<p> Most plants harbor microbial symbionts, which often affect host performance and fitness. Endophytic <i>Epichlo&euml;</i> species are systemic fungal microbial symbionts of many cool-season pooid grasses. Benefits to the host from <i>Epichlo&euml;</i> infection include increased resistance to stressful environmental factors, such as drought and limited soil nutrients, due to morphological and physiological changes. The major benefit of <i> Epichloe</i> infection is enhanced protection against herbivory due to production of fungal alkaloids. The fungal alkaloids have varying activity against invertebrate or mammalian grazers. Although <i>Epichlo&euml; </i> endophytes are well-studied in agronomic grasses such as tall fescue and perennial ryegrass, little is known about the how the presence of different endophyte species and their frequencies and distribution are related to environmental factors in native grasses. Using two native grasses to eastern [<i>Poa alsodes</i> (Grove Bluegrass)] and western [<i>Achnatherum robustum </i> (Sleepygrass)] North America, I addressed the following questions: 1) how are endophyte species distributed among populations along a latitudinal gradient, 2) what fungal alkaloids are produced by different endophyte species, 3) how do fungal alkaloids affect insect herbivores, and 4) what are the effects of different endophytes on host plant growth? (Abstract shortened by ProQuest.) </p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4231. Adviser: James W. Dalling. Includes bibliographical references (leaves 103-116) Available on microfilm from Pro Quest Information and Learning.

<p> Coral reef ecosystems worldwide are facing increasing degradation due to disease, anthropogenic damage, and climate change, particularly in the Tropical Western Atlantic. Mesophotic coral ecosystems (MCEs) have been recently gaining attention through increased characterization as continuations of shallow reefs below traditional SCUBA depths (>30 m). As MCEs appear to be sheltered from many stressors affecting shallow reefs, MCEs may act as a coral refuge and provide larvae to nearby shallow reefs. The Deep Reef Refugia Hypothesis (DRRH) posits that shallow and mesophotic reefs may be genetically connected and that some coral species are equally compatible in both habitats. The research presented here addresses key questions that underlie this theory and advances our knowledge of coral connectivity and MCE ecology using the depth-generalist coral <i>Montastraea cavernosa</i>. Chapter 1 presents an overview of the DRRH, a description of MCEs in the Gulf of Mexico (GOM), and the framework of research questions within existing reef management infrastructure in the GOM. Through microsatellite genotyping, Chapter 2 identifies high connectivity among shallow and mesophotic reefs in the northwest GOM and evidence for relative isolation between depth zones in Belize and the southeast GOM. Historical migration and vertical connectivity models estimate Gulf-wide population panmixia. Chapter 3 focuses on population structure within the northwest GOM, identifying a lack of significant population structure. Dominant migration patterns estimate population panmixia, suggesting mesophotic populations currently considered for National Marine Sanctuary protection benefit the Flower Garden Banks. Chapter 4 quantifies the level of morphological variation between shallow and mesophotic <i>M. cavernosa</i>, revealing two distinct morphotypes possibly representing adaptive tradeoffs. Chapter 5 examines the transcriptomic mechanisms behind coral plasticity between depth zones, discovering a consistent response to mesophotic conditions across regions. Additionally, variable plasticity of mesophotic corals resulting from transplantation to shallow depths and potential differences in bleaching resilience between shallow and mesophotic corals are identified. The dissertation concludes with a synthesis of the results as they pertain to connectivity of shallow and mesophotic corals in the Gulf of Mexico and suggests future research that will aid in further understanding of MCE ecology and connectivity.</p><p>

<p> <i>Sinorhizobium meliloti</i> is a Gram-negative alphaproteobacterium and nitrogen-fixing symbiont, which undergoes a novel cell cycle modification during its' host-microbe interaction. I intend to monitor the transcriptional regulation of cell cycle-related genes during free-loving growth, in addition to monitoring their expression during symbiosis. Using genes known to be regulated by CtrA in <i>C. crescentus</i> or predicted to be regulated by CtrA in <i>S. meliloti,</i> I aim to show how certain cell cycle genes are regulated in <i>S. meliloti.</i> In <i>C. crescentus, </i> CtrA acts as a transcription factor that is active when phosphorylated and inactive when not phosphorylated. In <i>S. meliloti,</i> CbrA is a histidine kinase that ultimately inhibits CtrA phosphorylation. Using a &Delta;<i>cbrA</i> null mutant, which leads to increased levels of CtrA in <i>S. meliloti,</i> and the &beta;-glucuronidase (GUS) reporter gene, I can monitor the expression levels of target genes that are potentially regulated by CbrA and CtrA. Promoter regions, transcription start sites, and translation start sites of target genes have been cloned into the plasmid pVO155 upstream of the GUS gene. I measured the GUS enzymatic activity using the 4-methylumelliferyl-beta-D-glucuronide (MUG) substrate. Additionally, after infecting <i>Medicago sativa</i> seedlings with these fusions strains, I used a different GUS substrate to test for the presence of target gene expression in root nodules. Results thus far have shown some target genes with large differences in expression coinciding with the absence of <i> cbrA</i> and increased CtrA levels while some target genes show only slight differences, if any at all. Tracking the expression location and patterns of target genes in root nodules has shown that some genes are expressed ubiquitously throughout the nodule while other genes are expressed in specific locations. These results are significant because no one has looked at genes regulated by CbrA or CtrA in <i>S. meliloti,</i> which is more applicable to host-microbe interactions than <i>C. crescentus,</i> especially since <i>Agrobacterium tumefaciens</i> and <i>Brucella abortus </i> both have a CbrA homologue. Additionally, I will provide critical insight into the molecular biology of the <i>S. meliloti</i> host-microbe interaction.</p>

Thesis (Ph.D.)--University of California, Berkeley, 2006. / (UMI)AAI3254111. Source: Dissertation Abstracts International, Volume: 68-02, Section: B, page: 0763. Adviser: Jillian F. Banfield.