Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item INVESTIGATION INTO THE ROLE OF UVR8 IN BALANCING GROWTH AND ACCLIMATION TO UV-B RADIATION IN NATURAL AND TRANSGENIC POPULUS VARIANTS(2021) Wong, Tiffany Marie; Eisenstein, Edward; Sullivan, Joseph; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research on woody plants offers promise for the development of next-generation biofuel feedstocks with reduced lignin recalcitrance and enhanced saccharification for ethanol production. Natural variants of Populus trichocarpa with diverse lignin content and saccharification differences, and transgenic Populus deltoides constructed for reduced lignin levels for improved cellulose extraction, offer clues to enhance biofuel production but with a tradeoff to overall fitness and biomass. One concern of engineering lignin relates to the protection of plants against environmental stress such as UV-B radiation. Secondary metabolite biosynthesis initiated by UV-B, particularly phenylpropanoids (lignin precursors) and flavonoids, plays an important role in managing and protection of UV stress. Genetic modifications affecting the production of these compounds may have significant physiological consequences. Thus, the goal of this research was to develop a model for biosynthetic compensation of low-lignin Populus to UV-B stress. The effect of UV-B on Populus was evaluated by spectroscopic and metabolomic measurements on leaves. UV-B promoted shifts in physiological and metabolomic responses of natural and transgenic Populus with varying levels of lignin were complex, reflecting compensation from variety of biosynthetic alterations. Therefore, the impact of modulating the expression of the photoreceptor, UVR8, in regulating the response of Populus to UV-B was pursued. Modulation of UVR8 expression in Populus hybrid was achieved by constructing transgenic plants using CRISPR and RNAi, in wild-type, and an RNAi-constructed cinnamyl alcohol dehydrogenase knockdown line. UV-B response of UVR8 modulated Populus indicated that flavonoids were upregulated in UVR8 overexpression lines, and that in a CAD knockdown background, these effects were slightly enhanced. Salicylates were upregulated in UVR8 knockout poplars, suggesting metabolic flux in the pathway, but little difference was seen relative to wild-type plants in CAD lines, and UV-B treatment had little effect. An interesting and unexpected finding was that UVR8 modulated Populus exhibited more rapid growth than wild-type plants. The findings underscore the key role of UVR8 in synchronizing protective metabolic responses to UV-B and suggest an additional function of the photoreceptor in regulating growth and development of Populus through shifts in the chemical equilibria of UVR8 monomers and dimers and interactions with other regulatory factors.Item IDENTIFYING HIGHLY CONSERVED PATHOGENICITY GENES IN CHESTNUT BLIGHT AND POWDERY MILDEW FUNGI AS TARGETS FOR NOVEL FORMS OF HOST RESISTANCE(2019) Levine, Bruce Jonathan; Xiao, Shunyuan; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A bioinformatic search of the genomes of chestnut blight fungus, Cryphonectria parasitica (Cp), and the Arabidopsis powdery mildew fungus, Golovinomyces cichoracearum (Gc), yielded six suspected pathogenicity genes with homologues in both species. Deletion of these genes by homologous gene replacement was attempted in Cp, with one success, TG4. The TG4-knockout strain showed changes in phenotype and reduced fungal virulence against chestnut. TG4 appears to be a promising target for host-induced gene silencing (HIGS) in transgenic American chestnut. The use of homologues from genetically tractable species like Cp can help overcome the obstacles to performing reverse genetics on intractable, biotrophic fungi such as Gc. Experiments underway involving the silencing and ectopic overexpression of the Gc homologues of the target genes provide a rapid method to study Cp genes, including to screen additional candidate genes as future targets for HIGS.Item SYSTEMATICS OF THE GENUS COSMOSPORA (NECTRIACEAE, HYPOCREALES), AND COSPECIATION OF COSMOSPORA SPECIES WITH THEIR ASSOCIATED FUNGAL HOSTS.(2014) Herrera, Cesar Samuel; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cosmospora (in the broad sense; Nectriaceae, Hypocreales, Ascomycota) are fungi that parasitize other fungi, particularly fungi in the Xylariales (Ascomycota), or scale insects. Morphologically, these fungi are known for having one of the most simplest and smallest sexual fruiting bodies (<300 μm) among the Nectriaceae. The sexual spores are generally warted. The majority of Cosmospora species have acremonium-like or fusarium-like asexual states. The name Cosmospora is derived from the ornamentation in the sexual spores (Gr. cosmos = ornamented + Gr. spora = spore). The main goals of this dissertation were to revise Cosmospora sensu stricto, and to determine the evolutionary relationship between Cosmospora species and their associated fungal hosts. Additionally, Corallomycetella (Nectriaceae, Hypocreales, Ascomycota), a lineage basal to Cosmospora sensu lato, was revised as well. Molecular and classical taxonomic tools were used to revise the genera. A genus was recognized if the clade met the following criteria: 1) the clade was well supported, 2) the clade was associated with a unique asexual state, and 3) the clade was ecologically different. A species was recognized if the clade met the following criteria: 1) the clade was well supported in the majority of single gene trees, 2) the clade was morphologically different, and/or 3) the clade was ecologically different in regards to host. Cosmospora species were observed