MYT3, A Myb-Like Transcription Factor, Affects Fungal Development and Pathogenicity of Fusarium graminearum

We previously characterized members of the Myb protein family, MYT1 and MYT2, in Fusarium graminearum . MYT1 and MYT2 are involved in female fertility and perithecium size, respectively. To expand knowledge of Myb proteins in F. graminearum , in this study, we characterized the functions of the MYT3 gene, which encodes a putative Myb-like transcription factor containing two Myb DNA-binding domains and is conserved in the subphylum Pezizomycotina of Ascomycota. MYT3 proteins were localized in nuclei during most developmental stages, suggesting the role of MYT3 as a transcriptional regulator. Deletion of MYT3 resulted in impairment of conidiation, germination, and vegetative growth compared to the wild type, whereas complementation of MYT3 restored the wild-type phenotype. Additionally, the Δ myt3 strain grew poorly on nitrogen-limited media; however, the mutant grew robustly on minimal media supplemented with ammonium. Moreover, expression level of nitrate reductase gene in the Δ myt3 strain was decreased in comparison to the wild type and complemented strain. On flowering wheat heads, the Δ myt3 strain exhibited reduced pathogenicity, which corresponded with significant reductions in trichothecene production and transcript levels of trichothecene biosynthetic genes. When the mutant was selfed, mated as a female, or mated as a male for sexual development, perithecia were not observed on the cultures, indicating that the Δ myt3 strain lost both male and female fertility. Taken together, these results demonstrate that MYT3 is required for pathogenesis and sexual development in F. graminearum , and will provide a robust foundation to establish the regulatory networks for all Myb-like proteins in F. graminearum .