Chromatin-immunoprecipitation reveals the PnPf2 transcriptional network controlling effector-mediated virulence in a fungal pathogen of wheat

Abstract

The regulation of virulence in plant-pathogenic fungi has emerged as a key area of importance underlying host infections. Recent work has highlighted the role of transcription factors (TFs) that mediate the expression of virulence-associated genes. A prominent example is Pf2, a member of the Zn2Cys6 family of fungal TFs, where orthologues regulate the expression of genes linked to parasitism in several plant-pathogen lineages. These include PnPf2 which controls effector-gene expression in Parastagonospora nodorum, thereby determining the outcome of effector-triggered susceptibility on its host, wheat. PnPf2 is a promising target for disease suppression but the genomic targets, or whether other are regulators involved, remain unknown. This study used chromatin immunoprecipitation (ChIP-seq) and a mutagenesis analysis to investigate these components. Two distinct binding motifs connected to positive gene-regulation were characterised and genes directly targeted by PnPf2 were identified. These included genes encoding major effectors and other components associated with the P. nodorum pathogenic lifestyle, such as carbohydrate-active enzymes and nutrient assimilators. This supports a direct involvement of PnPf2 in coordinating virulence on wheat. Other TFs were also prominent PnPf2 targets, suggesting it also operates within a transcriptional network. Several TFs were therefore functionally investigated in connection to fungal virulence. Distinct metabolic and developmental roles were evident for the newly characterised PnPro1, PnAda1, PnEbr1 and the carbon-catabolite repressor PnCreA. Overall, the results uphold PnPf2 as the central transcriptional regulator orchestrating genes that contribute to virulence on wheat and provide mechanistic insight into how this occurs.

Regulation of effector gene expression as concerted waves in Leptosphaeria maculans: a two‐player game

“…In Parastagonospora nodorum , PnPf2 positively regulates two necrotrophic effector genes, SnToxA and SnTox3 , and the ortholog of SnToxA , ToxA , is regulated by PtrPf2 in Pyrenophora tritici‐repentis (Rybak et al ., 2017). A transcriptomic analysis comparing the WT and the PnPf2 mutant during axenic culture and infection of wheat revealed the involvement of PnPf2 in the regulation of 12 effector genes and genes associated with plant cell‐wall degradation and nutrient assimilation (Jones et al ., 2019), and promoters of effector genes were among the direct targets of PnPf2 as identified via a ChIP‐Seq analysis (John et al ., 2022a).…”