Evolution and Expression of polyketide synthase gene in the lichen-forming fungal families Cladoniaceae and Ramalinaceae

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dc.contributor.supervisor Piercey-Normore, Michele (Biological Sciences) en_US
dc.contributor.author Timsina, Brinda Adhikari
dc.date.accessioned 2014-01-17T18:41:43Z
dc.date.available 2014-01-17T18:41:43Z
dc.date.issued 2012-12 en_US
dc.date.issued 2012 en_US
dc.identifier.citation Timsina, Brinda A., Stocker-Wörgötter, E., and Piercey-Normore, Michele D. (2012). Monophyly of some North American species of Ramalina and inferred polyketide synthase gene function. Botany, 90(12): 1295-1307 en_US
dc.identifier.citation Deduke C., Timsina B. A, and Piercey-Normore M. D. 2012. Effect of Environmental Change on Secondary Metabolite Production in Lichen-Forming Fungi. pp. 197-230 In: Young, SS. and Silvern, SE. (Eds.), International Perspectives on Global Environmental Change. InTech. ISBN: 978-953-307-815-1. en_US
dc.identifier.uri http://hdl.handle.net/1993/23271
dc.description.abstract Fungal polyketides are synthesized by polyketide synthases (PKS) encoded by PKS genes. The function of many PKS genes is unknown and the number of PKS genes exceeds the number of polyketides in many genomes. The lichen-forming fungi, Cladonia and Ramalina have chemical variants separated by habitat suggesting that environmental conditions may influence polyketide production. The goal of this thesis was to examine evolutionary relationships as a framework to investigate PKS gene function in the lichen-forming fungal families Cladoniaceae and Ramalinaceae. A phylogenetic analysis of the genus Ramalina (Chapter 2) using nuclear and mitochondrial ribosomal DNA sequences showed monophyly for seven species and included three species, which were not examined in phylogenies prior to this study. One monophyletic species, R. dilacerata was chosen for further tests of the effect of growing conditions on PKS gene expression (Chapter 3). Growth media containing yeast extracts produced the largest colony diameters and the fewest number of polyketides. A significant negative relationship occurred between colony diameter and number of secondary metabolites. Expression of two types of PKS genes was correlated with pH-level and media conditions that produced larger numbers of secondary products in R. dilacerata. A PKS gene phylogeny was constructed for 12 paralogs detected in members of the C. chlorophaea complex (Chapter 4) and gene selection was inferred using dN/dS estimations. The gene phylogeny provided evidence for independent origins and purifying and positive selection of PKS paralogs. This research provided insight into the evolution of PKS genes in the C. chlorophaea complex and identified potential genes that produce non-reduced polyketides present in C. chlorophaea. This thesis provided evidence for diversification of both morphological and chemical species and monophyly of previously unstudied Ramalina species. This research also supported theories of secondary metabolite synthesis based on growing conditions of R. dilacerata, and it revealed that PKS genes under selection in the Cladonia chlorophaea group provide the lichen with the adaptive capacity to survive under variable conditions. Knowledge of the ecological function of fungal polyketides can be valuable for conservation management and policy makers; and for understanding the potential pharmaceutical roles of these natural products. en_US
dc.publisher NRC Research Press en_US
dc.publisher InTech open access publisher en_US
dc.subject Evolution en_US
dc.subject Gene expression en_US
dc.subject Polyketide synthase en_US
dc.subject paralogs en_US
dc.subject Lichen-fungi en_US
dc.subject Culture en_US
dc.subject mycobiont en_US
dc.subject Cladonia en_US
dc.subject Ramalina en_US
dc.title Evolution and Expression of polyketide synthase gene in the lichen-forming fungal families Cladoniaceae and Ramalinaceae en_US
dc.degree.discipline Biological Sciences en_US
dc.contributor.examiningcommittee Hausner, Georg (Microbiology) Sorensen, John L. (Chemistry) Weihrauch, Dirk (Biological Sciences) Lawrey, James D. (Environmental Science and Policy, George Mason University, Virginia) en_US
dc.degree.level Doctor of Philosophy (Ph.D.) en_US
dc.description.note February 2014 en_US

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