Molecular characterization of a single-negative-stranded RNA virus from the rice blast fungus Magnaporthe oryzae isolate NJ39.

A novel negative-sense single-stranded RNA mycovirus, designated as "Magnaporthe oryzae mymonavirus 1" (MoMNV1), was identified in the rice blast fungus Magnaporthe oryzae isolate NJ39. MoMNV1 has a single genomic RNA segment consisting of 10,515 nucleotides, which contains six open reading frames. The largest open reading frame contains 5837 bases and encodes an RNA replicase. The six open reading frames have no overlap and are arranged linearly on the genome, but the spacing of the genes is small, with a maximum of 315 bases and a minimum of 80 bases. Genome comparison and phylogenetic analysis indicated that MoMNV1 is a new member of the genus Penicillimonavirus of the family Mymonaviridae.

A novel alternavirus with three dsRNA segments from Fusarium pseudograminearum, the pathogen of Fusarium crown rot in wheat.

Three dsRNA segments were detected in Fusarium pseudograminearum strain CF14029, a pathogen causing Fusarium crown rot in China. Characterization and sequence analysis confirmed that these dsRNA sequences originated from the same virus. The viral genome consists of three dsRNA segments: dsRNA1 (3,560 nt in length), encoding an RNA-dependent RNA polymerase (RdRp), dsRNA2 (2,544 nt in length), encoding a hypothetical protein, and dsRNA3 (2,478 nt in length), encoding a putative coat protein (CP). Phylogenetic analysis based on the RdRp and CP amino acid sequences revealed a high degree of similarity of this virus to members of the genus Alternavirus, family Alternaviridae, isolated from other Fusarium fungi. As a novel member of the genus Alternavirus, this virus was provisionally named "Fusarium pseudograminearum alternavirus 1" (FpgAV1). Like other alternaviruses found in Fusarium species, the positive-sense strand of each genomic dsRNA of FpgAV1 possesses a poly(A) tail and a distinctive 5'-terminal octamer sequence (5'-GCT GTG TG-3'). This is the first report of the genomic sequence of an alternavirus identified in F. pseudograminearum.

Four closely related endornaviruses each with a low incidence in the phytopathogenic fungi Exserohilum turcicum or Bipolaris maydis.

Endornaviruses are known to occur widely in plants, fungi, and oomycetes, but our understanding of their diversity and distribution is limited. In this study, we report the discovery of four endornaviruses tentatively named Setosphaeria turcica endornavirus 1 (StEV1), Setosphaeria turcica endornavirus 2 (StEV2), Bipolaris maydis endornavirus 1 (BmEV1), and Bipolaris maydis endornavirus 2 (BmEV2). StEV1 and StEV2 infect Exserohilum turcicum, while BmEV1 and BmEV2 infect Bipolaris maydis. The four viruses encode a polyprotein with less than 40 % amino acid sequence identity to other known endornaviruses, indicating that they are novel, previously undescribed endornaviruses. However, StEV1 and BmEV1 share a sequence identity of 78 % at the full-genome level and 87 % at the polyprotein level, suggesting that they may belong to the same species. Our study also found that each of the four endornaviruses has an incidence of approximately 3.5 % to 5.5 % in E. turcicum or B. maydis. Interestingly, BmEV1 and BmEV2 were found to be unable to transmit between hosts of different vegetative incompatibility groups, which may explain their low incidence.

Four distinct isolates of a novel polymycovirus identified in Setosphaeria turcica.

Isolation and analysis of double-stranded RNA (dsRNA) from the phytopathogenic fungus Setosphaeria turcica f. sp. zeae revealed the presence of a new double-stranded RNA (dsRNA) virus, tentatively named "Setosphaeria turcica polymycovirus 2" (StPmV2). The genome of StPmV2 consists of five segments (dsRNA1-5), ranging in size from 965 bp to 2462 bp. Each dsRNA contains one open reading frame (ORF) flanked by 5' and 3' untranslated regions (UTRs) with conserved terminal sequences. The putative protein encoded by dsRNA1 shows 64.52% amino acid sequence identity to the RNA-dependent RNA polymerase (RdRp) of the most closely related virus, Cladosporium cladosporioides virus 1, which belongs to the family Polymycoviridae. dsRNAs 2-4 encode the putative coat protein, methyltransferase (MTR), and proline-alanine-serine-rich protein (PASrp), respectively, and dsRNA5 encodes a protein of unknown function. Phylogenetic analysis based on the RdRp protein indicated that StPmV2 clustered with members of the family Polymycoviridae and is therefore a new mycovirus belonging to the genus Polymycovirus in the family Polymycoviridae. In addition, three other distinct isolates of StPmV2 were identified: one isolated from S. turcica f. sp. zeae and two from S. turcica f. sp. sorghi. To our knowledge, this is the first report of a polymycovirus infecting both S. turcica f. sp. zeae and S. turcica f. sp. sorghi.

