Date of Graduation
Neotyphodium lolii is a fungal endophyte of perennial ryegrass (Lolium perenne). Like related endophytes of other grasses, it increases the grass host's fitness. Endophyte-infected grasses have greater resistance to biotic and abiotic stress, and thus are highly competitive. However, the endophytes also produce toxins that cause toxicoses in grazing animals. N. lolii produces a large amount of lolitrems, which are thought to cause ryegrass staggers in mammals. The fungus also produces a smaller amount of a highly toxic ergopeptine ergovaline. In this dissertation, I have characterized, sequenced and surveyed the distribution of peptide synthetase gene IpsA that is required for biosynthesis of ergovaline in N. lolii . The lpsA gene encodes lysergyl peptide synthetase 1 (LPS1) catalyzing a late step of the ergovaline biosynthesis. The lpsA coding sequence is 10413 nucleotides in length. The deduced protein contains three amino acid-activating modules and four condensation (C) domains. The lpsA gene also contains two introns, which are rare in peptide synthetase genes. Intron 1 is 76 nucleotides located between the 5â€² C domain and the adenylation (A) domain of the first module, while intron 2 is 74 nucleotides long and located between the second C domain and the third A domain. Interestingly, the only other reported lysergyl peptide synthetase gene cpps1 of Claviceps purpurea required for ergotamine biosynthesis is proposed to contain only one intron, three amino acid-activating modules and three C domains. The distribution of lpsA homologues was surveyed in some fungi of the Clavicipitaceae closely related to N. lolii and in some morning glory plants (the Convolvulaceae family), which also contain ergot alkaloids. The lpsA homologues were detected only in the ergopeptine-producing relatives but not in the non-producers. Some relatives were found to contain polymorphisms of the lpsA homologues. Ergot alkaloids have been detected by HPLC in two species of the morning glories used in this study, Ipomoea violacea and I. alba . Southern hybridization with probe derived from the lysergyl peptide synthetase gene showed positive results only with I. alba DNA.
Damrongkool, Prapassorn, "Sequence and distribution of the Neotyphodium lolii peptide synthetase gene IpsA." (2003). Graduate Theses, Dissertations, and Problem Reports. 8711.