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    How does Epichloë festucae avoid the host defence response? : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Genetics at Massey University, Palmerston North, New Zealand
    (Massey University, 2018) Noorifar, Nazanin
    Epichloë festucae is a filamentous fungus, which forms symbiotic associations with aerial tissues of Lolium and Festuca grass species. Chitin, a polymer of N-acetyl-Dglucosamine, is an important component of the fungal cell wall and a well-known pathogen associated molecular pattern (PAMP). Chitin promotes pathogen-triggered immunity (PTI) upon hydrolysis with plant chitinases and release of chitin oligomers. Therefore, to establish a stable and successful symbiosis, the endophyte needs to remain ‘hidden’ from the host immune system or actively suppress it. Confocal laser scanning microscopy (CLSM)-based analysis of leaf tissue infected with the E. festucae wild type strain and infiltrated with the chitin-specific molecular probe, WGA-Alexa Fluor-488, showed that only the septa of endophytic hyphae bound this probe while the entire cell wall was labelled in epiphyllous hyphae confirming previous observations that hyphal cell wall chitin is either masked or remodelled in endophytic hyphae. The aims of this project were (i) to test whether E. festucae LysM-containing proteins have a role in binding to or sequestering cell wall chitin oligomers and thereby preventing PAMPtriggered immunity and (ii) to analyse the composition of the cell wall of endophytic and epiphytic hyphae. An analysis of the E. festucae genome identified seven genes encoding proteins with LysM domains. Expression of two of these genes, lymA and lymB, increased in planta compared to in culture. Interestingly, both are divergently transcribed from chitinase encoding genes (chiA and chiB respectively), which also have increased expression in planta. Single gene deletion mutants of lymA, lymB, chiA and chiB as well as a double gene deletion ΔlymA/B were generated, and their plant interaction phenotype analysed. Plants infected with DlymA, DlymB or DchiA had the same plant-interaction phenotype as wild type whereas ΔchiB and ΔlymA/B mutants had defects in hyphal growth within the leaves. Analysis of hyphal cell wall structure using Chitin Binding Protein (CBP) and chitosan (CAP (Chitosan Affinity Protein) and OGA-488)-specific eGFP-based biosensors suggest that cell wall chitin is converted to chitosan in endophytic hyphae. This structural change is consistent with a lack of a defence response when E.festucae forms a mutualistic symbiotic association with L. perenne. Three E. festucae chitin deacetylase genes were identified (cdaA, cdaB and cdaC), and gene expression analysis showed cdaA expression is significantly increased in planta compare to in culture. Functional analysis of cdaA revealed that although plants infected with the ΔcdaA mutant had a similar whole plant interaction phenotype as wild type, they had an abnormal cellular phenotype. Patches of chitin were exposed along the endophytic hyphae confirming this mutant was unable to convert chitin to chitosan. However, hyphae in these plants still labelled with the chitosan biosensor OGA-488 demonstrating that despite the deletion of the cdaA, the hyphal cell wall of endophytic hyphae still contain chitosan suggesting that another chitin deacetylase, possibly CdaB has a redundant function in E.festucae. Collectively these results show that lymA, lymB and chiB are required for establishment of the symbiosis between E.festucae and L. perenne. In addition, this study shows that chitin is converted to chitosan in the hyphal cell wall of endophytic hyphae during the infection and colonisation of the host. The E. festucae chitin deacetylase gene cdaA is also essential for proper hyphal growth in planta and the symbiotic interaction.
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    The immunomodulatory role of lipoteichoic acid from probiotic bacteria : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biochemistry, Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
    (Massey University, 2011) Jöbsis, Carel Michael Hutchings
    Different probiotics provide different health benefits, and some of these may be explained by immunomodulatory activity. These immunomodulatory effects can vary between different probiotic strains and microbial-associated molecular patterns (MAMPs) may be responsible for this variation. One MAMP, lipoteichoic acid (LTA), is a macroamphiphile associated with the cell surface of gram positive bacteria. LTAs from different strains of bacteria have been shown to induce different immunomodulatory profiles. LTA was purified from three strains of lactic acid bacteria (LAB) that are known to elicit different immune responses, then analysed for immunomodulatory activity using human cell based assays. The activity of each LTA was shown to reflect elements of the immunomodulatory profile of the original strain. The structure of each LTA was determined using NMR (nuclear magnetic resonance spectroscopy). Structural differences found between the LTAs were compared to the differences in their immunomodulatory behaviours, showing that the differing structures may be responsible for strain-specific immune profiles. It has been previously shown that inactivation of the dltD gene in an established probiotic strain of LAB results in changes to the immune effects induced by the mutant bacterial cell compared to the wild type. This study has shown using NMR analysis that the structure of LTA isolated from this mutant strain is altered, reflecting the distinct immune profile of the mutant bacteria. LTAs from the three strains in this study were found to contain N-acetyl-glucosamine substituents, which have previously been found only on highly pro-inflammatory LTAs, e.g., those from Staphylococcus aureus. LTAs from the three strains were also shown to contain unsaturated fatty acids, which have so far been found in the LTAs of only LAB, including three other probiotic strains. These structural features may explain some of the immunomodulatory effects observed for these strains. It was found that isolated LTA may not be as effective at inducing immune responses as LTA on cells. Further exploration of potential interactions of LTA with other MAMPs, and other factors that may alter the presentation of LTA to immune cells in the case of intact cells is necessary to fully understand the role of LTA in immunomodulation.
