Identification and Characterization of a Novel Hepta-Segmented dsRNA Virus From the Phytopathogenic Fungus Colletotrichum fructicola.

A novel hepta-segmented double-stranded RNA (dsRNA) virus was isolated and characterized from the strain FJ-4 of the phytopathogenic fungus Colletotrichum fructicola, and was named Colletotrichum fructicola chrysovirus 1 (CfCV1). The full-length cDNAs of dsRNA1-7 were 3620, 2801, 2687, 2437, 1750, 1536, and 1211 bp, respectively. The 5'- and 3'-untranslated regions of the seven dsRNAs share highly similar internal sequence and contain conserved sequence stretches, indicating that they have a common virus origin. The 5'-and 3'-UTRs of the seven dsRNAs were predicted to fold into stable stem-loop structures. CfCV1 contains spherical virions that are 35 nm in diameter consisting of seven segments. The largest dsRNA of CfCV1 encodes an RNA-dependent RNA polymerase (RdRp), and the second dsRNA encodes a viral capsid protein (CP). The dsRNA5 encodes a C2H2-type zinc finger protein containing an R-rich region and a G-rich region. The smallest dsRNA is a satellite-like RNA. The functions of the other proteins encoded by dsRNA3, dsRNA4, dsRNA6 are unknown. Phylogenetic analysis, based on RdRp and CP, indicated that CfCV1 is phylogenetically related to Botryosphaeria dothidea chrysovirus 1 (BdCV1), and Penicillium janczewskii chrysovirus 2 (PjCV2), a cluster of an independent cluster II group in the family Chrysoviridae. Importantly, all the seven segments of CfCV1 were transmitted successfully to other virus-free strains with an all-or-none fashion. CfCV1 exerts minor influence on the growth of C. fructicola but can confer hypovirulence to the fungal host. To our knowledge, this is the first report of a hepta-segmented tentative chrysovirus in C. fructicola.

A dsRNA mycovirus, Magnaporthe oryzae chrysovirus 1-B, suppresses vegetative growth and development of the rice blast fungus.

A double-stranded RNA (dsRNA) mycovirus was found in isolate S-0412-II 2a of the rice blast fungus Magnaporthe oryzae. Sequence analysis of the five dsRNA segments (dsRNA1 through dsRNA5) revealed that this mycovirus is closely related to Magnaporthe oryzae chrysovirus 1-A (MoCV1-A), tentatively classified as a member of the Chrysoviridae; therefore, it was named Magnaporthe oryzae chrysovirus 1-B (MoCV1-B). Virus particles were spherical and composed of the ORF1, ORF3 and ORF4 proteins. MoCV1-B-infected isolate S-0412-II 2a showed a more severe impaired phenotype than the MoCV1-A-infected isolate. In a virus-cured isolate, normal growth was restored, implied that MoCV1-B could be involved in this observed phenotype. An unanticipated result was the occurrence of a fungal isolate lacking dsRNA5. The nonessential dsRNA5 had higher sequence identity (96%) with dsRNA5 of MoCV1-A than with the other dsRNA segments (71-79%), indicating that dsRNA5 could be a portable genomic element between MoCV1-A and MoCV1-B.