DescriptionNearly all plants engage in some form of symbiosis with fungi. An association that is of broad significance in turf is the symbiosis between endophytic fungi of the genus Epichloë and cool season grasses. There has been longstanding interest in the relationship between turfgrass and their Epichloë endosymbionts as endophyte infection of turfgrass can result in increased plant vigor, and confer tolerance to biotic and abiotic stress. Thus the Epichloë-turfgrass interaction is a promising model for studies aimed at understanding beneficial symbiotic associations in general. Fine fescues are valued as low maintenance turf spp. The E. festucae infection of strong creeping red fescue (Festuca rubra) is important because the symbiosis protects the host plant against fungal phytopathogens. The phytopathogens cause the devastating dollar spot, and red thread diseases. Remarkably, no other Epichloë-turfgrass interaction has been reported to confer fungal disease resistance. The E. festucae-infected fescues also have insect resistance. No study to date has investigated the E. festucae-F. rubra mutualism. The goal of this thesis was to use SOLiD-SAGE transcriptome analysis to identify candidate genes that may be important in the endophyte-grass symbiosis. The results of a high-throughput quantitative differential gene expression study between plants infected with E. festucae vis-à-vis endophyte-free plants, in addition to the discovery and functional characterization of a horizontally transferred gene into Epichloë spp., and the examination of E. festucae salicylate hydroxylase gene are detailed in this thesis. The findings from this dissertation are expected to contribute to the knowledge on fungal endosymbiont-plant mutualism.