Sorting F. graminearum core effector candidates shows multiple fungal proteins that target the wheat cell nucleus during Fusarium Head Blight

Effectors are small molecules secreted by microbial pathogens that disrupt host basal functioning and responses during infection by targeting various plant susceptibility factors. This study reports a candidate selection approach for identifying novel, potential plant nuclear localized effectors from Fusarium graminearum secretory proteins. From a dataset of core secretory proteins conserved across several Fusarium strains, candidates were selected based on predicted nuclear localization, structural characteristics, and expression profiles during infection. Transient expression in Nicotiana benthamiana confirmed accumulation in the plant nucleus, that were further confirmed in wheat protoplasts. One of these proteins was selected for yeast two-hybrid (Y2H) screening to identify wheat protein targets, using a Fusarium-infected wheat spike cDNA library specifically generated for this study. The screening identified a high confident interaction with a nuclear-localized wheat beta-amylase 2. The structural modeling of the protein complex between beta-amylase 2 and the putative effector was used to predict interacting amino acid residues and informed a deletion analysis to disrupt the interaction. This research identifies a Fusarium graminearum secretory core protein that interacts with a conserved wheat beta-amylase 2, showcasing a method to select pathogenicity factors conserved across multiple pathogens and host plants, with implications for developing broad-spectrum resistance strategies.