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Title: ISOLATION AND CHARACTERIZATION OF GAEUMANNOMYCES GRAMINIS VAR. GRAMINIS MELANIN MUTANTS

Author
item FREDERICK, B - MONTANA STATE UNIVERSITY
item CAESAR-TONTHAT, T - MONTANA STATE UNIVERSITY
item Wheeler, Michael - Mike
item SHEEHAN, K - MONTANA STATE UNIVERSITY
item EDENS, W - MONTANA STATE UNIVERSITY
item HENSON, J - MONTANA STATE UNIVERSITY

Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The plant pathogenic fungus Gaeumannomyces graminis var. graminis produces 1,8-dihydroxynaphthalene (DHN) melanin in its cell walls. We isolated two G. graminis mutants from a normally melanized wild type and they were affected in their melanin biosynthesis. One of these mutants was unable to synthesize DHN-melanin and appeared to be defective in the reductase that catalyzes the conversion of 1,3,8-trihydroxynaphthalene to vermelone, a step in the melanin pathway. The other mutant synthesized an excess of DHN melanin. Hyphae of the wild type and the heavily melanized mutant were more water repellent and more resistant to lytic enzymes, benomyl, restrictive temperature, and ultraviolet light than the non-melanized mutant, which also autolysed more readily. However, the non-melanized mutant was not more sensitive to heavy metal than the melanized strains. In addition, the non-melanized mutant was unaltered in pathogenicity to rice, whereas the heavily melanized mutant was less pathogenic. The heavily melanized mutant produced less extracellular lytic enzymes than the wild-type and the non-melanized mutant, which may explain its reduced virulence.

Technical Abstract: Gaeumannomyces graminis var. graminis is a filamentous ascomycete that produces 1,8-dihydroxynaphthalene (DHN) melanin in its hyphal and hyphopodial cell walls. We isolated G. graminis mutants that were affected in their melanin biosynthesis. One of these mutants was unable to synthesize DHN-melanin and because it accumulated 2-hydroxyjuglone, a DHN melanin pathway shunt product, this mutant is most likely to be defective in the reductase that catalyzes the conversion of 1,3,8- trihydroxynaphthalene to vermelone, the penultimate reaction in DHN synthesis. Genetic crosses with our wild-type strain indicated that this trihydroxynaphthalene reductase deficiency was the result of a single mutation. Another mutant constitutively synthesized DHN melanin and genetic crosses with our wild-type strain suggested that this heavily melanized mutant had a single mutation responsible for its phenotype. This smutant produced more melanin than the wild-type strain as measured by Azur A binding to melanin. The wild type and constitutively melanized mutant hyphae were more hydrophobic and more resistant to lytic enzymes, benomyl, restrictive temperature, and ultraviolet light than the non-melanized mutant, which also autolysed more readily. However, the non-melanized mutant was not more sensitive to heavy metal than the melanized strains. In addition, the non-melanized mutant was unaltered in pathogenicity to rice, whereas the constitutively melanized mutant was less pathogenic. The constitutively melanized mutant produced less extracellular lytic enzymes than the wild-type and the non-melanized mutant, which may explain its reduced virulence.