Date of Award:

5-1-2000

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Anne J. Anderson

Committee

Anne J. Anderson

Committee

Joseph K.-K. Li

Committee

Donald W. Roberts

Committee

Lance C. Seefeldt

Committee

Jon Y. Takemoto

Committee

Bradley R. Kropp

Abstract

A fungal isolate present as a seed endophyte caused disease in wheat and other cereals when grown under stressed conditions. The isolate was identified as a member of the Asian clade of the Gibberella fujikuroi species complex in the genus Fusarium, members of which are known as plant pathogens and producers of mycotoxins. The closest relative to the fungus was Fusarium proliferatum, although none of the previously described species was identical in all morphological and molecular phylogenetic characters. At least six laccase isozymes were detected in mycelial extracts or from extracellular culture filtrates of the Fusarium-wheat isolate. A novel observation was their production during carbon and/or nitrogen limitation in the growth media. Extraction of the RNA from mycelia grown to stationary phase in low carbon culture followed by RT-PCR showed that there was transcription from four different putative laccase genes initially identified as sequences from the fungal genome by PCR. The production of laccase isozymes in low carbon- and low nitrogen-cultures was a common feature of seven other Fusarium species selected from within the G. fujikuroi complex and another phylogenetically distant wheat pathogen, F. culmorum. Probes derived from the four putative laccase clones from the Fusarium-wheat isolate revealed polymorphisms in Southern analyses of enzyme-restricted genomic DNAs. The RFLP patterns distinguished each of the Fusarium strains, including the five different F. proliferatum isolates examined. These findings suggest that laccase production may be a common feature of plant-associated Fusarium and that the polymorphisms in laccases at the protein and gene levels may offer a novel method for strain identification.

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