Laminin-binding sites on cell walls of the entomopathogen Nomuraea rileyi associated with growth and adherence to host tissues

Abstract

The entomogenous hyphomycete Nomuraea rileyi replicates by budding or septation of yeast-like hyphal bodies in the hemocoels of host Spodoptera exigua (beet armyworm) larvae. Hyphal bodies are not recognized by host hemocytes and circulate freely in the hemolymph. Approximately 88 hours postinjection with 5 × 10³ hyphal bodies per larva, the hyphal bodies begin to form germ tubes which have the ability to attach to hemocytes and other host tissues, e.g., fat body. Immunofluorescence studies showed that laminin, a common component of the extracellular matrix in vertebrates and invertebrates, binds to germ tubes but not to hyphal bodies. Binding to germ tubes is saturable, and the major binding site, as indicated by Western blots of cell wall extracts, is apparently a mannoprotein with a molecular mass of 76 kilodaltons. Immunoelectron microscopy revealed that laminin binds to the fibrillar sheath covering the germ tube wall. Laminin also binds to conidia but not to conidial germ tubes. The significance of the differential binding of laminin to N. rileyi surfaces during morphogenesis of the fungus as related to recognition by host hemocytes and attachment to host tissues is discussed.

Key Words:

• entomogenous hyphomycete
• immunocytochemistry
• laminin
• Nomuraea rileyi