Verticillium longisporum ist ein bodenbürtiges vaskuläres Pflanzenpathogen, das im europäischen Raum eine ernsthafte Bedrohung des agronomisch wichtigen Raps, einer Quelle für Biokraftstoff und Speiseöl, darstellt. Infektionsanalysen mit V. longisporum zeigten in der Modellpflanze Arabidopsis thaliana eine neue Funktion des Jasmonoyl-Isoleucin- (JA-Ile) Rezeptors COI1, die unabhängig von JA-Ile oder pilzlichen Analoga dieses Pflanzenhormons Suszeptibilität gegenüber dem Pathogen vermittelt. Pfropfungsexperimente führten zu der Erkenntniss, das COI1 in Wurzeln für die Ausprägung von Krankheitssymptomen im Spross benötigt wird (Ralhan et al., 2012). Im Rahmen dieser Arbeit wurde der Frage nachgegangen, welche Gene unter der Kontrolle der JA-Ile-unabhängigen COI1-Funktion stehen und inwieweit sich die Signaltransduktionskette von der bekannten, durch COI1 aktivierten, Signaltransduktion unterscheidet. RNA-Sequenz-Analysen von infizierten und nicht-infizierten Wurzeln des Wildtyps, der coi1-Mutante und der JA-Biosynthesemutante aos ergaben zunächst, dass unter den gewählten Infektionsbedingungen nur wenige Gene durch den Pilz beeinflusst werden. Beim Vergleich der Transkriptomdaten von coi1- und aos-Wurzeln fiel jedoch auf, dass eine Gruppe von 113 Genen in der coi1-Mutante konstitutiv stärker exprimiert wurde als in der JA-Biosynthesemutante. Im Gegensatz dazu gab es nur wenige Gene, die in der coi1-Mutante geringer exprimiert waren als in aos und deren Expressionsmuster sich in unabhängigen Proben als nicht reproduzierbar erwies. Als Markergene für die Gruppe von Genen, bei der COI1 unabhängig von JA-Ile, d.h. auch in der aos-Mutante, als negativer Regulator der Genexpression wirkt, wurden aufgrund robuster Effekte der hochregulierten Transkriptmenge in der coi1-Mutante die Gene Phosphoglyceratmutase, Germin 2 und Cysteine-rich Receptor-like Kinase 15 (CRK15) gewählt. Durch Mutationen der Ligandenbindestelle von COI1 für JA-Ile wurde gezeigt, dass ein mutiertes COI1-Protein, das in der Pflanze JA-Ile-abhängige Funktionen wie Fertilität, JA-sensitives Wurzelwachstum und JA-induzierbare JAZ10-Expression nicht mehr ausführen konnte, ähnlich wie das WT-COI1 die Expression der Markergene weiterhin reprimieren konnte. Die Suszeptibilität-vermittelnde JA-Ile-unabhängige Funktion von COI1 gegenüber V. longisporum konnte mit diesen Konstrukten jedoch nicht eindeutig gezeigt werden, da die entsprechenden Leervektorkontrollen unerwarteterweise stark ausgeprägte Krankheitssymptome nach Infektion mit V. longisporum aufwiesen. Weitere bekannte Signalkomponenten der JA-Signaltransduktion wurden bezüglich ihrer Rolle in der JA-Ile-unabhängigen Funktion des COI1-Proteins analysiert. Dabei konnte über die Beteiligung der JAZ-Proteine keine Aussage getroffen werden, da eine beschriebene dominant-negative Wirkung des JAZ1∆3-Proteins in dieser Arbeit nicht bestätigt werden konnte. Da-hingegen konnte gezeigt werden, dass Komponenten wie NINJA und MYC2,3,4 keinen Einfluss auf die reprimierende Funktion von COI1 bezüglich der Phosphoglyceratmutase haben. Demnach konnte in dieser Arbeit durch Expressionsanalysen der Phosphoglyceratmutase, einem Schlüsselenzym der Glykolyse, demonstriert werden, dass sich die neue Funktion von COI1 stark von der klassischen und bekannten Funktion als JA-Ile-Rezeptor und Aktivator downstream agierender Prozesse der JA-Signaltransduktion unterscheidet. Es wird postuliert, dass es sich dabei um eine anzestrale Funktion des Proteins handelt, die mit der Entwicklung der JA-Synthese in Pflanzen aufgrund hoher Affinität des Rezeptors zu seinem Liganden in den Hintergrund gestellt wurde.

