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.