The fungal endophyte Epichloë festucae forms a largely mutualistic association with the ryegrass species Lolium perenne. E. festucae produces a range of bio-protective alkaloids that protect the host grass from herbivory by both mammals and insects. One such alkaloid, Lolitrem B, is a potent mycotoxin and the causative agent of ryegrass staggers in livestock. Ten genes required for biosynthesis of lolitrem B are encoded in the ltm gene cluster. The ltm genes are expressed in a plant-specific manner, with high levels of expression in planta and very low levels of expression in culture. The mechanism regulating ltm gene expression is unknown but it is predicted to involve signalling from the host plant. The ltmM gene was chosen for use in the investigation of ltm gene regulation because the flanking regions do not contain retrotransposon sequence, which surrounds much of the ltm gene cluster. To identify fungal genes involved in the plant-induced expression of ltmM, a mutagenesis and screening system was developed using a PltmM-gusA ‘knock-in’ construct to detect expression from the ltmM promoter. Agrobacterium tumefaciens-mediated T-DNA mutagenesis was used to create a set of mutants with random insertions in the genome. Mutants were then screened for altered PltmM-gusA expression, both in culture and in planta. Three mutants were identified with increased PltmM-gusA expression in culture, however, no mutants were identified with loss of PltmM-gusA expression in planta. This indicates that a mechanism of repression is involved in the plant-induced expression of ltmM, either directly or indirectly. TM mutants of interest were also observed for altered symbiosis phenotypes. Mutants were identified with reduced colonisation rates and altered hyphal growth in planta. Integration sites were identified for two colonisation mutants and the disrupted genes are predicted to be the CTP:cholinephosphate cytidylyltransferase (CCT) gene PCT1 and the mitogen-activated protein kinsase kinase (MAPKK) gene mkk2.
| Identifer | oai:union.ndltd.org:ADTP/269431 |
| Date | January 2008 |
| Creators | Brasell, Emma |
| Publisher | Massey University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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