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Chaetanthera Ruiz & Pav. (30 species, 1 variety, 2 hybrid forms) and Oriastrum Poepp. & Endl. (18 species, 1 variety) are among the most species-rich Astereaceae genera of the Chilean Flora. Formerly combined under one name, the two genera have been extensively revised. Chaetanthera is found mainly in Chile, with one Peruvian species and several scattered populations of other species in Andean Argentina. Oriastrum inhabits the higher elevations of the Andes, spread over Chile, Argentina, Bolivia and Peru. Systematic studies focussing on morphological and anatomical variation of characters taken from habit, involucral bracts, and achenes, combined with palynological and genetic (nr DNA) information are used to circumscribe Chaetanthera with two subgenera – Chaetanthera subgenus Chaetanthera and Chaetanthera subgenus Tylloma (D.Don) Less., and reinstate Oriastrum with two subgenera – Oriastrum subgenus Oriastrum and Oriastrum subgenus Egania (J.Rémy) A.M.R. Davies.
Character variation is discussed in the context of form, function and habitat, with emphasis on the evolutionary adaptiveness of character traits seen in the two allied genera. Chaetanthera appears to show primary adaptation to cold and several secondary adaptations to arid conditions, typical of modern Chilean landscapes. Oriastrum taxa appear well-adapted to the cold, high elevations of the Andes, and show secondary developments trending towards an insular syndrome.
The collated bio-geographical information of the taxa is considered in terms of endemism, hotspots and species radiations. Chaetanthera taxa have 2 loci of diversity hotspots in Chile – in Coquimbo and in Santiago. Trichome diversity and capitula morphology trends are used as evidence of species radiations in Chaetanthera. Oriastrum taxa are notable for parallel radiations of morphologically similar species within particular Andean zones: i.e., Altoandino or Altiplano.
Case studies concerning three groups of Chaetanthera taxa are presented. The first case highlights the effect of the El Niño on the polymorphic C. glabrata along the Chilean Pacific coast. The second case deals with current active hybridisation between C. linearis and C. albiflora in the semi-arid Andean foothills. In the last example, incipient speciation and polymorphism between C. chilensis and C. elegans in southern Central Chile is discussed. Various statistical techniques for the analysis of hybridisation events are applied.
All taxa are keyed out and described. Novel taxa are described and imaged or illustrated. Nomenclatural issues and lectotypification of 15 Chaetanthera names and 6 Oriastrum names are effected. Chaetanthera is described here with one novel species (C. pubescens A.M.R. Davies), one novel variety (C. glandulosa var. microphylla A.M.R. Davies), a new name (C. frayjorgensis A.M.R. Davies), and three new combinations: C. albiflora (Phil.) A.M.R. Davies, C. depauperata (Hook. & Arn.) A.M.R. Davies, C. taltalensis (Cabrera) A.M.R. Davies. Oriastrum is described here with four new species and one new variety: O. werdermannii A.M.R. Davies, O. famatinae A.M.R. Davies, O. tarapacensis A.M.R. Davies, O. tontalensis A.M.R. Davies and O. stuebelii var. cryptum A.M.R. Davies respectively. Five novel combinations are presented: O. abbreviatum (Cabrera) A.M.R. Davies, O. achenohirsutum (Tombesi) A.M.R. Davies, O. apiculatum (J.Rémy) A.M.R. Davies, O. revolutum (Phil.) A.M.R. Davies and O. stuebelii (Hieron.) A.M.R. Davies var. stuebelii. -
Plant beneficial microorganisms, such as arbuscular mycorrhiza fungi (AMF), increasingly attract
scientific and agronomic attention due to their capacity to increase nutrient accessibility for plants
and to reduce inorganic fertilizer requirements. AMF are thought to form symbioses with most land
plants, obtaining carbon from the autotrophic host whilst enhancing uptake of poorly available
nutrients.
The species of AMF are mainly identified by spore morphology, which is time consuming, requires
expertise and is rarely applicable to AMF identification in roots. Molecular tools such as analysis of
standardized DNA fragment sequences may allow the recognition of species through a ‘DNA
barcode’, which may partly overcome this problem. The focus of this study was to evaluate
different regions of widely used rDNA repeats for their use as DNA barcodes for AMF including the
small subunit rRNA gene (SSU), the internal transcribed spacer (ITS) and the large subunit rRNA
gene (LSU). Closely related species in the genus Ambispora, members of which have dimorphic
spores, could not be separated by analysis of the SSU region, but of the ITS region. Consequently,
the SSU was not used for subsequent analysis, but a DNA fragment covering a small part of the
SSU, the entire ITS region and about 800 bp of the LSU (SSUmCf-LSUmBr fragment) was
analysed, providing phylogenetic resolution to species. New AMF specific primers for these
potential barcoding regions were developed and can be applied, without amplification of non-target
organisms, for AMF species determination, including identification from field and root samples.
