Insect I‐Type Lysozymes Function as Antiviral Proteases by Forming Biomolecular Condensates

Abstract Lysozymes are well‐known for their ability to cleave bacterial peptidoglycan, but their potential to hydrolyze viral components as a form of antiviral defense remains poorly understood. This study demonstrates that insect i‐type lysozymes (Lyz‐I1), regulated by the Toll signaling pathway, function as proteases that directly cleave viral proteins. Structural and functional analyses reveal that the catalytic dyad Glu34/Asp50 in leafhopper Lyz‐I1, while retaining its essential role in bacterial peptidoglycan hydrolysis, also mediates specific binding to Lys180 on the viroplasm protein Pns9 of rice gall dwarf virus (RGDV). This interaction catalyzes the cleavage of the adjacent peptide bond of Lys180, leading to Pns9 degradation, which disrupts viroplasm assembly and inhibits viral replication. Notably, this proteolytic antiviral mechanism of Lyz‐I1 shows evolutionary conservation across major rice reoviruses and their respective leafhopper or planthopper vectors. Additionally, leafhopper Lyz‐I1 undergoes liquid–liquid phase separation, forming biomolecular condensates that concentrate Pns9 and enhance proteolytic efficiency. Critically, exogenous application of Lyz‐I1 not only effectively reduces viral titer and disease symptoms in RGDV‐infected rice plants but also induces plant immune defense. Consequently, this work provides the evidence that lysozymes can function as specific antiviral proteases, establishing a foundation for innovative control strategies against viral diseases.