|Karakkat, Brijesh -|
|Covert, Sarah -|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 13, 2013
Publication Date: December 13, 2013
Citation: Karakkat, B.B., Gold, S.E., Covert, S.F. 2013. Two members of the Ustilago maydis velvet family influence teliospore development and virulence on maize seedlings. Fungal Genetics and Biology. 61(2013):111-119. Interpretive Summary: Velvet protein genes have previously been analyzed in fungi of the phylum Ascomycota, where they play important roles in spore formation and other developmental processes. In this work, three velvet-like genes (umv1, umv2 and umv3) were identified and functionally analyzed in the corn smut pathogen, Ustilago maydis, and this therefore constitutes the first report of velvet gene function in a member of the other phylum of the higher fungi, the Basidiomycota. By using gene deletion mutant analysis for each of the umv genes it was determined by maize seedlings inoculation tests that umv1 was critical for disease development and spore production, umv2 was needed for the normal rate of disease development, while umv3 appeared dispensable having little or no observable impact. Additionally, none of the mutants showed altered morphological development in culture. These results indicate that two U. maydis velvet family members, umv1 and umv2, are important for normal teliospore development and disease progression in maize seedlings.
Technical Abstract: Members of the fungal-specific velvet protein family regulate sexual and asexual spore production in the Ascomycota. We predicted, therefore, that velvet homologs in the basidiomycetous plant pathogen Ustilago maydis would regulate sexual spore development, which is also associated with plant disease progression in this fungus. To test this hypothesis, we studied the function of three U. maydis velvet genes, umv1, umv2 and umv3. Using a gene replacement strategy, deletion mutants were made in all three genes in compatible haploid strains, and additionally for umv1 and umv2 in the solopathogenic strain, SG200. None of the mutants showed novel morphological phenotypes during yeast-like, in vitro growth. However, the delta umv1 mutants failed to induce galls or teliospores in maize. Chlorazol black E staining of leaves infected with delta umv1 dikaryons revealed that the delta umv1 hyphae did not proliferate normally and were blocked developmentally before teliospore formation. The delta umv2 mutants were able to induce galls and teliospores in maize, but were slow to do so and thus reduced in virulence. The delta umv3 mutants were not affected in teliospore formation or disease progression. Complementation of the delta umv1 and delta umv2 mutations in the SG200 background produced disease indices similar to those of SG200. These results indicate that two U. maydis velvet family members, umv1 and umv2, are important for normal teliospore development and disease progression in maize seedlings.