to be highly host specific. Thus, host was recognized as an important character to delineate species, and the host specificity led us to hypothesize that Cosmospora species and their associated hosts were cospeciation (i.e., their association was not random). Two new genera, nine new combinations, and eleven new species were described in the taxonomic work included in this dissertation. A significant global congruence was determined between the Cosmospora and host phylogenies. However, host-switch events seemed more abundant in the early lineages of the host, while cospeciation events seemed more common in more recent lineages of the host. This phylogenetic signature is consistent with pseudocospeciation, but it could not be confirmed given that divergence estimates could not be estimated.Item MOLECULAR PHYLOGENY AND TAXONOMIC REVISION OF FUNGI IN THE GENUS Thelonectria AND RELATED SPECIES WITH Cylindrocarpon-LIKE ANAMORPHS(2014) Salgado-Salazar, Catalina; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The genus Thelonectria and related species with Cylindrocarpon-like anamorphs are a group of perithecial ascomycetes in the family Nectriaceae that occur as saprobes and in few cases as pathogens of hardwood trees, shrubs or other plant substrates. Despite of being a key component of forest ecosystems around the world, species relationships and distribution are largely unknown. The objectives of this study were to: 1) infer species level phylogenetic relationships of the genus Thelonectria and related species with Cylindrocarpon-like anamorphs with uncertain classification, testing monophyly of each one of the groups studied; 2) delimit taxa, establishing taxon circumscriptions and providing brief descriptions; 3) resolve nomenclatural issues by identifying redundantly used names and synonyms; 4) provide identification tools, specifically, diagnostic keys and molecular data that can be used further as molecular barcodes; 4) provide distribution data and to take the first steps into the identification of speciation patterns observed in these fungi. To achieve these goals, herbarium materials, as well as freshly collected material obtained from the field or from fungal repositories were compared using phylogenetic analyses of multiple loci, morphology and geographic distribution. This research resulted in the narrower circumscription of the genus Thelonectria, not to contain one of the most common species in the group, T. jungneri. According to the results of the phylogenetic analyses it was found T. jungneri is a segregating clade that needs to be recognized as a different genus. For the genus Thelonectria, a total of 31 new species were described, and three new genera, closely related to Thelonectria were created to accommodate the diversity of other species with Cylindrocarpon-like anamorphs: Cinnamonectria gen nov. with C. cinnamomea as type taxon, Macronectria gen. nov. with M. jungneri as type taxon, and Tumenectria gen. nov. with T. laetidisca as type taxon. Species in this group of fungi present extensive morphological conservationism, representing a challenge for species identification without the use of molecular techniques, however offering a great opportunity to explore mechanisms of speciation and evolutionary diversification.Item NITROGEN REMOBILIZATION AND THE NUCLEOSIDE PHOSPHORYLASE-LIKE VEGETATIVE STORAGE PROTEIN FAMILY IN POPULUS: CHARACTERIZATION, REGULATION AND TRANSGENES(2012) Pettengill, Emily Ann; Coleman, Gary D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nutrient remobilization and storage allow plants to direct resources toward growth, maintenance and reproduction and redirect nutrients in response to environmental conditions or stresses. Particularly for perennial plants, these capabilities are critical to surviving periods of unfavorable growth such as winter and nutrient limited environments. In Populus, bark storage proteins (BSPs) have a dominant role in seasonal storage, and proteins related to BSPs, known as nucleoside phosphorylase-like (NP-like) proteins, can also participate in short-term storage. This research presents a comprehensive examination of the NP-like gene family by characterizing their expression, exploring evolutionary relationships within the plant kingdom and investigating metabolic regulation. I also developed and tested a set of qPCR reference genes to use for data normalization in two Populus species and four tissue-types. Lastly, transgenic trees were created to investigate the developmental or physiological functions of altered levels of BSP. Experiments characterizing the spatial and temporal expression of NP-like genes implicated a functional role for all members. Those results also support the phylogenetic analyses demonstrating the expansion of the gene family, which may have occurred through subfunctionalization. I also examined the regulation of carbon (C) and nitrogen (N) metabolites on the NP-like gene family expression and observed that amino acids, N compounds and gamma-aminobutyric acid (GABA) treatments modulate expression and likely have a role in regulatory pathways. By investigating transgenic trees with altered BSP levels, I present preliminary evidence that BSPs may have a role in nutrient signaling capable of modulating photosynthesis in young leaves. The results of this work deepen our understanding of nutrient remobilization and storage in Populus on regulatory, evolutionary and functional levels. Practically, the results can advance efforts to increase N use efficiency for sustainable biomass increases in Populus for use in agro-forestry, as biofuel feedstock, in phytoremediation and for carbon sequestration.