Unh1, an Ustilago maydis Ndt80-like protein, controls completion of tumor maturation, teliospore development, and meiosis

In this study, Ustilago maydis Ndt80 homolog one, unh1, of the obligate sexual pathogen U. maydis, is described. Unh1 is the sole Ndt80-like DNA-binding protein in U. maydis. In this model basidiomycete, Unh1 plays a role in sexual development, influencing tumor maturation, teliospore development and subsequent meiotic completion. Teliospore formation was reduced in deletion mutants, and those that did form had unpigmented, hyaline cell walls, and germinated without completing meiosis. Constitutively expressing unh1 in haploid cells resulted in abnormal pigmentation, when grown in both potato dextrose broth and minimal medium, suggesting that pigmentation may be triggered by unh1 in U. maydis. The function of Unh1 in sexual development and pigment production depends on the presence of the Ndt80-like DNA-binding domain, identified within Unh1. In the absence of this domain, or when the binding domain was altered with targeted amino acid changes, ectopic expression of Unh1 failed to complement the unh1 deletion with regards to pigment production and sexual development. An investigation of U. maydis genes with upstream motifs similar to Ndt80 recognition sequences revealed that some have altered transcript levels in Δunh1 strains. We propose that the first characterized Ndt80-like DNA-binding protein in a basidiomycete, Unh1, acts as a transcription factor that is required for teliospore maturation and the completion of meiosis in U. maydis.