<i>UvCom1</i> Is an Important Regulator Required for Development and Infection in the Rice False Smut Fungus <i>Ustilaginoidea virens</i>

Abstract

<i>Ustilaginoidea virens</i> is an economically important biotrophic fungal pathogen that causes rice false smut worldwide. However, the regulatory mechanisms of smut ball formation under <i>U. virens</i> infection remain unclear. Here, we identified an important transcription factor, <i>UvCom1</i>, from this pathogen, which regulates the formation of smut balls on rice spikelets. UvCom1 contains two conserved internal repeat 1 (RPT) domains and is found only in fungi, with specific conservation in species of Basidiomycetes and Ascomycetes. UvCom1 protein N- or C-terminal fusion vectors both showed transactivation activity in yeast. Deletion of <i>UvCom1</i> significantly affected the vegetative growth and conidiation of <i>U. virens</i>. <i>UvCom1</i> negatively regulated the responses to oxidative, osmotic, and cell wall stresses. Remarkably, <i>UvCom1</i> was found to be essential for the formation of rice smut balls, and <i>UvCom1</i> deletion mutants lost the ability to stably utilize nutrients from the rice host. <i>UvCom1</i> was also highly expressed at the mycelial expansion stage. Transcriptomic analysis and quantitative real-time PCR revealed that <i>UvCom1</i> could affect the expression of genes significantly enriched in transmembrane transport. This study demonstrates that <i>UvCom1</i> is a key transcription factor governing smut ball formation of this biotrophic fungus.