Biology subjects

Verdonk, C. J.

Publications and source records attributed to Verdonk, C. J..

3 recordsLinked to original sources

bioRxiv2026

Major effector loss reveals compensatory pathogenicity networks in a necrotrophic wheat pathogen

Necrotrophic effectors (NEs) are key determinants of virulence in the necrotrophic fungal pathogen Parastagonospora nodorum that causes septoria nodorum blotch of wheat. However, targeted removal of three important NEs SnToxA, SnTox1, and SnTox3 in the mutant{Delta} toxa13 previously revealed a redundancy mechanism is triggered, whereby pathogenicity on wheat is maintained. In this study, we investigated the gene regulatory profile underpinning this phenomenon and discover that virulence is not dependent on a fixed set of dominant effectors but instead arises from a flexible, epistatic compensatory network. Although host transcriptional responses to the P. nodorum wildtype SN15 and{Delta} toxa13 infection remained largely conserved, consistent with an overlapping disease-susceptibility pathway, a significant upregulation of candidate effector genes was observed in{Delta} toxa13. This included the recently characterised NE SnTox267, and several other candidate effectors able to induce necrosis in the non-host Nicotiana benthamiana, each carrying a predicted structural fold conserved across other pathogens. We therefore provide further direct evidence that virulence is maintained in P. nodorum lacking three NEs by an epistatic and compensatory effector network, underpinned by changes in pathogen gene expression. Targeting conserved effector-mediated virulence mechanisms rather than individual host-specific gene-for-gene interactions may provide a more tractable route to host resistance.

molecular biology↗

bioRxiv2026

The bZIP transcription factor PnAda1 functions as a regulator of virulence, fungicide tolerance and necrotrophy in the wheat pathogen Parastagonospora nodorum

Ada1 (All Development Altered-1) is a conserved but poorly characterised basic leucine zipper (bZIP) transcription factor found throughout filamentous fungi. In the wheat pathogen Parastagonospora nodorum, PnAda1 is required for full virulence and is transcriptionally associated with the virulence regulator PnPf2, but its biological functions remain unclear. Here, we combined comparative RNA sequencing with targeted phenotypic analyses to define the role of PnAda1 during vegetative growth and host infection. Deletion of PnAda1 did not abolish pathogenicity but delayed disease progression, with the PnAda1-deletion mutant transcriptome at 7 days post-inoculation resembling that of the wildtype SN15 at 3 days. This developmental delay was associated with impaired activation of early infection-associated genes, including putative carbohydrate-active enzymes, proteases, transporters and other host-colonisation factors. In contrast, expression of major necrotrophic effector genes was not reduced and instead remained elevated during later stages of infection, indicating that PnAda1 is required for the timely progression of infection-associated transcriptional regulation rather than direct activation of effector genes. Beyond virulence, transcriptomic and phenotypic analyses revealed roles for PnAda1 in nitrogen assimilation, carbon utilisation, abiotic stress responses and fungicide sensitivity. Notably, PnAda1 deletion increased sensitivity to succinate dehydrogenase inhibitor fungicides and reduced expression of succinate dehydrogenase subunit genes. Collectively, our findings identify PnAda1 as a broad regulator of developmental and infection-associated transitions in P. nodorum and expand current understanding of the transcriptional network underlying virulence, metabolism and stress adaptation in an important fungal wheat pathogen.

molecular biology↗

bioRxiv2025

A conserved fungal transcription factor domain drives protein-protein interactions and necrotrophic effector-mediated virulence in Parastagonospora nodorum

The fungal pathogen Parastagonospora nodorum utilises necrotrophic effectors (NEs) to cause chlorosis and necrosis on wheat. NE expression is mediated by an assortment of transcription factors (TF), the most well-characterised of which is PnPf2. Orthologues of PnPf2 regulate virulence in phytopathogenic fungi across the Ascomycete fungal lineage, yet their protein architecture remains functionally uncharacterised. These orthologues are characterised by the archetypal N-terminal Zn2Cys6 zinc-finger DNA-binding domain (DBD), a conserved yet poorly characterised middle-homology region (MHR) and a C-terminal disordered region. We investigated the role of each of the three domains through PnPf2 truncation mutants in situ. This revealed the conserved MHR of PnPf2 is required for the development of disease symptoms on wheat, but also that the C-terminal disordered region in-part modulates NE expression. Domain-interaction analysis through yeast-2-hybrid (Y2H) screening reveals PnPf2 forms a homodimer mediated by the MHR, indicating its importance mediating protein-protein interactions. Using the MHR as a bait in library-scale protein-protein interaction Y2H assays, we identified the COP9-signalosome protein PnCsn6 as a key interaction partner. PnCsn6 is essential for disease symptoms during P. nodorum infection on wheat, including NE expression. Our study presents the first domain-level functional investigation this virulence-regulating TF orthologue, the results of which underpin the essential role of the MHR in driving protein-protein interactions and effector regulation. It also reveals an essential protein-signalling pathway with which PnPf2 directly interacts and shares regulatory control of virulence.

molecular biology↗