Adhesins -- do they play a role in the Epichloë festucae association with perennial rye grass? : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Genetics at Massey University, Palmerston North, New Zealand

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Adhesins have been extensively studied and characterised in prokaryotes and yeast. It has been shown that these proteins are important in development, symbiosis and pathogenicity. However, less is known about the role adhesins play in filamentous fungi. Adhesin genes have been identified and functionally characterised in Metarhizium robertsii and recently studied in Beauveria bassiana. The insect pathogen M. robertsii has two adhesin genes, Mad1 and Mad2, which were shown to be important in insect adherence or plant adherence respectively. Epichloë festucae has two adhesins, adsA and adsB, homologous to Mad1 and Mad2 respectively. Bioinfomatic analysis of E. festucae adhesins showed that in Fl1 adsA and adsB are separated by 25 genes. Analysis of adsB illustrated that the second adhesin gene is restricted to the Hypocreomycetidae. Phylogenetic analysis confirmed that adsB and adsA group separately in filamentous fungi. In this study, deletion mutants of E. festucae adsA and adsB were used to determine if one or both adhesins played a role in establishment of the hyphal network in culture and in symbiotic association with L. perenne. Deletion of adsA did not alter the growth of the hyphae in culture or in planta. Although, the growth of the adsB mutant in culture was not affected the growth in planta was different to that seen in wild-­-type associations. Mild whole plant stunting and colonisation of the large vascular bundles indicates that adsB plays a role in the early development of the symbiotic association. In contrast to M. robertsii where only Mad2 confers adherence of yeast to onion epidermal tissue, both E. festucae adsA and adsB confer adherence. The attachment of yeast cells expressing adsA, suggests that adsA does play a role in the symbiotic association. Physical attachment of the hyphae to host cells was not abolished when either adsA or adsB were deleted in E. festucae, suggesting gene redundancy in regards to physical attachment to the host tissue. This work provides insight into the role adhesins play in the symbiotic association of E. festucae and L. perenne.
Epichloë festucae, Genetics, Lolium perenne, Cell adhesion molecules, Research Subject Categories::NATURAL SCIENCES::Biology::Cell and molecular biology::Genetics