Global ETD Search

1	COEVOLUTION AND GENETIC DIVERSITY IN GRASS-ENDOPHYTE SYMBIOSES Craven, Kelly D. 01 January 2003 (has links) Symbioses between cool-season grasses (Subfamily Pooideae) and endophytic fungi in the genera Epichlo and Neotyphodium straddle a continuum of interactions from antagonistic to highly mutualistic. Although these two genera of endophytes are closely related, Neotyphodium endophytes are strictly seed-transmitted and provide many physiological and defensive benefits to their hosts, while Epichlo spp. have an obligately sexual contagious stage wherein host inflorescences are replaced by fungal sexual structures (stromata), effectively sterilizing the plant. Between these two extremes of interactions are Epichlo spp. with a mixed strategy, where some grass tillers are sterilized while others develop normally and yield healthy endophyte-infected seeds. These symbioses offer a unique opportunity to dissect evolutionary mechanisms that may drive movement along this continuum. The research presented characterizes distinct hybridization processes in endophytes and grasses that result in the generation of astounding genetic diversity for the symbiosis. Interspecific hybridization via hyphal anatomosis is a common feature of Neotyphodium endophytes, and may promote mutualism by combining suites of defensive alkaloid genes and ameliorating the adverse evolutionary effects of an asexual lifestyle. My results demonstrate that several genetically distinct hybrid endophytes infect grass species in tribe Poeae. Further, I show that a highly mutualistic asexual endophyte infecting tall fescue (=Festuca arundinaceum Schreb.), Neotyphodium coenophialum, also infects two closely related and interfertile relatives of this host. My findings suggest that this seed-borne endophyte may have been introgressed into these grasses through sexual grass hybridization events. These findings highlight interspecific hybridization as a means of generating tremendous genetic variability in both endophytes and their hosts, thus magnifying the adaptive evolutionary potential of these symbioses. Further, I establish a phylogenetic framework for grasses naturally harboring Epichlo and Neotyphodium endophytes. I show that patterns of genetic divergence among grass lineages are emulated by those of their fungal symbionts. These results suggest that endophytes have co-evolved with grasses in subfamily Pooideae, and may have played a critical role in the evolutionary success and radiation of this group of grasses.
2	Evolution of Vernalization and Photoperiod-Regulated Genetic Networks in the Grass Subfamily Pooideae McKeown, Meghan 01 January 2016 (has links) Flowering time is a carefully regulated trait that integrates cues from temperature and photoperiod to coordinate flowering at favorable times of the year. This dissertation aims to understand the evolution of genetic architecture that facilitated the transition of Pooideae, a subfamily of grass, from the tropics to the temperate northern hemisphere approximately 50 million years ago. Two traits hypothesized to have facilitated this evolutionary shift are the use of long-term low-temperature (vernalization) to ready plants for flowering, and long-day photoperiods to induce flowering. In chapter one I review literature on the regulation of grass flowering by vernalization and photoperiod, and in chapters two and three I determine the role of VERNALIZATION 1 (VRN1) and VRN2, known to confer vernalization responsiveness in core Pooideae crop species, in flowering time across Pooideae. In chapter four, I then test predictions of the hypothesis that the Brachypodium distachyon miR5200 ortholog in the ancestor of Pooideae was important for suppressing short day flowering through its negative regulation of flowering time integrator FLOWERING LOCUS T (FT)/VERNALIZATION3 (VRN3). In combination with other studies, my data demonstrate that VRN1-mediated vernalization responsiveness evolved early in the Pooideae, while VRN2-mediated vernalization responsiveness appears to have evolved much later in the diversification of Pooideae. Although miR5200 likely evolved early in the Pooideae, its transcriptional regulation by short day photoperiod appears derived within Brachypodium distachyon. This work answers important questions about the evolutionary origin of temperature- and photoperiod-mediated flowering in an economically important clade that contains crop species such as wheat (Triticum aestivum) and barley (Hordeum vulgare). Directions for future work on this topic are discussed in chapter 5. Development Evolution microRNA Pooideae Vernalization Evolution Plant Sciences
3	Phylogenetic Analysis of Subtribe Alopecurinae (Poaceae) Boudko, Ekaterina 12 March 2014 (has links) Subtribe Alopecurinae (Poeae, Poaceae) sensu lato‘s seven genera share interesting morphological similarities (dense spicate panicles and one-flowered spikelets) that were widely thought to have a common origin. However, recent molecular evidence for three of the genera has suggested that the subtribe may be polyphyletic. To test this, five DNA regions were sequenced and analyzed using phylogenetic methods. Results confirm that Alopecurinae s.l. as presently treated is polyphyletic and should be dissolved. Additionally, the genus Cornucopiae may be just another Alopecurus. Limnas and Pseudophleum are not closely allied to Alopecurus or each other, and are even further from Phleum. Phleum is a distinct lineage that is not closely allied to any other included Alopecurinae genus. Evidence for revising infrageneric classifications of Alopecurus and Phleum is presented, as is evidence for separating A. magellanicus into two or more subspecies. Poaceae Alopecurinae Poinae Poeae Phleinae Pooideae Phylogenetics Phylogeny Polyphyly Molecular Botany Taxonomy Systematics Alopecurus Phleum Beckmannia Limnas Cornucopiae Rhizocephalus Pseudophleum Plant Grass DNA sequencing trnT-trnL-trnF rpoB-trnC matK ITS ETS Convergent Evolution Hybridization Morphology Evolution Genetics Flora Subtribe
4	Phylogenetic Analysis of Subtribe Alopecurinae (Poaceae) Boudko, Ekaterina January 2014 (has links) Subtribe Alopecurinae (Poeae, Poaceae) sensu lato‘s seven genera share interesting morphological similarities (dense spicate panicles and one-flowered spikelets) that were widely thought to have a common origin. However, recent molecular evidence for three of the genera has suggested that the subtribe may be polyphyletic. To test this, five DNA regions were sequenced and analyzed using phylogenetic methods. Results confirm that Alopecurinae s.l. as presently treated is polyphyletic and should be dissolved. Additionally, the genus Cornucopiae may be just another Alopecurus. Limnas and Pseudophleum are not closely allied to Alopecurus or each other, and are even further from Phleum. Phleum is a distinct lineage that is not closely allied to any other included Alopecurinae genus. Evidence for revising infrageneric classifications of Alopecurus and Phleum is presented, as is evidence for separating A. magellanicus into two or more subspecies. Poaceae Alopecurinae Poinae Poeae Phleinae Pooideae Phylogenetics Phylogeny Polyphyly Molecular Botany Taxonomy Systematics Alopecurus Phleum Beckmannia Limnas Cornucopiae Rhizocephalus Pseudophleum Plant Grass DNA sequencing trnT-trnL-trnF rpoB-trnC matK ITS ETS Convergent Evolution Hybridization Morphology Evolution Genetics Flora Subtribe

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