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    A search for genetic factors influencing immune responses to a killed Mycobacterium avium subspecies paratuberculosis vaccine in Australian fine-wool merino sheep : thesis in fulfilment of the degree of Doctor of Philosophy in Animal Science, Institute of Veterinary, Animal and Biomedical Sciences, College of Sciences, Massey University
    (Massey University, 2007) Dukkipati, Venkata Sayoji Rao
    VSR Dukkipati (2007). A search for genetic factors influencing immune responses to Mycobacterium avium subspecies paratuberculosis. Doctoral thesis, Massey University, Palmerston North, New Zealand. A study was conducted to identify associations between genetic markers and immune responses in Australian fine-wool Merino sheep to a killed Mycobacterium avium subspecies paratuberculosis (Map) vaccine (GudairTM). Blood samples and immune response data (antibody and interferon gamma, IFN-gamma results) were obtained from 934 sheep from a longterm Map vaccination trial undertaken on three independent properties in New South Wales, Australia. Blood samples were genotyped for eight microsatellite markers that included four (DYMS1, OLADRW, OLADRB and SMHCC1) from the Ovar-Mhc region, two each from the SLC11A1 (OVINRA1 and OVINRA2) and IFN-gamma (o(IFN)gamma and OarKP6) gene regions. Vaccination with GudairTM induced strong antibody and IFN-gamma responses as early as two weeks post-vaccination. Between-property differences in magnitude and trend of immune responses, concomitant with season of vaccination and magnitude of natural infection prevalent in individual flocks, were evident. Immune responses in controls on all the three properties remained consistently low, except for slightly elevated IFN-gamma levels at a few time points in controls of properties 2 and 3, concomitant with exposure to natural infection. There were only 2 alleles and 3 genotypes for marker o(IFN)gamma but other loci exhibited extensive polymorphisms, the most occurring at OLADRW which had 42 alleles and 137 genotypes. Heterozygosities varied between 33% (OVINRA2) and 87% (SMHCC1), while polymorphic information contents ranged from 0.31 (o(IFN)gamma) to 0.88 (OLADRW). Genotypes at loci DYMS1, OLADRB, SMHCC1, OVINRA1 and o(IFN)gamma were in Hardy- Weinberg equilibrium (HWE), while those at OarKP6 were in HWE only when rare alleles (<1.0% frequency) were pooled with the closest size class. Departure from HWE, resulting from possible preferential amplification of alleles in heterozygotes, was evident at OLADRW and OVINRA2. Associations between immune responses and genetic polymorphisms at the marker loci were examined by analysing both genotypic and allelic affects. The study revealed several genotypes/alleles at different marker loci to be significantly associated with antibody and IFN-gamma responses to vaccination with GudairTM. However, the majority of those effects were inconsistent across the three properties. Based on significance and consistency in effects across the three properties, five genotypes (two at DYMS1 and one each at OLADRB, SMHCC1 and OVINRA1) and three alleles (one each at DYMS1, OLADRB and o(IFN)gamma) were considered either ‘probable’ or ‘most likely’ to be associated with low IFN-gamma responses, while a genotype at o(IFN)gamma was considered ‘most likely’ to influence high IFN-gamma responses. An allele at OarKP6 was considered ‘probable’ to be associated with low antibody responses to vaccination. Considering the significance of IFN-gamma responses in protection against Map, it is likely that the identified genotype/alleles influencing IFN-gamma responses to vaccination would also influence immune responses to natural Map infections. However, further studies need to be conducted to determine the role of these marker genotypes/alleles in protection against paratuberculosis under natural infection conditions. Key words: paratuberculosis, OJD, Johne’s disease, sheep, immune response, genetic markers, gene polymorphisms, MHC, SLC11A1, IFN-gamma