Transcription factor RFX1 is critical for maintenance of chromosome integrity in Fusarium graminearum

Abstract

The survival of cellular organisms depends on the faithful replication and transmission of DNA. Regulatory Factor X (RFX) transcription factors are well conserved in animals and fungi, but their functions are diverse, ranging from the DNA-damage response to ciliary gene regulation. We investigated the role of the sole RFX transcription factor, RFX1, in the plant-pathogenic fungus F. graminearum. Deletion of rfx1 resulted in multiple defects in hyphal growth, conidiation, virulence, and sexual development. Deletion mutants of rfx1 were more sensitive to various types of DNA damage than the wild-type strain. Septum formation was inhibited and micronuclei were produced in the rfx1 deletion mutants. The results of the neutral comet assay demonstrated that disruption of rfx1 function caused spontaneous DNA double-strand breaks (DSBs). Transcript levels of genes involved in DNA DSB repair were up-regulated in the rfx1 deletion mutants. DNA DSBs produced micronuclei and delayed septum formation in F. graminearum. GFP-tagged RFX1 localized in nuclei and exhibited high expression levels in growing hyphae and conidiophores, where nuclear division was actively occurring. RNA-sequencing-based transcriptomic analysis revealed that RFX1 suppressed the expression of many genes, including those required for the repair of DNA damage. Taken together, these findings indicate that the transcriptional repressor rfx1 performs crucial roles during normal cell growth by maintaining genome integrity.