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Not available / text

published_or_final_version / abstract / Botany / Master / Master of Philosophy

The cyclic nucleotide monophosphates (CNs), cAMP and cGMP, are second messengers that participate in the regulation of development, metabolism and adaptive responses. In plants, CNs are associated with the control of pathogen responses, pollen tube orientation, abiotic stress response, membrane transport regulation, stomatal movement and light perception. In this study, we hypothesize that cAMP and cGMP promote changes in the transcription level of genes related to photosynthesis, high light and membrane transport in Arabidopsis thaliana leaves and, that these changes at the molecular level can have functional biological consequences. For this reason we tested if CNs modulate the photosynthetic rate, responses to high light and root ion transport. Real time quantitative PCR was used to assess transcription levels of selected genes and infrared gas analyzers coupled to fluorescence sensors were used to measure the photosynthetic parameters. We present evidence that both cAMP and cGMP modulate foliar mRNA levels early after stimulation. The two CNs trigger different responses indicating that the signals have specificity. A comparison of proteomic and transcriptional changes suggest that both transcriptional and post-transcriptional mechanisms are modulated by CNs. cGMP up-regulates the mRNA levels of components of the photosynthesis and carbon metabolism. However, neither cAMP nor cGMP trigger differences in the rate of carbon assimilation, maximum efficiency of the photosystem II (PSII), or PSII operating efficiency. It was also demonstrated that CN regulate the expression of its own targets, the cyclic nucleotide gated channels - CNGC. Further studies are needed to identify the components of the signaling transduction pathway that mediate cellular changes and their respective regulatory and/or signaling roles.

No description available.

No description available.

Transposons are a diverse collection of mobile genetic elements and are important components of nearly every genome. Because of their mobile and repetitive nature, transposons can have considerable effects on host gene expression, genome organization and evolution. The recent availability of genomic sequence information has expedited the discovery and study of transposons, as exemplified in this thesis by the complete genome analysis of the model plant system Arabidopsis thaliana. Data mining in Arabidopsis has revealed a rich diversity of transposons, of which Basho and Terminal-repeat Retrotransposons In Miniature (TRIM) elements were previously unknown types. The identification of Related to Empty Sites (RESites) provide evidence for past transposition events. Examples of elements contributing to coding regions, acquiring cellular sequences, along with in-depth analysis of the insertions, their target sites and their distribution illustrate the impact of transposons on gene and genome structures. Computer-based searches of genomic sequences has also improved our understanding of previously identified transposon families, such as the origin, classification and mobilization of Tourist elements. In addition, information on transposons gathered from in silico analysis of genomic sequences has served to design in vivo experiments. In a whole genome strategy, Transposon Display was used to investigate transposition and regulation of mobility of Tourist-like elements in A. thaliana and in the nematode Caenorhabditis elegans.

Abscisic acid (ABA) is a key plant hormone regulating agronomically important processes including seed maturation and dormancy, stomatal opening and closure, along with the transcriptional and physiological response of plants to abiotic and biotic stresses. The current study sought to functionally characterize members of an ABA-responsive gene family encoding GRAM (Glucosyltransferases, Rab-like GTPase activators and Myotubularins) domain proteins in Arabidopsis thaliana. Utilizing reverse genetics loss- and gain-of-function lines associated with GEM-RELATED 5 (GER5) were obtained, which displayed several defects in reproductive development. Gene expression profiling, RNA in situ hybridization and immunohistochemical techniques were utilized to evaluate GER5 and two closely related GRAM genes, GEM-RELATED 1 (GER1) and GLABRA2 EXPRESSION MODULATOR (GEM) in reproductive structures. Microarray profiling of seeds from ger5-2 mutants and wild-type plants revealed transcriptional changes in carbohydrate metabolism, hormone signaling and catabolic processes accompanied seed development defects of ger5-2 mutants. Seed germination assays further revealed ger5-2 mutants exhibited reduced sensitivity to ABA. In assessing GER5, GER1 and GEM as putative ABA-response genes, a second study evaluated the expression of GRAM, AuTophaGy-related (ATG), and ABA-response genes in source and sink organs exposed to abiotic stress or within mutant backgrounds deficient in sugar signaling. Monodansylcadaverine (MDC) staining was also utilized to localize autophagosomes or autophagic bodies within vegetative or reproductive organs during plant development, or in response to carbon starvation or abiotic stress. In a third study transcriptional differences in ABA metabolism, transport and homeostasis were examined within reproductive organs (cauline leaves, inflorescence meristem, developing siliques) exposed to cold and heat stress. This study revealed reproductive organs are characterized by unique patterns of ABA metabolism which differ from tissues typically associated with classical ABA responses. Together, these studies indicate GER5, an uncharacterized ABA-responsive GRAM domain gene, plays a novel role in the reproductive development of plants and that ABA metabolism and signaling are uniquely regulated in reproductive organs.

An alkaline extract of the brown seaweed, Ascophyllum nodosum (ANE) increases plant growth and imparts resistance against biotic stresses. However, little is known of the effects of ANE on insects. Myzus persicae, green peach aphid (GPA), and Arabidopsis model were used to determine whether application of ANE confers protection from GPA infestation. GPA colonization increased in ANE treated plants, associated with improved biomass. However, ANE treated plants exhibited less cell death and also showed a greater ability to recover from GPA injury. Lower expression of SAG13, SAG21 and CHL1 and a higher expression of ARR5 was observed in ANE treated plants. Taken together, gene expression along with lower cell death suggests ANE may delay senescence in Arabidopsis. Delayed senescence in Arabidopsis following ANE treatment may be a result of increased cytokinin activity. Increased GPA numbers could be, at least in part, due to delayed senescence in Arabidopsis following ANE treatment.