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Characterization and molecular genetic complementation of mutants affecting dimorphism in the fungus ustilago maydis
Abstract:
Ustilago maydis, the causal agent of corn smut disease, displays dimorphic growth in which it alternates between a unicellular, nonpathogenic yeast-like form and a dikaryotic, pathogenic filamentous form. Previously, a constitutively filamentous haploid mutant was obtained. Complementation of this mutant led to the isolation of the gene encoding adenylate cyclase, uac1. Secondary mutagenesis of a uac1 disruption strain allowed the isolation of a large number of suppressor mutants, termed ubc, for Ustilago bypass of cyclase, lacking the filamentous phenotype. Analysis of one of these suppressor mutants previously led to the identification of the ubc1 gene, encoding the regulatory subunit of cAMP-dependent protein kinase. In this report we describe the isolation of cosmids containing three new ubc genes, termed ubc2, ubc3, and ubc4. We also describe the morphology of the ubc2, ubc3, and ubc4 mutants in a uac1- background as well as in a background with a functional uac1 gene. In addition, we describe several mutant strains not complemented with any of the genes currently in hand and that are thus presumed to possess mutations in additional ubc genes. Copyright 1998 Academic Press.
Insights
Researchers identified new genes (ubc2, ubc3, ubc4) in Ustilago maydis that bypass the need for adenylate cyclase (uac1), controlling its pathogenic filamentous growth. This advances understanding of fungal dimorphism.
Area of Science:
- Mycology
- Plant Pathology
- Molecular Genetics
Background:
- Ustilago maydis exhibits dimorphic growth, switching between yeast and filamentous forms.
- This dimorphism is crucial for its pathogenicity as the causal agent of corn smut disease.
- Previous work identified the adenylate cyclase gene (uac1) and a suppressor mutant gene (ubc1).
Purpose of the Study:
- To identify novel genes involved in regulating Ustilago maydis dimorphic growth.
- To characterize new suppressor of cyclase (ubc) genes, specifically ubc2, ubc3, and ubc4.
- To investigate the role of these new ubc genes in both uac1- and uac1+ backgrounds.
Main Methods:
- Isolation of cosmids containing new ubc genes.
- Genetic analysis of ubc2, ubc3, and ubc4 mutants.
- Morphological characterization of mutant strains in different genetic backgrounds.
Main Results:
- Cosmids containing three new suppressor of cyclase genes (ubc2, ubc3, ubc4) were isolated.
- The morphology of ubc2, ubc3, and ubc4 mutants was described in uac1- and uac1+ strains.
- Several additional uncharacterized suppressor mutant strains were identified.
Conclusions:
- The study identified new genes (ubc2, ubc3, ubc4) that bypass the requirement for adenylate cyclase in Ustilago maydis.
- These findings contribute to understanding the complex genetic regulation of fungal dimorphism and pathogenicity.
- Further research is needed to characterize additional identified suppressor mutants.