Investigations of dothistromin gene expression in Dothistroma septosporum and the putative role of dothistromin toxin : a thesis presented in the partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Molecular Biology at Massey University, Palmerston North, New Zealand.

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dc.contributor.authorSchwelm, Arne
dc.date.accessioned2010-03-01T22:53:09Z
dc.date.available2010-03-01T22:53:09Z
dc.date.issued2007
dc.descriptionContent removed from thesis due to copyright restrictions: Schwelm, A., Barron, N. J., Zhang, S. & Bradshaw, R. E. (in press). Early expression of aflatoxin-like dothistromin genes in the forest pathogen Dothistroma septosporum.en_US
dc.description.abstractDothistroma septosporum causes pine needle blight, a foliar disease currently causing epidemics in the Northern hemisphere. D. septosporum synthesizes dothistromin, a mycotoxin similar in structure to the aflatoxin (AF) precursor versicolorin B. Orthologs of AF genes, required for the biosynthesis of dothistromin, have been identified along with others that are speculated to be involved in the same pathway. The dothistromin genes are located on a mini-chromosome in Dothistroma septosporum but, in contrast to AF genes, not in a continuous cluster. The aim of this study was to increase knowledge of the biological role of dothistromin, which was previously a suspected pathogenicity factor. To identify putative roles of dothistromin, the dothistromin gene expression was investigated and green fluorescence protein (GFP) reporter gene strains of D. septosporum were developed. Expression analyses of dothistromin genes revealed co-regulation. More surprisingly, dothistromin is produced at an early stage of growth and gene expression is highest during exponential growth. This is fundamentally different to the late exponential/stationary phase expression usually seen with secondary metabolites such as AF. Strains with a dothistromin gene (dotA) promoter-regulated GFP confirmed early expression of the toxin genes, even in spores and germtubes. Parallel studies with transformants containing a GFP-DotA fusion protein suggest spatial organization of dothistromin biosynthesis in intracellular vesicles. The early expression of dothistromin genes led to the hypotheses that dothistromin is either required in the early stage of the plant/fungi interaction, or for inhibiting the growth of competing fungi. Constitutive GFP strains helped to determine that dothistromin is not a pathogenicity factor. However, a putative role of dothistromin in competition with other fungi, including pine-colonizing species, was detected, supporting the second hypothesis. It was shown that dothistromin-producing strains appear to have a competitive advantage which is lacking in dothistromin-deficient strains. However, some competitors were not affected and have potential as biocontrol agents. In summary, this work has led to the discovery of an unusual pattern of regulation of a secondary metabolite, has made substantial progress in identifying the biological role of dothistromin, and has indicated potential for biocontrol of Dothistroma needle blight.en_US
dc.identifier.urihttp://hdl.handle.net/10179/1187
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectFungal gene expressionen_US
dc.subjectDothistroma septosporumen_US
dc.subjectDothistroma needle blighten_US
dc.subjectPinus radiata diseasesen_US
dc.subject.otherFields of Research::270000 Biological Sciences::270200 Genetics::270201 Gene expressionen_US
dc.titleInvestigations of dothistromin gene expression in Dothistroma septosporum and the putative role of dothistromin toxin : a thesis presented in the partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Molecular Biology at Massey University, Palmerston North, New Zealand.en_US
dc.typeThesisen_US
massey.contributor.authorSchwelm, Arne
thesis.degree.disciplineMolecular Biologyen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (Ph.D.)en_US
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