Abstract
A novel double-stranded RNA (dsRNA) mycovirus, consisting of three dsRNA genome segments and possibly belonging to the family Chrysoviridae, was isolated from the filamentous phytopathogenic fungus Colletotrichum gloeosporioides and designated as Colletotrichum gloeosprioides chrysovirus 1 (CgCV1). The three dsRNAs of the CgCV1 genome with lengths of 3397, 2869, and 2630 bp (dsRNAs1–3) were found to contain a single open reading frame (ORF) putatively encoding the RNA-dependent RNA polymerase (RdRp), a capsid protein, and a protease, respectively, all of which exhibited some degree of sequence similarity to the comparable putative proteins encoded by the genus Chrysovirus. The 5′- and 3′-untranslated regions in each dsRNA segment contained similar sequences that were strictly conserved at the termini. Moreover, isometric virus-like particles (VLPs) with a diameter of approximately 40 nm were extracted from fungal mycelia. Phylogenetic analysis based on the conserved dsRNA1-encoded RdRp showed that CgCV1 is a new virus belonging to the Chrysoviridae family. BLAST analysis revealed the presence of CgCV1-like sequences in the chromosomes of Medicago truncatula and Solanum tuberosum. Moreover, some sequences in the transcriptome shotgun assembly (TSA) library and expressed sequence tag database (ESTdb) of other eudicot and monocot plants were also found to be related to CgCV1.
Highlights
Mycoviruses have been identified in almost all major groups of the kingdom Fungi, and an increasing number of novel mycoviruses have been reported [1,2,3]
We deduced that the three double-stranded RNA (dsRNA) segments constitute a novel chrysovirus named ‘Colletotrichum gloeosprioides chrysovirus 1 (CgCV1)’, regardless of their trisegmented genome
The three segments shared conserved terminal sequences at both ends, especially the terminal sequence stretch (GAUAAAA), which existed in all three dsRNA segments and was shared by other chrysoviruses
Summary
Mycoviruses have been identified in almost all major groups of the kingdom Fungi, and an increasing number of novel mycoviruses have been reported [1,2,3]. The presence of many mycoviruses is associated with latent infections (appearing asymptomatic) in their hosts. Some mycoviruses can incapacitate the virulence of their phytopathogenic fungal hosts, which may be exploited for biological control (e.g., the successful control of the chestnut blight in Europe) using the hypovirulent strains of its pathogen, caused by Cryphonectria hypovirus 1 (CHV1) [4]. The viruses in the family Chrysoviridae are commonly comprised of four monocistronic double-stranded RNA (dsRNA) segments ranging in size from 2.4 kbp to 3.6 kbp, separately encapsidated by non-enveloped isometric particles 35–40 nm in diameter. 145S virus (HvV145S), the type species), viruses in the family Chrysoviridae often encode an RNA-dependent RNA polymerase (RdRp), capsid protein (CP), putative protease, and a protein. Chrysoviruses, as well as other mycoviruses in the families of Totiviridae and Partitiviridae, infect fungi and plants [7]
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