Investigation of signalling involved in maintaining the mutually beneficial association between Epichloe festucae and perennial ryegrass : 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

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dc.contributor.authorEaton, Carla Jane
dc.date.accessioned2010-02-09T21:56:40Z
dc.date.availableNO_RESTRICTIONen_US
dc.date.available2010-02-09T21:56:40Z
dc.date.issued2009
dc.descriptionContent removed from thesis due to copyright restrictions: Eaton, C. J., I. Jourdain, et al. (2008). "Functional analysis of a fungal endophyte stress-activated MAP kinase." Current Genetics 53(3): 163-174. Scott, B. and C. J. Eaton (2008). "Role of reactive oxygen species in fungal cellular differentiations." Current Opinion in Microbiology 11(6): 488-493.en_US
dc.description.abstractIn the mutually beneficial association between the fungal endophyte Epichloƫ festucae and perennial ryegrass, fungal growth is highly regulated and coordinated with that of the host. This implies there must be signalling between the fungus and its host to maintain this close association. Recent work has shown a novel role for reactive oxygen species (ROS) in this symbiotic maintenance, with multiple components of the superoxideproducing NADPH oxidase (Nox) complex being essential for normal association. However, the mechanism by which the Nox complex is regulated is unclear. To identify potential regulators of the E. festucae Nox complex, comparisons were made with well-characterised mammalian systems. This search identified three candidate regulators: a stress activated MAP kinase, sakA, and the p21-activated kinases, pakA and pakB. To investigate if these genes were involved in symbiotic maintenance, replacement mutants were generated by homologous recombination. In culture analysis revealed that the ?sakA mutant was hypersensitive to a range of stresses, whereas the pak mutants were hypersensitive to cell wall stress-inducing agents and displayed altered growth and morphology. Examination of perennial ryegrass infected with these mutants revealed drastically altered plant interaction phenotypes for the ?sakA and ?pakA mutants in comparison to the wild-type strain. ?sakA-infected plants were stunted and displayed striking changes in development, with the base of tillers showing loss of anthocyanin pigmentation and disorganisation of host cells below the meristem, resulting in swollen bases. Plants infected with the ?pakA mutant were severely stunted, had no more than two tillers and senesced soon after planting. In contrast, plants infected with the ?pakB mutant were similar to wild-type, with only slight deregulation of growth in planta. Examination of ROS in culture revealed that ?sakA and ?pakA displayed elevated levels of both superoxide and hydrogen peroxide. ROS levels were also elevated around ?sakA hyphae in planta. These results support roles for SakA and PakA in Nox regulation. This work highlights the fine balance between mutualism and antagonism, and provides insight into the molecular basis for mutualism.en_US
dc.identifier.urihttp://hdl.handle.net/10179/1179
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectKinasesen_US
dc.subjectMutantsen_US
dc.subject.otherFields of Research::270000 Biological Sciences::270200 Geneticsen_US
dc.titleInvestigation of signalling involved in maintaining the mutually beneficial association between Epichloe festucae and perennial ryegrass : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Genetics at Massey University, Palmerston North, New Zealanden_US
dc.typeThesisen_US
massey.contributor.authorEaton, Carla Jane
thesis.degree.disciplineGeneticsen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophy (Ph. D.)en_US
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