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Title: Transcriptome analysis of a Ustilago maydis ust1 deletion mutant uncovers involvement of laccase and polyketide synthase genes in spore development

Author
item ISLAMOVIC, EMIR - University Of Georgia
item GARCIA-PEDRAJAS, MARIA - Ihsm-Uma-csic, Estación Experimental “la Mayora”
item CHACKO, NADIA - University Of Georgia
item ANDREWS, DAVID - University Of Georgia
item COVERT, SARAH - University Of Georgia
item Gold, Scott

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2014
Publication Date: 1/3/2015
Citation: Islamovic, E., Garcia-Pedrajas, M.D., Chacko, N., Andrews, D.L., Covert, S.F., Gold, S.E. 2015. Transcriptome analysis of a Ustilago maydis ust1 deletion mutant uncovers involvement of laccase and polyketide synthase genes in spore development. Molecular Plant-Microbe Interactions. 28(1):42-54.

Interpretive Summary: Previously, deletion of a fungal specific transcription factor encoding gene (ust1) generated a mutant strain that produces spore-like structures, normally only seen in plants. Here the authors examined a comparison of in vitro gene expression in the spore producing ust1 mutant versus in wild type. Among the several hundred genes differentially expressed were two (pks1 and lac1) that were hypothesized to be involved in melanin pigment production. Deletion of these genes reduced pigment production in vitro and in genuine teliospores produced in plants. The lac1 gene appeared to play an important role in virulence to seedlings and marginally reduced spore pigmentation. The pks1 gene dramatically reduced the production of teliospores and those produced were completely lacking melanization.

Technical Abstract: Ustilago maydis, causal agent of corn smut disease, is a dimorphic fungus alternating between a saprobic budding haploid, and an obligate pathogenic filamentous dikaryon. Maize responds to U. maydis colonization by producing tumorous structures, and only within these does the fungus sporulate, producing melanized sexual teliospores. Previously we identified Ust1, an APSES transcription factor, whose deletion led to filamentous haploid growth and the production of highly pigmented teliospore-like structures in culture. In this study, we analyzed the transcriptome of a ust1 deletion mutant and functionally characterized two highly up- regulated genes with potential roles in melanin biosynthesis, um05361, encoding a putative laccase (lac1) and um06414 encoding a polyketide synthase (pks1). The lac1 mutant strains showed dramatically reduced virulence on maize seedlings and fewer, less pigmented teliospores in adult plants. The pks1 mutant was unaffected in seedling virulence, but adult plant tumors generated hyaline, non-melanized teliospores. Thus, while pks1 appeared to be restricted to the synthesis of melanin, lac1 showed a broader role in virulence. In conclusion, the ust1 deletion mutant provided an in vitro model for sporulation in U. maydis, and functional analysis supports the efficacy of this in vitro mutant analysis for identification of genes involved in in planta teliosporogenesis.