The candidate transcription factors PnAtfA, PnCrz1, and PnVf19 contribute to fungal morphogenesis, abiotic stress tolerance, and pathogenicity in the wheat pathogen Parastagonospora nodorum

The necrotrophic fungus Parastagonospora nodorum, the causal agent of wheat glume blotch, is responsible for substantial economic losses in many wheat-growing regions. Despite the high number of transcription factor (TF)-encoding genes in the genome of P. nodorum, very little is known about their regulatory functions. Here, we assessed the role of three TFs in the regulation of P. nodorum virulence on wheat. We identified encoded in the genome of P. nodorum PnAtfA, PnCrz1, and PnVf19, homologous candidate TFs to Schizosaccharomyces pombe Atf1, Saccharomyces cerevisiae CRZ1, and S. cerevisiae Msn2, respectively. Targeted gene replacement of each gene led to reduced mycelial vegetative growth and loss of pathogenicity on wheat. Deletion of PnAtfA resulted in phenotype alteration with ΔPnCrz1 deletion mutants displayed abnormal colony morphology characterized by dense hyphal branching and loss of aerial hyphae development, showing that both PnAtfA and PnCrz1 regulate fungal morphogenesis. Additionally, deletion of PnAtfA and PnVf19 genes abolished pycnidiospore production whereas ΔPnCrz1 produced fewer pycnidiospores compared to the wild type. Furthermore, ΔPnCrz1 and ΔPnVf19 deletion mutants demonstrated increased sensitivity to hydrogen peroxide showing their involvement in oxidative stress response. The ΔPnVf19 deletion mutants exhibited increased sensitivity to sodium chloride, suggesting that PnVf19 is essential for osmotic tolerance response. Taken together, these findings suggest that the selected candidate TFs play a key role in the fungal morphogenesis, sporulation, oxidative and osmotic stress tolerance response, and full virulence in P. nodorum.