Summary auto-generated
This study used gold-labeled antibodies to visualize the location of Pr1, a cuticle-degrading protease produced by the entomopathogenic fungus Metarhizium anisopliae during infection of tobacco hornworm (Manduca sexta) cuticles. Using electron microscopy, researchers tracked Pr1 secretion from fungal infection structures called appressoria and from penetrating hyphae as the fungus invaded the host cuticle. The enzyme was initially confined to fungal cell walls and immediate surroundings but gradually diffused throughout the cuticle during later infection stages. The results demonstrated that fungal penetration of the insect cuticle employs two mechanisms: enzymic degradation of the epicuticle (outer layer) and a combination of enzymic degradation plus mechanical separation of lamellar structures in the procuticle (inner layer). Melanized (pigmented) regions of cuticle proved more resistant to enzymic digestion than unpigmented areas. The findings confirm that Pr1 plays a crucial role in M. anisopliae's ability to infect insects and suggest similar mechanisms may apply to other fungal pathogens of insects.
Key findings
- Pr1 protease is secreted by M. anisopliae infection structures (appressoria) and penetrating hyphae, initially localizing to fungal cell walls before diffusing throughout the cuticle
- Epicuticle penetration occurs primarily through enzymic degradation, while procuticle penetration involves both enzymic digestion and mechanical separation of structural layers
- Gold particles densely labeled hyphal cell walls when the fungus was cultured under conditions promoting Pr1 production, confirming rapid enzyme secretion after synthesis
- Melanized regions of cuticle resisted enzymic digestion more effectively than unpigmented areas
- The localization and temporal distribution of Pr1 demonstrates its essential role in the fungal invasion process of insect hosts
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
SUMMARY: Gold-labelled rabbit antiserum was used to demonstrate that a cuticle-degrading protease (Pr1) is produced by Metarhizium anisopliae during penetration of host (Manduca sexta) procuticle. The protease was secreted by infection structures (appressoria) on the cuticle surface and by the penetrant hyphae within the cuticle. Penetration of the procuticle was by a combination of enzymic degradation and mechanical pressure. Initially Pr1 was confined to the immediate vicinity of the fungal structures; however the enzyme diffused throughout the cuticle during later stages of pathogenesis. When hyphae were labelled during growth in culture under conditions conducive to rapid synthesis of Pr1, gold particles distributed over the fungal cell wall, indicating binding of Pr1 to hyphae.