Molecular and biological characteristics of a novel chrysovirus infecting the fungus phytopathogenic Setosphaeria turcica f.sp. sorghi.

A new double-stranded RNA (dsRNA) virus has been identified in the filamentous fungus Setosphaeria turcica f.sp. sorghi, whose genome consists of four segments (dsRNA1-4). Each dsRNA carries single open reading frame (ORF) flanked by 5' and 3' untranslated regions (UTRs) containing strictly conserved termini. The putative protein encoded by dsRNA1 showed 80.50% identity to the RNA-dependent RNA polymerase (RdRp) of the most closely related virus, Alternaria alternata chrysovirus 1 (AaCV1), belonging to the Chrysoviridae. dsRNA2 encodes the putative coat protein, while dsRNA3 and dsRNA4 respectively encode the hypothetical proteins of unknown functions. Phylogenetic analysis based on the RdRp protein indicated the virus clustered with members of the genus Betachrysovirus in the family Chrysoviridae. Based on the dsRNA profile, amino acid sequence comparisons, and phylogenetic analyses, the mycovirus is thought to be a new member of the family Chrysoviridae and designated as Setosphaeria turcica chrysovirus 1 (StCV1). Moreover, obvious differences were observed in the colony, mycelial and spore morphology between StCV1-infected and virus-cured strains of S. turcica f.sp. sorghi. StCV1 infection strongly reduced colony growth rate, spore production ability and virulence on host fungus. To our knowledge, this is the first report about mycovirus infecting S. turcica f.sp. sorghi and also the first chrysovirus infecting S. turcica.

Molecular characterization of a novel botourmiavirus with inverted complementary termini from the rice blast fungus Magnaporthe oryzae isolate HF04.

A novel positive-sense single-stranded RNA mycovirus, designated as "Magnaporthe oryzae botourmiavirus 10" (MoBV10), was identified in the rice blast fungus Magnaporthe oryzae isolate HF04. MoBV10 has a single genomic RNA segment consisting of 2,448 nucleotides, which contains a single open reading frame encoding an RNA-dependent RNA polymerase. Genome comparison and phylogenetic analysis indicated that MoBV10 is a new member of the genus Betascleroulivirus in the family Botourmiaviridae. The 5'- and 3'-terminal sequences of the genomic RNA of MoBV10 have inverted complementarity and potentially form a panhandle structure, which is very rare in RNA viruses.

Complete nucleotide sequence of a novel botourmiavirus from the rice blast fungus Magnaporthe oryzae isolate SH05.

A novel mycovirus with the proposed name "Magnaporthe oryzae botourmiavirus 9" (MoBV9) was found in the rice blast fungus Magnaporthe oryzae isolate SH05. The virus has a positive single-stranded RNA genome of 2,812 nucleotides and contains a single open reading frame predicted to encode an RNA-dependent RNA polymerase that is closely related to those of some unclassified viruses of the family Botourmiaviridae, including Plasmopara viticola lesion associated ourmia-like virus 44, Plasmopara viticola lesion associated ourmia-like virus 47, and Cladosporium uredinicola ourmiavirus 1. Genome sequence comparisons and phylogenetic analysis supported the notion that MoBV9 is a new member of the family Botourmiaviridae.

A novel previously undescribed fusarivirus from the phytopathogenic fungus Setosphaeria turcica.

A putative mycovirus belonging to the proposed family "Fusariviridae" was discovered in Setosphaeria turcica by sequencing a double-stranded RNA extracted from this phytopathogenic fungus. The virus was tentatively named "Setosphaeria turcica fusarivirus 1" (StFV1). StFV1 has a genome comprising 6685 nucleotides. The genome contains three open reading frames (ORF). The largest ORF, ORF1, is preceded by an untranslated region (UTR) of 16 nucleotides and separated from ORF2 by an intergenic region of 63 nucleotides. The smallest ORF, ORF3, overlaps ORF2 by 16 nucleotides and is followed by a 3'-UTR of 82 nucleotides. The protein encoded by ORF1 is 71.8%, 67.4% and 68.1% identical to the RNA-dependent RNA polymerases (RdRps) of Pleospora typhicola fusarivirus 1 (PtFV1), Plasmopara viticola lesion-associated fusarivirus 1 (PvlaFV1), and Plasmopara viticola lesion-associated fusarivirus 3 (PvlaFV3), respectively, but has less than 47% amino acid sequence identity to the RdRps of other fusariviruses. To our knowledge, this is the first fusarivirus discovered in S. turcica and the first virus to be identified in this fungus using conventional cloning methods.

