf development and flower time, and AtTPPG KO mutants exhibit altered starch levels. Moreover, trehalase seems to play a role in plant stress responses. Remarkably, all three the genes seem to a different extent important for the optimal utilization of carbohydrates, possibly mediating the coordination of growth with the available energy. Furthermore, the energy sensor SnRK1 appears to regulate AtTPS5 and AtTPPG both transcriptionally and translationally. Moreover, protein-protein interaction studies revealed that both proteins are interacting with multiple plant metabolic and signaling pathways, and developmental processes, indicating that trehalose metabolism is strongly integrated in the entire plant life. Finally, we also addressed the role of sugar and energy signaling in biotic stress responses. Using a specific plant-pathogen system with the obligate biotroph Plasmodiophora brassiceae, we observed that SnRK1 activity strongly affects plant performance during biotic stress. Although we are still in the process of unraveling the mechanism involved, we propose that the global induction of a ‘energy saving program’ by SnRK1 counters the incentives of the pathogen to mislead and use endogenous plant carbon metabolism for its own benefit. Knowledge of the exact molecular mechanisms mediating the plant’s use of trehalose metabolism and SnRK signaling will eventually enable us to engineer crops with superior yield and quality. interagerende proteïnen. Deze enzymen zijn betrokken in verschillende uiteenlopende processen in de plant: van metabolisme, signalering tot ontwikkeling. Dit wijst erop dat trehalose metabolisme mogelijks betrokken is, en een significante betekenis kan hebben, in alle facetten van een plantenleven. Tot slot zijn we dieper ingegaan op de functie van suiker en energie signalering in biotische stress reacties in hogere planten. Hiervoor hebben we gebruik gemaakt van een specifiek plant-pathogeen pathosystem, met de obligaat biotroof Plasmodiophora brassicae en de model plant Arabidopsis. We hebben hierbij duidelijke indicaties gevonden dat SnRK1 activiteit de reactie van de plant in infectie sterk beïnvloedt. Niettegenstaande we het exact werkingsmechanisme nog aan het ontrafelen zijn, blijkt de globale inductie van een ‘energie besparend programma’ door SnRK1 activiteit de incentieven van de pathogeen tegen te werken. De pathogeen wil namelijk het endogeen plant koolstof metabolisme misleiden en gebruiken in zijn voordeel. Kennis van de exacte moleculaire mechanismen achter plant trehalose metabolisme en SnRK sigalering zal ons mogelijk maken in de nabije toekomst om belangrijke landbouwgewassen te verbeteren naar een hogere kwaliteit en opbrengst. for T6P, which is emerging as a novel growth regulator coordinating carbon supply with plant growth, development and stress resistance. We have then characterized in more detail one class II TPS gene (AtTPS5), one class III TPP gene (AtTPPG), and the only known trehalase gene in Arabidopsis, AtTRE1. In general, the phenotypes of the single null mutants largely resembled wild type under normal growth conditions. Depending on the light regime, however, AtTPS5 knock-out (KO) and AtTRE1 KO mutants displayed altered leaf development and flower time, and AtTPPG KO mutants exhibit altered starch levels. Moreover, trehalase seems to play a role in plant stress responses. Remarkably, all three the genes seem to a different extent important for the optimal utilization of carbohydrates, possibly mediating the coordination of growth with the available energy. Furthermore, the energy sensor SnRK1 appears to regulate AtTPS5 and AtTPPG both transcriptionally and translationally. Moreover, protein-protein interaction studies revealed that both proteins are interacting with multiple plant metabolic and signaling pathways, and developmental processes, indicating that trehalose metabolism is strongly integrated in the entire plant life. Finally, we also addressed the role of sugar and energy signaling in biotic stress responses. Using a specific plant-pathogen system with the obligate biotroph Plasmodiophora brassiceae, we observed that SnRK1 activity strongly affects plant performance during biotic stress. Although we are still in the process of unraveling the mechanism involved, we propose that the global induction of a ‘energy saving program’ by SnRK1 counters the incentives of the pathogen to mislead and use endogenous plant carbon metabolism for its own benefit. Knowledge of the exact molecular mechanisms mediating the plant’s use of trehalose metabolism and SnRK signaling will eventually enable us to engineer crops with superior yield and quality.


