Five Questions about Mycoviruses

Mycoviruses are viruses that infect fungi. The first mycovirus was reported in 1962 from the cultivated mushroom, Agaricus bisporus; the infected mushrooms developed malformed fruiting bodies, grew slowly, and matured early, resulting in serious yield losses [1]. Like viruses that infect animals and plants, mycoviruses require the living cells of other organisms to replicate. While sharing some characteristics with animal and plant viruses, mycoviruses also have the following unique characteristics: (1) most mycoviruses lack an extracellular route for infection; (2) mycoviruses are transmitted intercellularly only through cell division, sporulation, and cell fusion; and (3) mycoviruses apparently lack a movement protein, which is essential for the life cycle of animal and plant viruses. According to the most recent report concerning virus taxonomy, the genome of most mycoviruses consists of double-stranded RNA (dsRNA), while the genome of about 30% of mycoviruses is composed of a positive, single-stranded RNA (+ssRNA) [2]. A geminivirusrelated DNAmycovirus was recently reported for the first time [3]. Mycoviruses have been detected in all of the major phyla of fungi, including the Chytridiomycota, Zygomycota, Ascomycota, Deuteromycota, and Basidiomycota [1]. Although many mycoviruses and their host fungi have been identified, many mycoviruses undoubtedly remain unknown. Recently developed metagenomic approaches will be useful for detecting and identifying new mycoviruses.