A tomatinase-like enzyme acts as a virulence factor in the wheat pathogen Fusarium graminearum

During their interactions with plants, fungal pathogens employ large numbers of pathogenesis-associated molecules including secreted effectors and enzymes that can degrade various defence compounds. However, in many cases, in planta targets of pathogen-produced enzymes remain unknown. We identified a gene in the wheat pathogen Fusarium graminearum, encoding a putative enzyme that shows 84% sequence identity to FoToml, a tomatinase produced by the tomato pathogen Fusarium oxysporum f. sp. lycopersici. In F. oxysporum f. sp. lycopersici, FoToml is a virulence factor involved in the degradation of tomato defence compound tomatine, a saponin compound. Given that wheat is unknown to produce tomatine, we tested the ability of F. graminearum to degrade tomatine and found that F. graminearum was unable to degrade tomatine in culture. However, FgToml degraded tomatine in vitro when heterologously expressed. To determine the possible function of FgToml in pathogen virulence, we generated FgToml knockout mutants (Delta Tom1). Delta Tom1 mutants were not different from wild type when grown in culture but showed significant reduction in pathogen virulence in root rot and head blight assays. In an attempt to identify possible in planta targets of FgToml, the metabolomes of wheat heads infected with wildtype pathogen and AToml were compared and several peaks differentially abundant between treatments identified. Although the exact identity of these peaks is currently unknown, this result suggested that FgToml may have in planta targets in wheat, possibly tomatine-like saponin compounds. Overall, our results presented here show that FgToml is a new virulence factor in F. graminearum. (C) 2017 Elsevier Inc. All rights reserved.