Bi Da Gao

A novel nonsegmented double-stranded RNA mycovirus identified in the phytopathogenic fungus Nigrospora oryzae shows similarity to partitivirus-like viruses

Nigrospora oryzae is a pathogen that can infect plants of various species. Here, we report the isolation of a novel mycovirus from N. oryzae infecting rice, as well as the complete genome sequence and genomic organization of this virus, which we have named “Nigrospora oryzae nonsegmented RNA virus 1” (NoNRV1). The genome of NoNRV1 contained two non-overlapping open reading frames (ORF1 and ORF2) potentially encoding a protein with an unknown function in ORF1 and a putative RNA-dependent RNA polymerase (RdRp) in ORF2. Homology and phylogenetic analysis revealed that NoNRV1 was most similar to the Ustilaginoidea virens nonsegmented virus 1 (UvNV-1) and distantly related to members of the virus family Partitiviridae. It is proposed that NoNRV1, together with UvNV-1 and other related viruses, might represent a novel virus taxon of mycoviruses belonging to a partitivirus-like lineage.

Molecular identification of a novel victorivirus from the phytopathogenic fungus Nigrospora oryzae

Nigrospora oryzae is a worldwide phytopathogenic fungus that can infect many plant host species. In this study, complete sequence of a novel mycovirus from N. oryzae was reported. The viral genome is 5100 base pairs in length and possesses two overlapping open reading frames (ORFs). The two ORFs potentially encode proteins that showed significant similarity to the capsid protein and RNA-dependent RNA polymerase, in the family Totiviridae, respectively. Phylogenetic tree showed that this novel mycovirus is a new member of the genus Victorivirus in the family Totiviridae. We here designated the virus as Nigrospora oryzae victorivirus 1 (NoRV1), the first putative victorivirus identified in N. oryzae.

A novel fusarivirus isolated from the phytopathogenic fungus Nigrospora oryzae

In this study, we report the discovery and molecular characterization of a novel mycovirus, Nigrospora oryzae fusarivirus 1 (NoFV1) isolated from the rice-infecting fungus Nigrospora oryzae. Excluding a poly (A) tail, the genome of the virus is 7004 nucleotide (nt) long containing three putative nonoverlapping open reading frames (ORF1, ORF2, and ORF3). The large ORF1 encodes a polypeptide with a conserved RNA-dependent RNA polymerase (RdRp) domain and a helicase domain that functions for RNA replication. Each of the smaller ORF2 and the smallest ORF3 encodes a putative protein with an unknown function. Amino acid (aa) sequence similarities between the NoFV1-ORF1- and ORF2-encoded proteins and the homologous sequences from other mycoviruses were found. Phylogenetic analysis on the basis of the RdRp and helicase domains showed that NoFV1 is phylogenetically related to viruses in the newly proposed family Fusariviridae. Thus, we suggest that NoFV1 might be a novel member of family Fusariviridae.

Molecular characterization of a putative gammapartitivirus in the phytopathogenic fungus Nigrospora oryzae

We report the molecular attributes of a novel bisegmented double-stranded RNA (dsRNA) virus, designated “Nigrospora oryzae partitivirus 1” (NoPV1), from a phytopathogenic fungus Nigrospora oryzae. The genome of NoPV1 contains two dsRNA segments (dsRNA1 and 2), 1875 bp and 1601 bp in length, respectively. dsRNA1 and -2 both have a single open reading frame encoding the RNA-dependent RNA polymerase and coat protein, respectively. NoPV1 has a high degree of sequence identity to members of genus Gammapartitivirus in the family Partitiviridae. This is the first report of a mycovirus in the family Partitiviridae that infects N. oryzae.

A mitovirus isolated from the phytopathogenic fungus Alternaria brassicicola

Alternaria brassicicola is one of the causal agents of alternaria blackspot in rapeseed. In this study, a dsRNA segment was isolated and sequenced from the fungus. The complete nucleotide sequence of the dsRNA was 2506 bp in length and, using the fungal mitochondrial genetic code, was predicted to contain a single large open reading frame (ORF) in the positive strand. This ORF was predicted to encode a protein with 719 amino acids that contains characteristic conserved motifs of the RNA-dependent RNA polymerase (RdRp). BLAST analysis revealed that this protein had significant sequence similarity to the RdRp from viruses of the genus Mitovirus. These results indicated that the dsRNA segment represents the replicative form of a mitovirus, which is tentatively designated “Alternaria brassicicola mitovirus 1” (AbMV1) and is a new member of the genus Mitovirus in the family Narnaviridae.