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

Abstract

Phyllachora maydisis an ascomycete foliar fungal pathogen and the causal agent of tar spot in maize. ThoughP. maydisis considered one of the most economically important foliar pathogens of maize, our general knowledge of the trophic lifestyle and functional role of effector proteins from this fungal pathogen remains limited. Here, we utilized a genome-informed approach to predict the trophic lifestyle ofP. maydisand functionally characterized a subset of candidate effectors from this fungal pathogen. Leveraging the most recentP. maydisgenome annotation and the CATAStrophy pipeline, we show this fungal pathogen encodes a predicted Carbohydrate-active enzymes (CAZymes) repertoire consistent with that of biotrophs (monomertrophs). To investigate fungal pathogenicity, we selected eighteen candidate effector proteins that were previously shown to be expressed during primary disease development. We assessed whether these putative effectors share predicted structural similarity with other characterized fungal effectors and determined whether any suppress plant immune responses. Using AlphaFold2 and Foldseek, we showed one candidate effector, PM02_g1115, adopts a predicted protein structure similar to that of an effector fromVerticillium dahlia. Furthermore, transient expression of candidate effector-fluorescent protein fusions inNicotiana benthamianarevealed that most effector proteins localize to both the nucleus and the cytosol. Importantly, three candidate effectors consistently attenuated chitin-mediated reactive oxygen species production inN. benthamiana. Collectively, these results presented herein provide valuable insights into the predicted trophic lifestyle and putative functions of effectors fromP. maydisand will likely stimulate continued research to elucidate the molecular mechanisms used byP. maydisto induce tar spot.