Analyses based on the application of the SSUmCf-LSUmBr fragment showed that the widely used
AMF model organism Glomus sp. DAOM197198 (formerly called Glomus intraradices) is not
conspecific with Gl. intraradices. The SSUmCf-LSUmBr fragment clearly provides a much higher
species resolution capacity when compared with the formerly preferred ITS and LSU regions.
Further study of several groups of AMF species using different regions of the SSUmCf-LSUmBr
fragment revealed that only the complete SSUmCf-LSUmBr fragment allowed separation of all
analysed species. Based on these results, an extended DNA barcode covering the ITS region and
parts of the LSU region is suggested as a DNA barcode for AMF. The complete SSUmCf-LSUmBr
fragment sequences can serve as a database backbone for also using smaller rDNA fragments as
barcodes. Although the smallest fragment (approximately 400 bp) analysed in this study was not
able to discriminate among AMF species completely, such short regions covering the ITS2 or LSU
D2 regions, respectively, would most likely be suitable for community analyses with 454 GS-FLX
Titanium sequencing, providing that the analyses is based on the longer DNA sequences. -
Diese Arbeit behandelt die Entwicklung und Evaluation eines computergestützten Informationssystems zum Thema Biodiversität sowie dessen Einsatz mit Schulklassen in einem Naturkundemuseum. Die Erhaltung der biologischen Vielfalt wird als eine der größten Aufgaben für die Menschheit erachtet. Bereits Kinder und Jugendliche sollten an das Thema herangeführt werden, um sie auf umweltgerechtes Entscheiden und Handeln vorzubereiten. Das Thema Biodiversität mit seinen Aspekten Vielfalt der Erbinformationen, Arten und Ökosysteme ist Schülerinnen und Schülern jedoch kaum bekannt. Ziel war es daher, vor allem jungen Menschen mithilfe des computergestützten Informationssystems einen interessanten und informativen Zugang zum Thema Biodiversität bereitzustellen. Der Einsatz von Computern im außerschulischen Unterricht, z.B. in Naturkundemuseen, ist bislang wenig empirisch erforscht. Forschungsbedarf besteht auch in der fachdidaktischen Umsetzung des Themas Biodiversität. Die durchgeführten Untersuchungen werden durch ein Rahmenmodell für das Lernen an außerschulischen Bildungseinrichtungen, das „Contextual Model of Learning“ von Falk und Dierking, theoretisch eingefasst. In der ersten Projektphase wurde das Informationssystem entwickelt und unter Einbindung von über tausend Schülerinnen und Schülern im Alter von zehn bis achtzehn Jahren in Hinblick auf kognitive und motivationale Wirkungen sowie Nutzerfreundlichkeit untersucht. Die Ergebnisse zeigen einen signifikanten Lernzuwachs von Prä- zu Posttest sowie eine gute Akzeptanz und Nutzerfreundlichkeit. Durch Log-Files aufgezeichnete Navigationspfade verweisen auf den Zusammenhang zwischen vorab bekundetem Interesse an Tieren und Pflanzen und tatsächlichem Nutzerverhalten. In der zweiten Projektphase wurden Wissenserwerb und Motivation bei der Nutzung des computergestützten Informationssystems in Verbindung mit den Ausstellungsobjekten des Naturkundemuseums als Feldstudie erforscht. Knapp 150 Schülerinnen und Schüler im Alter von elf bis fünfzehn Jahren nahmen an der Prä-Posttest-Fragebogenstudie teil. Von Arbeitsblättern geleitet, erkundeten die Testpersonen selbstständig das Museum, wobei sie bei bestimmten Aufgabenstellungen freie Wahl hatten zwischen den Medientypen Computer und Ausstellungsobjekt. Durch den gezielten Medieneinsatz wurde den Schülern Basiswissen über das Thema Biodiversität vermittelt; die Arbeitsblätter unterstützten den Lernprozess. Der Computer wurde häufig für Recherchezwecke ausgewählt. Das Informationssystem wurde als lehrreiche und motivierende Ergänzung der Ausstellungsobjekte gewertet.
Auf Basis der Forschungsergebnisse bietet diese Arbeit abschließend Hinweise zur Einbindung des Themas Biodiversität in den Unterricht; sie greift noch zu verwirklichende Forschungsaspekte im Bereich Museumslernen auf und diskutiert die Rolle des „Contextual Model of Learning“ für künftige Studien in außerschulischen Bildungseinrichtungen. -
Monomeric actin controls the activity of the transcription factor Serum Response Factor (SRF) via its coactivator MAL/MRTF-A. Upon signal induction, MAL is released from actin, binds SRF and activates target gene expression. In order to characterise the physiological role of this signalling pathway, I screened on a genome wide basis for target genes by transcriptome analysis.
