Genome-informed trophic classification and functional characterization of virulence proteins from the maize tar spot pathogen Phyllachora maydis

Authors: ROGERS, ABIGAIL - Purdue University; Jaiswal, Namrata; ROGGENKAMP, EMILY - Michigan State University; Kim, Hye-Seon; MACCREADY, JOSHUA - Michigan State University; CHILVERS, MARTIN - Michigan State University; Scofield, Steven - Steve; IYER-PASCUZZI, ANJALI - Purdue University; Helm, Matthew

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2024
Publication Date: 5/8/2024
Citation: Rogers, A., Jaiswal, N., Roggenkamp, E., Kim, H., MacCready, J.S., Chilvers, M.I., Scofield, S.R., Iyer-Pascuzzi, A.S., Helm, M.D. 2024. Genome-informed trophic classification and functional characterization of virulence proteins from the maize tar spot pathogen Phyllachora maydis. Phytopathology. https://doi.org/10.1094/PHYTO-01-24-0037-R.
DOI: https://doi.org/10.1094/PHYTO-01-24-0037-R

Interpretive Summary: Tar spot is one of the most important diseases of maize (corn) cause by P. maydis. Though this fungal pathogen is considered one of the most economically important diseases of maize, yet the exact steps taken by the pathogen to cause disease are not known. In this study, we use fungal genomic sequences and gene expression data to predict the trophic lifestyle of P.maydis and characterized virulent factors (effectors) secreted by this pathogen to host cells. Our analyses showed that this fungal pathogen encodes predicted Carbohydrate-active enzymes which is consistent with that of biotrophs. Further we selected eighteen candidate effectors proteins on the basis of their expression during pathogenicity to characterize their role in host basal immune suppression and where they localize in host cell to function. We used transient expression system using Nicotiana bethamiana as a model plant and found that most of the effector proteins localize to nucleus and cytoplasm of N. bethamiana. Importantly, three candidate effectors consistently suppress chitin-iduced reactive oxygen species production in a manner dependent on their subcellular localization. Collectively, our results presented herein provide valuable insights into the predicted trophic lifestyle and putative functions of effectors from P. maydis and will likely stimulate continued research aimed at elucidating the molecular and cellular mechanisms used by this fungal pathogen to induce tar spot disease.

Technical Abstract: Phyllachora maydis is an ascomycete foliar fungal pathogen and the causal agent of tar spot disease in maize. Though this fungal pathogen is considered one of the most economically important foliar diseases of maize, our general knowledge regarding the trophic classification and molecular virulence factors remains limited. Here, we utilized a genome-informed approach to predict the trophic lifestyle of P. maydis and functionally characterized a subset of candidate effectors from this fungal pathogen. Our analyses revealed that this fungal pathogen encodes predicted Carbohydrate-active enzymes (CAZymes) consistent with that of biotrophs (monomertrophs). To further investigate fungal pathogenicity, we selected eighteen candidate virulence (effector) proteins that were previously shown to be expressed during disease development. We assessed whether these putative effectors share structural homology with other characterized fungal effectors as well as determined whether any suppress immune responses. Using AlphaFold2 and Foldseek, we showed one candidate effector, PM02_g1115, adopts a predicted protein structure similar to that of PevD1, an effector from Verticillium dahlia. Furthermore, transient expression of candidate effector-fluorescent protein fusions in Nicotiana benthamiana revealed that most of the effector proteins localize to both the nucleus and the cytosol. Importantly, three candidate effectors consistently attenuated chitin-mediated reactive oxygen species production in a manner dependent on their subcellular localization. Collectively, our results presented herein provide valuable insights into the predicted trophic lifestyle and putative functions of effectors from P. maydis and will likely stimulate continued research aimed at elucidating the molecular and cellular mechanisms used by this fungal pathogen to induce tar spot disease.