Dissertation
Gewasbescherming m.b.v. Bacillus thuringiensis : commerciële haalbaarheid van ingebouwde resistentie tegen rupsen bij de teelt van tomaten en koolgewassen in Turkije en Thaïland.

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Multi
Bacterial leaf endophytes in African Rubiaceae
Authors: ---
ISBN: 9789086496785 Year: 2013 Publisher: Leuven Katholieke Universiteit Leuven

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Thesis objectivesThe main objective of this thesis was to study the diversity and evolution of bacterial leaf endophytes in African Rubiaceae. Endophytic bacteria were found in six rubiaceous species that cause gousiekte in South Africa: two species of the tribe Pavetteae have nodulated endophytes and four species of the Vanguerieae tribe have non-nodulated endophytes. This second type of endosymbiosis was not studied before. Firstly, a phylogenetic and taxonomic study of Vanguerieae had to be carried out before the evolution of bacterial leaf symbiosis could be studied. Secondly, the bacterial endophytes in the gousiekte-inducing species were identified. Thirdly, the diversity and evolution of the endophytic bacteria in the tribe Vanguerieae was studied. Fourthly, the geographic distribution of the plant-bacteria association in Africa was investigated. Finally, a study on Burkholderia caledonica was carried out to test the genetic diversity within this species. Revision of Cuviera and Globulostylis (Vanguerieae)Generic circumscriptions within the tribe Vanguerieae (Rubiaceae) have been under discussion for a long time. Recent molecular studies, while providing new insights, have not yet solved all the problems. In this part the taxonomy and phylogeny of the Vanguerieae tribe are investigated, with a focus on the genus Cuviera s.l. A new and updated phylogenetic tree of the tribe is presented. On both molecular and morphological evidence, Cuviera is restricted to a group of ten West and Central African species. Globulostylis, previously included in Cuviera, is reinstated as a distinct genus, with eight species from Central Africa. Both genera are revised; the latter includes three new species (Globulostylis dewildeana, G. rammelooana, G. robbrechtiana) and two new combinations (G. leniochlamys and G. uncinula). The close relationship of both Cuviera s.s. and Globulostylis to Vangueriella is shown. Six aberrant species (most of them from EastAfrica) are excluded from Cuviera, but further work is needed before they can be confidently assigned to other genera. Endophytic bacteria in toxic South African plantsSouth African plant species of the genera Fadogia, Pavetta and Vangueria (all belonging to Rubiaceae) are known to cause gousiekte (literally ‘quick disease’), a fatal cardiotoxicosis of ruminants characterized by acute heart failure four to eight weeks after ingestion. Noteworthy is that all these species harbour endophytes in their leaves: nodulated bacteria in specializednodules in Pavetta and non-nodulated bacteria in the intercellular spaces between mesophyll cells in Fadogia and Vangueria. Isolation and analyses of these endophytes reveal the presence of Burkholderia bacteria in all plant species implicated in gousiekte. Although the nodulatedand non-nodulated bacteria belong to the same genus, they are phylogenetically not closely related and fall in different bacterial clades. P. harborii and P. schumanniana have their own specific endophyte – Candidatus B. harborii and Candidatus B. schumannianae – while the non-nodulatedbacteria found in the other gousiekte-inducing plants show high similarity to B. caledonica. In this group, the bacteria are host specific at population level. Investigation of gousiekte-inducing species from other African regions resulted in the discovery of the same endophytes. Several other plants of the genera Afrocanthium, Canthium, Keetia, Psydrax, Pygmaeothamnusand Pyrostria were studied and were found to lack bacterial endophytes. The discovery and identification of Burkholderia bacteria in gousiekte-inducing species open new perspectives and opportunities for research not only into the cause of this economically important disease, but also into the evolution and functional significance of bacterial endosymbiosis in Rubiaceae. The same bacteria are consistently found in gousiekte-inducing species from different regions indicating that these species will also be toxic to ruminants in other African countries, if the endophytes play a role in the disease.Endophytic Burkholderia in RubiaceaeSymbiotic