Chen, Lei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 142-161). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Rhynchosporium commune is one of the most destructive pathogens of barley worldwide. It can cause crop yield losses of up to 40% in the UK and decrease in grain quality. Populations of R. commune can change rapidly, defeating new barley resistance (R) genes and fungicides after just a few seasons of their use. Fungicide use is one of the major modes of management of Rhynchosporium and is heavily relied on the agricultural industry. Fungicides that were effective in the past are no longer effective in controlling the disease and many are only effective when used in mixtures. Beyond the currently effective fungicides there is limited new chemistry available so there is a very real need for development in this area. In pathogenic fungi, the cell wall components play a key role in the establishment of pathogenesis. The cell wall forms the outer structure protecting the fungus from the host defence mechanisms. It is involved in initiating the direct contact with the host cells by adhering to their surface. The fungal cell wall also contains important antigens and other compounds modulating host immune responses. R. commune germinated conidia and interaction transcriptome sequencing generated a list of over 30 different cell wall proteins (CWPs) potentially involved in pathogenicity. R. commune genome and interaction transcriptome sequencing provided further information about the extent of CWP families as well as a subset of genes expressed during barley colonisation by R. commune. The use of bioinformatic techniques allowed for the analysis of gene sequences. Putative cell wall associated genes were compared to the sequences from the fungal database via sequence similarity, sequence alignments 15 and conserved domain searches to better understand their function. Phylogenetic analysis also allowed us to understand the evolutionary relationship between R. commune genes and related genes in other organisms. Transcription profiling of R. commune CWPs during the development of infection helped to prioritise them for functional characterisation. Targeted gene disruption unfortunately did not yield mutants but has furthered our understanding of this technique in R. commune for future attempts. Functional complementation was successful however and allowed the uncovering of the function of RSA9. The results show that R. commune RSA9 functions as an allantoicase, an enzyme which breaks down purines as a source of nitrogen when conditions are nitrogen limited. The use of chemical cell wall inhibitors allowed us to better understand the role of carbohydrate cell wall components in R. commune fitness and virulence. Inhibition of cellulose production by DCB showed reduced growth, germination and pathogenicity of R. commune. Similar results were observed when beta-glucan synthesis was impaired; as inhibitor concentration increased, growth and germination of the fungus decreased. The composition of R. commune cell wall was also uncovered during this research. Techniques such as HPLC and FTIR eluded the composition of monosaccharides and polysaccharides respectively. In addition the structure of R. commune cell wall was observed by microscopy, namely TEM. This project revealed some much needed information on the R. commune cell wall and the relation of its components to fitness and virulence during infection of barley.

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The main aim of this project was to study Candida albicans cell wall biosynthesis in response to stress. The role of the MAPK, Ca2+/calcineurin and cAMP/PKA signal transduction pathways in regulating the C. albicans cell wall stress response was investigated. A library of mutants lacking receptors, signalling elements and transcription factors were screened for alterations in their ability to respond to a range of cell wall stressing agents, including CaCl2, Calcofluor White and caspofungin. Pretreatment of wild-type cells with CaCl2 and CFW, activates the Ca2+/calcineurin and PKC pathways, leading to an increase in chitin content, and reduced susceptibility to caspofungin. Although elevation of cell wall chitin content often resulted in decreased sensitivity to caspofungin, I show here that some strains with increased chitin levels remained sensitive to caspofungin. The results show that elevation of chitin is a common property of a range of mutants that are affected in coordinating cell wall stress pathways, but that multiple mechanisms are likely to operate in maintaining the robustness of the C. albicans cell wall. Some of the mutant strains of the MAPK, Ca2+/calcineurin and cAMP signalling pathways showed evidence of paradoxical growth, whereby less inhibition was achieved by higher concentrations of antifungal drug. The role of chitin-related genes and stress signalling pathways in regulating C. albicans paradoxical growth was also investigated. Based on these results, more detailed analyses were performed to investigate the correlations between sensitivity and resistance to caspofungin, in relation to paradoxical growth. The MAPK-Mkc1 and the calcineurin pathways played major roles in the paradoxical growth effect. There was a proportional relationship between echinocandin concentration and the chitin content of the cell wall although the chitin content did not continue to be upregulated by the highest echinocandin concentration. Different echinocandins, carbon source, cell morphology and medium composition influenced the extent of paradoxical growth effect. The existence of paradoxical growth in resistant strains such as Fks1 also highlights association of paradoxical growth with resistance mechanisms.

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Thesis (Ph. D.)--West Virginia University, 1998. / Title from document title page. "December 11, 1998." Document formatted into pages; contains ix, 94 p. : ill. (some col.) Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M. Sc.)--University of Canterbury, 2004. / Typescript (photocopy). "June 2004." Includes bibliographical references (leaves 105-113). Also available via the World Wide Web.

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