Viral Effects of a dsRNA Mycovirus (PoV-ASI2792) on the Vegetative Growth of the Edible Mushroom Pleurotus ostreatus

Abstract

A double-stranded RNA (dsRNA) mycovirus was detected in malformed fruiting bodies of Pleurotus ostreatus strain ASI2792, one of bottle cultivated commercial strains of the edible oyster mushroom. The partial RNA-dependent RNA polymerase (RdRp) gene of the P. ostreatus ASI2792 mycovirus (PoV-ASI2792) was cloned, and a cDNA sequences alignment revealed that the sequence was identical to the RdRp gene of a known PoSV found in the P. ostreatus strain. To investigate the symptoms of PoV-ASI2792 infection by comparing the isogenic virus-free P. ostreatus strains with a virus-infected strain, isogenic virus-cured P. ostreatus strains were obtained by the mycelial fragmentation method for virus curing. The absence of virus was verified with gel electrophoresis after dsRNA-specific virus purification and Northern blot analysis using a partial RdRp cDNA of PoV-ASI2792. The growth rate and mycelial dry weight of virus-infected P. ostreatus strain with PoV-ASI2792 mycovirus were compared to those of three virus-free isogenic strains on 10 different media. The virus-cured strains showed distinctly higher mycelial growth rates and dry weights on all kinds of experimental culture media, with at least a 2.2-fold higher mycelial growth rate on mushroom complete media (MCM) and Hamada media, and a 2.7-fold higher mycelial dry weight on MCM and yeastmalt-glucose agar media than those of the virus-infected strain. These results suggest that the infection of PoV mycovirus has a deleterious effect on the vegetative growth of P. ostreatus.

The PoV mycovirus affects extracellular enzyme expression and fruiting body yield in the oyster mushroom, Pleurotus ostreatus

“…Virus-cured isogenic lines, which have identical genetic backgrounds, can then be established to explore direct mycovirus-fungal host interctions. As reported, we successfully obtained a PoV-cured strain as well as the PoV-infected strain from a malformed fruiting body, and verified the presence of the virus and its effect on the irregular colony growth of P. ostreatus 3 .…”

“…Morphological abnormality of the PoV-infected strain. In our initial survey of dysmorphic fruiting bodies of P. ostreatus ASI2792, we obtained abnormal mycelial cells, confirmed the presence of the PoV mycovirus (PoV-ASI2792) 3 , and examined the deleterious effects of mycoviral infection on the growth of fungal colonies using isogenic virus-cured and virus-infected fungal strains. In the present study, we attempted to better understand the relationship between PoV infection and the vegetative characteristics of P. ostreatus based on a pair-wise comparison of isogenic strains.…”

“…The fungal viruses are commonly latent, and hosts do not exhibit symptoms upon infection. Nevertheless, some mycoviruses cause severe morphological and physiological changes in fungal hosts, such as alterations of growth rate, colony morphology, spore production, pigmentation [1][2][3] , and enzymatic activities 4 . The first reported mycovirus (La France isometric virus, LIV) was found in 1962 in the cultivated mushroom Agaricus bisporus.…”

“…In the edible mushroom Pleurotus ostreatus, mycoviral infections can cause symptoms such as irregular mycelial growth rate, decreased fruiting body yield, and malformed fruiting bodies, and thus occasionally affect cultivation of the mushroom. As mentioned above, several mushroom diseases have been reported to be associated with mycoviruses, such as oyster mushroom spherical virus (OMSV) 6 , oyster mushroom isomeric virus (OMIV) 7 , P. ostreatus spherical virus (POSV) 8 , oyster mushroom dsRNA virus (OMDV) 9 , P. ostreatus virus 1 (PoV1) 10 , and P. ostreatus ASI2792 virus (PoV-ASI2792; PoV) 3 .…”

“…Mycoviruses infecting various hosts including P. ostreatus have been isolated and characterized. However, studies of mycovirus-host interactions have been insufficient to reveal the mechanisms involved in infection of P. ostreatus because it is difficult to secure definite isogenic virus-free or -cured strains to compare to virus-infected strains 3 . Because different genotypes of the same fungal species can produce inconsistent data with regard to identical mycovirus strains, various approaches have been used to obtain isogenic virus-cured strains, such as cycloheximide or ribavirin treatment, hyphal tip cutting, single-sporing, protoplast regeneration, or thermal stress treatment [11][12][13][14] .…”