Activation of the Ustilagic Acid Biosynthesis Gene Cluster in Ustilago maydis by the C ₂ H ₂ Zinc Finger Transcription Factor Rua1

Abstract

The phytopathogenic basidiomycetous fungus Ustilago maydis secretes, under conditions of nitrogen starvation, large amounts of the biosurfactant ustilagic acid (UA). This secreted cellobiose glycolipid is toxic for many microorganisms and confers biocontrol activity to U. maydis. Recently, a large gene cluster that is responsible for UA biosynthesis was identified. Here, we show that expression of all cluster genes depends on Rua1, a nuclear protein of the C 2 H 2 zinc finger family, whose gene is located within the gene cluster. While deletion of rua1 results in complete loss of UA production, overexpression of rua1 promotes increased UA synthesis even in the presence of a good nitrogen source. Bioinformatic analysis allowed us to identify a conserved sequence element that is present in the promoters of all structural genes involved in UA biosynthesis. Deletion analysis of several promoters within the cluster revealed that this DNA element serves as an upstream activating sequence (UAS) and mediates Rua1-dependent expression. We used the yeast one-hybrid system to demonstrate specific recognition of this DNA element by Rua1. Introduction of nucleotide exchanges into the consensus sequence interfered with Rua1-dependent activation, suggesting that this sequence element acts as a direct binding site for Rua1.

The Ustilago maydis Nit2 Homolog Regulates Nitrogen Utilization and Is Required for Efficient Induction of Filamentous Growth

“…The biosynthetic genes are organized in gene clusters that have already been characterized (78). Recently, the transcriptional activator Rua1 has been shown to control the upregulation of the ustilagic acid gene cluster under nitrogenlimiting conditions (79). We also observed the formation of needle-shaped crystals that are reminiscent of ustilagic acid production after keeping both SG200 and Nit2-deficient sporidia for 4 days on nitrogen starvation medium (Fig.…”

“…The activation of the biosynthetic gene cluster has been shown to be mediated by the transcription factor Rua1, and it has been postulated that Rua1 is under the control of Nit2 (79). Our data suggest that glycolipid production is not under the control of Nit2 and may, therefore, be controlled by additional transcriptional inducers.…”

RNA-Seq Revealed Differences in Transcriptomes between 3ADON and 15ADON Populations of Fusarium graminearum In Vitro and In Planta

“…The function of the C2H2 zinc finger proteins in F . graminearum is unknown, but their roles have been studied in other fungi, such as calcium signaling in Aspergillus nidulans ( CrzA ) [72], regulation of biological processes (sexual development) ( SteA ) in Aspergillus [73], ustilagic acid biosynthesis ( Rua1 ) in Ustilago maydis [74]. Of the TF encoding genes characterized by Son et al [60] using deletion mutation, five genes (FGSG_00764 and FGSG_01298 with C2H2 zinc finger domain, FGSG_09286 and FGSG_10142 with bZIP domain, and FGSG_09871 with bromo domain) up-regulated in the 3ADON population were involved in either virulence or DON biosynthesis or both.…”

Chapter 10. Epigenetic Approaches to Natural Product Synthesis in Fungi

“…These pathway-specific transcription factors are required for synthesis of many SMs, including: gliotoxin (gliZ), 70 tricothecene (tri6), 71 aflatoxin/sterigmatocystin (aflR), 40,72 citrinin (ctnA), 73 aspyridone (apdR), 74,75 asperfuranone (afoA), 76 and ustilagic acid (rua1). 77 Characterization of the sterigmatocystin cluster transcription factor aflR led to the identification of a sequence-specific binding motif present in several copies within the promoter region of most sterigmatocystin cluster genes. 78 Removal of these cluster-specific transcription factors typically results in decreased expression of the entire cluster.…”