Ultrastructural features of fungal virus-like particles from Lentinus edodes

Abstract

Polyhedral virus-like particles approximately 39 nm in diameter (39-nm VLPs) from Lentinus edodes (Berk.) Sing. have been studied in vitro and in vivo by electron microscopy. Examination of negatively stained and rotary shadowed preparations of partially purified 39-nm VLPs showed that: (1) the particles have a double-shelled structure consisting of an outer capsid shell and an inner core containing a double-stranded RNA (dsRNA) ( Ushiyama et al., Virology 77, 880–883, 1977 ), suggesting that this basic structure is closely similar to that of viruses belonging to the Reoviridae; and (2) some filamentous structures were bound to the exterior of capsids, and they were frequently found to be a feature of partial-core particles. Observations on ribonuclease-treated and rotary-shadowed preparations of 39-nm VLPs in vitro suggested that the extra-viral filaments attached to capsids might be dsRNA. Further observations on 39-nm VLPs which were isolated from glutaraldehyde-fixed mycelia, and on those in thin sections of hyphal cells, suggested that at least some particles might discharge dsRNA from their cores in vivo.