A novel narnavirus from the plant-pathogenic fungus Magnaporthe oryzae.

A novel mycovirus with the proposed name "Magnaporthe oryzae narnavirus virus 1" (MoNV1), was described in the rice blast fungus Magnaporthe oryzae. The virus has a single-stranded (+ss) RNA genome of 2452 nucleotides, contains a single open reading frame (ORF) predicted to encode an RNA-dependent RNA polymerase (RDRP), and is closely related to some viruses of the genus Narnavirus, family Narnaviridae, including Aspergillus fumigatus narnavirus 1 (AfNV1), Neofusicoccum parvum narnavirus 2 (NpNV2) and Alternaria tenuissima narnavirus 1 (AtNV2). Genome sequence comparisons and phylogenetic analysis suggested that MoNV1 is a new member of the genus Narnavirus. The RDRPs of MoNV1 and some closely related narnaviruses do not contain a typical metal-binding "GDD" motif and catalytic site. Further studies are needed to investigate the replication mechanism of these viruses.

The complete genomic sequence of a novel alphapartitivirus from Bipolaris maydis, the causal agent of corn southern leaf blight.

A novel double-stranded RNA (dsRNA) mycovirus, designated Bipolaris maydis partitivirus 1 (BmPV1), was isolated from the plant pathogenic fungus Bipolaris maydis. The BmPV1 genome has two dsRNA segments. The larger segment (1,930 bp) has a single open reading frame (ORF) with a conserved RNA-dependent RNA polymerase domain. The smaller segment (1,790 bp) contains a single ORF encoding a putative coat protein. Homology searches and phylogenetic analysis indicated that BmPV1 is representative of a new species within the genus Alphapartitivirus.

Full-length sequence and genome analysis of CHV1-CN280, a North China isolate of cryphonectria hypovirus 1.

CHV1-CN280 is a North China isolate of cryphonectria hypovirus 1 (CHV1), which has high horizontal transmission ability. The complete genomic sequence of CHV1-CN280 was determined and analyzed. Compared with other reported CHV1s, the genome of CHV1-CN280 shows some significantly different characteristics. The junction of the two open reading frames (ORFs) of CHV1-CN280 is AUGUAUAA, while in other reported CHV1s, it is UAAUG. The genomic sequence of CHV1-CN280 shows a high level of similarity to other reported CHV1s in the 3' portion, but in some sections of the 5' portion (the region around the start codon of ORFA, the region around the predicted cleavage site of p29 and p40, and the 5'-portion of p48 coding region), the nucleotide sequence identity is lower than 50%. The p29 of CHV1-CN280 shares only about 60% identity with other sequenced CHV1 isolates at the amino acid level. Full-length genomic recombination analysis suggests that several recombination events have occurred in the ORFB coding region between CHV1-CN280 and two subtype I CHV1 isolates (CHV1-Euro7 or CHV1-EP721). RT-PCR primers were designed according to the genomic sequence of CHV1-CN280 to study the genetic diversity of CHV1 in East Asia. Phylogenetic analysis showed that the East Asian CHV1s were quite different from the five assigned subtypes in Europe, and seven new CHV1 subtypes were identified in this study.

Complete nucleotide sequence of Magnaporthe oryzae partitivirus 1.

A novel double-stranded RNA (dsRNA) mycovirus, designated Magnaporthe oryzae partitivirus 1 (MoPV1), was isolated from a strain of the plant pathogenic fungus Magnaporthe oryzae. The MoPV1 genome has two dsRNA genome segments. The larger segment (1763 bp) has a single open reading frame (ORF) with a conserved RNA-dependent RNA polymerase (RdRp) domain. The smaller segment (1491 bp) contains a single ORF encoding a putative coat protein (CP). Homology searches and phylogenetic analysis indicated that MoPV1 is a new member of the genus Gammapartitivirus. This is the first report of a mycovirus of the family Partitiviridae identified in Magnaporthe oryzae.