Structure-Based Comparative Analysis Reveals the Landscape of Powdery Mildew Secretomes Across Five Genera

Powdery mildew fungi are major obligate biotrophic plant pathogens, that cause widespread disease in agricultural and natural ecosystems worldwide, but a comparative structural view of their secretomes across multiple genera has remained limited. Here, we performed computational structure prediction and comparative analysis of 7545 secretome candidates from 26 isolates representing five genera (Blumeria, Erysiphe, Golovinomyces, Parauncinula, and Podosphaera) using AlphaFold2-based structure prediction, structural annotation against CATH, SCOPe, and PDB, Foldseek-based clustering and network analysis, structure-based grouping of RALPH (RNase-like proteins associated with haustoria) candidates, and comparison with defined fungal effector structural families. The predicted secretomes showed comparable model confidence across isolates and revealed a conserved structural core composed of recurrent microbial ribonuclease, immunoglobulin/fibronectin-like, glycosidase-related, and other enzyme-associated folds, with MoHrip2-like representing the most prominent shared fold among defined fungal effector structural families. Structural clustering and network analysis identified a prominent RALPH-centered component with additional conserved and lineage-enriched communities. RALPH candidates formed a structurally diverse repertoire that could be partitioned into 15 topology-defined groups, several linked to previously characterized powdery mildew effectors. Blumeria was structurally distinct, showing expansion of RALPH-associated components and the absence of multiple fold/domain categories retained in dicot-associated genera. Together, these results establish a comparative structural landscape of powdery mildew secretomes and provide a framework for future functional, evolutionary, and genomics-driven studies of conserved and lineage-associated secretome candidate.