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Gaeumannomyces graminis var. tritici is the aetiologic agent of take-all disease of wheat and barley. Heavily-melanized variants of a lightly pigmented, virulent wild-type strain were isolated and characterized. These variants were phenotypically similar to Phialophora sp., the proposed anamorph of Gaeumannomyces graminis var. tritici. Unlike the wild-type G. graminis strain, Phialophora-like variants produced conidia and lost their ability to reproduce sexually after serial transfer. Some ascospores from initial self-crosses of the Phialophora-like variants regained the G. graminis phenotype, and these derivatives could again produce Phialophora-like variants. As with Phialophora isolates from the field, Phialophora-like variants produced in this study were non-pathogenic and produced less extracellular protein.
Recently we cloned and characterized three laccase genes from Gaeumannomyces graminis var. tritici, an important pathogen of wheat. Here we report cloning and characterization of two laccase genes from G. graminis var. graminis, a weak pathogen of rice and turf grasses. LAC1 and LAC2 genes were present in both varieties of the fungus. The genes were 94–95% identical, and intron positions were conserved between the two varieties. Our data demonstrated that laccases might be useful for phylogenetic studies to detect fine differences between G. graminis subspecies, varieties, or strains of the fungus that cannot be detected by traditional sequencing of 18S rRNA genes or ITS regions. We previously characterized two G. graminis var. graminis melanin mutants with altered lytic enzyme secretion patterns. Here we demonstrate altered transcription patterns of laccase genes between the two varieties and between the wild type and melanin mutants of G. graminis var. graminis. Transcription of LAC2 was downregulated in the over-melanized mutant as compared to wild-type G.graminis var. graminis and the unmelanized mutant, whereas transcription of LAC1 in planta was up-regulated in the over-melanized mutant, as compared to the wild type and the unmelanized mutant. In the unmelanized mutant transcription of both genes was similar to that observed in the wild type.
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