Characterization of a mycovirus associated with the brown discoloration of edible mushroom, Flammulina velutipes

Yumi Magae,Masahide Sunagawa

doi:10.1186/1743-422x-7-342

Yumi Magae, Masahide Sunagawa

Open Access

https://doi.org/10.1186/1743-422x-7-342

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Abstract

BackgroundA mycovirus previously identified in brown discolored fruiting bodies of the cultivated mushroom Flammulina velutipes was characterized. We tentatively named the virus the F. velutipes browning virus (FvBV).ResultsPurified FvBV particles contained two dsRNA genomes (dsRNA1 and 2). The complete sequence of dsRNA1 was 1,915 bp long, containing a single open reading frame (ORF) that encoded 580 amino acids of a putative 66-kDa RNA-dependent RNA polymerase (RdRp). dsRNA2 was 1,730 bp long containing a single ORF encoding 541 amino acids of a putative 60-kDa coat protein (CP1). Phylogenetic analysis of the RdRp sequences revealed FvBV to be a Partitivirus, most closely related to Chondrostereum purpureum cryptic virus. An RT-PCR assay was developed for the amplification of a 495-bp cDNA fragment from dsRNA encoding the CP1. When wild F. velutipes isolated from various parts of Japan were examined by RT-PCR assay, three isolates from the central region of Japan contained FvBV. One wild strain infected with FvBV was isolated in Nagano prefecture, where brown discoloration of white cultivated strains has occurred. Fruiting bodies produced by virus-harboring and virus-free F. velutipes were compared.ConclusionsCap color of the fruiting bodies of F. velutipes that contained Partitivirus FvBV was darker than FvBV-free fruiting bodies. The use of RT-PCR enabled association of FvBV and dark brown color of the fruiting body produced by F. velutipes strains.

Highlights

A mycovirus previously identified in brown discolored fruiting bodies of the cultivated mushroom Flammulina velutipes was characterized
Molecular characterization of F. velutipes browning virus (FvBV) The complete nucleotide sequences of the two dsRNAs isolated from the purified virions (Figure 1) were determined
DsRNA1: The sequence of dsRNA1 was 1,915 bp in length, containing a single open reading frame (ORF) starting at position nt 56 and ending at nt 1798, which encoded a putative protein of 580 amino acids with a deduced molecular mass of 66,716 Da (Figure 2)

Summary

Introduction

A mycovirus previously identified in brown discolored fruiting bodies of the cultivated mushroom Flammulina velutipes was characterized. At the time mycoviruses were discovered in the white button mushroom, Agaricus bisporus, in 1962 [1], Lentinula edodes was the only artificially cultivated mushroom in Japan. The number of cultivated mushroom species has greatly increased: L. edodes, Flammulina velutipes, Hypsizygus marmoreus, Pholiota nameko, Grifola frondosa, and Pleurotus eryngii are cultivated daily. As the mushroom industry in Japan continues to grow, various abnormal symptoms during cultivation have been observed. Symptom that resembled abiotic disorders of A. bisporus [2] first became apparent with cultivated strains of F. velutipes [3,4]. One of the abnormal symptoms was the spontaneous appearance of brown discolored fruiting bodies among the white ones.

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