Discovery and characterization of a novel Lepidoptera‐specific antimicrobial peptide from the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract Antimicrobial peptides (AMPs) are critical components of innate immunity in diverse organisms, including plants, vertebrates, and insects. This study identified and characterized a novel Lepidoptera‐specific AMP, named lepidoptin, from the invasive pest Spodoptera frugiperda (Lepidoptera: Noctuidae). Lepidoptin is a 116‐amino acid protein containing a signal peptide and a novel β ‐sandwich domain that is distinct from previously reported AMPs. Temporal and spatial expression analyses revealed a significant upregulation of the lepidoptin gene in vivo and in cultured SF9 cells in response to pathogens. Molecular docking analysis identified a specific binding cavity. Enzyme‐linked immunosorbent assay and binding assays confirmed that lepidoptin can bind to pathogen‐associated molecular patterns, bacteria, and fungi. Recombinant lepidoptin exhibited potent antibacterial activity by inducing bacterial agglutination, inhibiting bacterial growth, increasing bacterial membrane permeability, and preventing biofilm formation. Lepidoptin also showed antifungal activity against the entomopathogenic fungus Beauveria bassiana by inhibiting spore germination, increasing fungal cell permeability, and increasing reactive oxygen species. Injection of recombinant lepidoptin into S. frugiperda larvae increased survival after B. bassiana infection, whereas knockdown of lepidoptin by RNA interference decreased larval survival. In addition, lepidoptin showed antimicrobial activity against the plant pathogen Fusarium graminearum by inhibiting spore germination and alleviating disease symptoms in wheat seedlings and cherry tomatoes. This study demonstrates the remarkable dual functionality of lepidoptin in enhancing S. frugiperda immunity and controlling plant pathogens, making it a promising candidate for biocontrol strategies in both pest management and plant disease prevention.