ß-proteobacteria do not only occur in root nodules of legumes but are also found in leaves of certain Rubiaceae. The discovery of bacteria in plants formerly not implicated in endosymbiosis suggests a wider occurrence of plant-microbe interactions. Several ß-proteobacteria of the genus Burkholderia are detected in close association with tropical plants. This association is present in three separate phylogenetic clades, which suggests a recent and open plant-bacteria association. The presence or absence of Burkholderia endophytes is consistent at generic level and therefore implies a predictive value for the discovery of bacteria. Only a single Burkholderia species is found in association with a given plant species. However, the endophyte species are promiscuous and can be found in association with several plant species. Most of the endophytes are part of the plant-associated beneficial and environmental (PBE) group, but others are closely related to B. glathei. These soil bacteria, together with related nodulated and non-nodulated endophytes, are transferred to a newly defined and larger PBE group within the genus Burkholderia. Vanguerieae-Burkholderia association in Sub-Saharan AfricaIn Rubiaceae, certain species are known to be closely associated with endophytic leaf bacteria. These endophytes are either found in specialized leaf nodules or are freely distributed among the mesophyll cells. This second non-nodulated type of endosymbiosis was discovered in a few representatives of the Vanguerieae tribe of Rubiaceae and is especially known from South Africa. The identity of the endophytes was designated as Burkholderia, a genus known for its pathogens but also for its plant-associated representatives. For this part, our aim was to further document the Burkholderia diversity associated with Rubiaceae host plants and to establish whether the interaction is widespread in sub-Saharan Africa. Many representatives of the Vanguerieae tribe were investigated for the presence of endophytes. Special attention was paid to collect plants from different African regions in order to study the distribution range of the plant-bacteria association. The association is found in five different genera (Fadogia, Fadogiella, Globulostylis, Rytigynia, Vangueria) and is restricted to three clades. The endophytic bacteria belong to the genus Burkholderia and are part of the plant-associated beneficial and environmental (PBE) group. Some endophytes are very similar to B. caledonica, B. graminis, B. phenoliruptrix or B. phytofirmans, while others are classified in new OTUs that show no similarity with any previously named Burkholderia species. The association is not obligate for the bacterial partner and is considered a loose and recent interaction, which is demonstrated by the fact that the endophytescan be cultivated and that no coevolution occurs. The geographical distribution of the association is restricted by the distribution range of the host plants and comprises the whole of sub-Saharan Africa.Intraspecific variation in Burkholderia caledonicaThe best-known interaction between bacteria and plants is the legume-Rhizobium symbiosis, but other plant-bacteria interactions exist, such as between Rubiaceae and Burkholderia. It was demonstrated that a number of bacterial endophytes in Rubiaceae are closely related to the soil bacterium Burkholderia caledonica. This intriguing observation is here explored further by investigating B. caledonica isolates from different geographic regions and with different niches, namely free-living bacteria in soil and endophytic bacteria in host plants. By applying multilocus sequence analysis, we found that all these isolates belong to the species B. caledonica, but two genetically different groups are identified. Group A holds only European soil isolates and group B holds soil isolates from Africa, with the exception of one European soil isolate. This indicates a strong trend of biogeographic separation. Besides soil-dwelling bacteria, endophytic isolates of B.caledonica are also found in certain members of African Rubiaceae, but only in group B. These endophytes are closely related to the African soil isolates, which indicates a possible exchange of bacteria between soil and host plant.


Multi
Analysis of rice response and improvement of defence to the root-knot nematode Meloidogyne graminicola
Authors: ---
ISBN: 9789059896970 Year: 2014 Publisher: Gent Universiteit Gent. Faculteit Bio-Ingenieurswetenschappen

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