Family - Partitiviridae

Abstract

This chapter focuses on Partitiviridae family whose member genuses are Partitivirus, Alphacryptovirus, Betacryptovirus, and Cryspovirus. The virions of this family are isometric, nonenveloped, 30–43 nm in diameter and each virion contains 120 copies of a single capsid protein (CP) arranged as 60 dimers with T = 1 icosahedral symmetry. Dimeric surface protrusions are frequently observed on viral capsids. The virions contain two unrelated, linear dsRNA segments and the two segments of the individual viruses are usually of similar size. The genome consists of two linear dsRNA segments where the smaller one usually codes for the CP and the larger one usually codes for the virion-associated RNA polymerase. Each dsRNA is monocistronic and In vitro transcription/replication occurs by a semiconservative mechanism. The virions accumulate in the cytoplasm and are efficient immunogens. However, no serological relationships between the fungal viruses and the plant viruses in the family have been detected. The viruses are associated with latent infections of their fungal, protozoan and plant hosts and there are no known natural vectors. The fungal partitiviruses are transmitted intracellularly during cell division, hyphal anastomosis, and sporogenesis and in some ascomycetes, virus is usually eliminated during ascospore formation. Experimental transmission of purified fungal partitiviruses has been reported by transfection of virions into fungal protoplasts, and the plant cryptoviruses are transmitted by ovule and by pollen to the seed embryo.