A combination of actin binding drugs (Cytochalasin D and Latrunculin B), targeting monomeric actin, was used to specifically and differentially interfere with the complex between MAL and actin. 210 genes primarily controlled by monomeric actin were identified in mouse fibroblasts. Among them more than 30% have been already found in screens for SRF target genes, supporting the validity of the screening approach. As expected, a lot of genes were involved in cytoskeleton organization. However, genes having anti-proliferative or pro-apoptotic features were identified surprisingly to the same extent. Consistently, I could demonstrate an antiproliferative function of MAL. More specifically, several genes interfering with the MAPK pathway were identified.
One of them was Mig6/Errfi1, a negative regulator of EGF receptors. Mig6 induction by LPA or FCS revealed to be dependent on MAL, monomeric actin and the small GTPases Rho. Activated forms of MAL or SRF were sufficient to induce Mig6 expression. Subsequently, a Mig6 promoter element was found to be necessary to mediate MAL/SRF induction. Moreover, induction of Mig6 through the Actin-MAL pathway led to the downregulation of the mitogenic EGFR-MAP kinase cascade. For the first time a transcriptional link between G-actin levels sensed by MAL and the regulation of EGFR signalling was established.
Furthermore, after having demonstrated that MAL induces apoptosis, I focused on the characterisation of two proapototic targets identified in the screen: Bok and Noxa. Bok and Noxa were induced by activators of the Rho-Actin-Mal-Srf pathway on a MAL dependent manner. The study of the Bok promoter revealed the existence of a response element that was necessary for the induction by MAL-SRF. Interestingly, apoptotic inducers like staurosporine, TNFα, or the DNA damaging agent Doxorubicin triggered MAL-SRF mediated transcription. As SRF controls the expression of the anti-apoptotic genes Bcl2 and Mcl1, the results from this work places thus SRF as a key transcription factor controlling the balance between pro and anti apoptotic genes in response to external cues. -
Pathological changes in the dopaminergic system account for a number of devastating illnesses including schizophrenia, psychosis, depression, addiction, obsessive compulsive disorder or the most well known Parkinson’s disease (PD). The nigrostriatal pathway is an important component of the dopaminergic (DA) system mediating voluntary movement and originates in the ventral midbrain from where substantia nigra pars compacta (SN) neurons send their axons to the dorsal striatum. Massive loss of SN neurons as seen in PD leads to postural imbalance, rigidity, tremor and bradykinesia, however, the precise mechanisms involved in the maintenance and the demise of SN neurons are poorly understood.
Endogenous neurotrophic factors such as the Glial cell line-derived neurotrophic factor (GDNF; signaling via the Ret receptor tyrosine kinase) and Brain-derived neurotrophic factor (BDNF; signaling via the TrkB receptor tyrosine kinase) were reported to have protective and rescuing properties on DA neurons; however, their physiological roles in SN neurons remained unknown. Inactivation of the oxidative stress suppressor DJ-1 causes PD; remarkably, mice lacking DJ-1 function do not display overt SN degeneration, suggesting that additional DJ-1 interactors compensate for loss of DJ-1 function. To begin characterizing the cellular and molecular networks mediating SN neuron survival, I used mouse genetics to investigate the roles and the interaction between GDNF/BDNF-mediated trophic signaling and the DJ-1-mediated stress response in SN neurons.
While mice lacking TrkB function specifically in SN neurons display a normal complement of SN neurons up to 24-months, loss of Ret function in DA neurons causes adult-onset and progressive SN degeneration, suggesting that GDNF/Ret signaling is required for long-term maintenance of SN neurons. I then generated and aged mice lacking Ret and DJ-1 and found remarkably that they display an enhanced SN degeneration relative to mice lacking Ret. Thus, DJ-1 promotes survival of Ret-deprived SN neurons. Interestingly, the survival requirement for Ret and DJ-1 is restricted to those SN neurons which express the ion channel GIRK2, project exclusively to the striatum and specifically degenerate in PD. This is the first in vivo evidence for a pro-survival role of DJ-1.
To understand how DJ-1 interacts molecularly with Ret signaling, I performed epistasis analysis in Drosophila melanogaster. Although DJ-1 orthologs DJ-1A and DJ-1B are dispensable for fly development, the developmental defects induced by targeting constitutively active Ret to the retina were suppressed in a background of reduced DJ-1A/B function. Moreover, DJ-1A/B interacted genetically with Ras/ERK, but not PI3K/Akt signaling to regulate photoreceptor neuron development. Flies with reduced ERK activity and lacking DJ-1B function had more severe defects in photoreceptor neuron and wing development than flies with reduced ERK function. These observations establish, for the first time, a physiological role for DJ-1B in the intact Drosophila.
Our findings suggest that the triple interaction between aging, trophic insufficiency and cellular stress may cause Parkinsonism. Because Ret and DJ-1 show convergence of their pro-survival activities, we predict that striatal delivery of GDNF might be most effective in PD patients carrying DJ-1 mutations. A better understanding of the molecular connections between trophic signaling, cellular stress and aging will accelerate the process of drug development in PD. - Mostrar más
