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.

GhMYC1374 regulates the cotton defense response to cotton aphids by mediating the production of flavonoids and free gossypol.

Myelocytomatosis (MYC) transcription factors (TFs) in plants are well-known regulators of plant defense against herbivores. However, the role and mechanism of MYC TFs in cotton (Gossypium hirsutum L.) defense against cotton aphids (Aphis gossypii Glover) remain still elusive. Herein, on the basis of aphid-induced cotton transcriptome analysis, GhMYC1374, a cotton MYC2-like TF that was highly induced by cotton aphid attack, has been identified that confers cotton aphid resistance in cotton. GhMYC1374 was an intranuclear transcription factor with three domains: bHLH-MYC_N, RBR and bHLH_AtAIB_like. GhMYC1374 was induced under cotton aphid feeding, exogenous methyl jasmonate (MeJA) and salicylic acid (SA) treatments. GhMYC1374 transient overexpression in cotton plants enhanced cotton aphid-resistance, while GhMYC1374 silence through VIGS (virus induced gene silencing) decreased cotton aphid-resistance. GhMYC1374 transient overexpression of in cotton plants activated the phenylpropane pathway and promoted the synthesis of flavonoids, and resistance to thus enhanced the cotton resistance against aphids. In contrast, GhMYC1374 silence inhibited the biosynthesis of flavonoids. In addition, GhMYC1374 also positively activated the expression of the biosynthetic genes of free gossypol, leading to the high content of free gossypol. Taken together, our results suggest that GhMYC1374 is involved in the cotton defense response against cotton aphids by regulating the biosynthesis of flavonoids and free gossypol.

GhMYB18 confers Aphis gossypii Glover resistance through regulating the synthesis of salicylic acid and flavonoids in cotton plants.

KEY MESSAGE: R2R3 MYB transcription factor GhMYB18 is involved in the defense response to cotton aphid by participating in the synthesis of salicylic acid and flavonoids. R2R3 MYB transcription factors (TFs) play crucial roles in plant growth and development as well as response to abiotic and biotic stresses. However, the mechanism of R2R3 MYB TFs in cotton response to aphid infestation remains largely unknown. Here, an R2R3 MYB transcription factor GhMYB18 was identified as a gene up-regulated from upland cotton (Gossypium hirsutum L.) under cotton aphid (Aphis gossypii Glover) infestation. GhMYB18, which has transcription activity, was localized mainly to nucleus and cell membranes. Transient overexpression of GhMYB18 in cotton activates salicylic acid (SA) and phenylpropane signaling pathways and promoted the synthesis of salicylic acid and flavonoids, which leads to enhancing the tolerance to cotton aphid feeding. In contrast, silencing of GhMYB18 increased the susceptibility of G. hirsutum to aphid. Additionally, GhMYB18 significantly promoted the activities of defense-related enzymes including catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL). These results collectively suggest that GhMYB18 is involved in cotton defense response to cotton aphid attacks through regulating the synthesis of salicylic acid and flavonoids.

Molecular characterization of a putative alphapartitivirus from Impatiens balsamina L.

Two double stranded RNAs (dsRNAs) that likely represent the genome of an alphapartitivirus, tentatively named "impatiens cryptic virus 1" (ICV1), were recovered from Impatiens balsamina L. RNA1 (2008 bp) codes for the RNA-dependent RNA polymerase (RdRp) of ICV1, which shares <83% amino acid sequence identity with the RdRps of other alphapartitiviruses. RNA2 (1906 bp) codes for the coat protein (CP) of ICV1, which shares <60% amino acid sequence identity with the CPs of other alphapartitiviruses. Phylogenetic analysis suggested that ICV1 is closely related to plant alphapartitiviruses, including vicia cryptic virus, beet cryptic virus 1, carrot cryptic virus, and white clover cryptic virus 1. Using primers specific for RNA1 or RNA2, ICV1 could be detected in I. balsamina from various parts of China.

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.

Molecular characterization of a novel polymycovirus from the phytopathogenic fungus Setosphaeria turcica.

A putative polymycovirus tentatively named "Setosphaeria turcica polymycovirus 1" (StPmV1) was discovered in the phytopathogenic fungus Setosphaeria turcica. StPmV1 has a genome comprising five double-stranded RNAs (dsRNAs). dsRNA1, 2, and 3 each encode a protein sharing significant similarity but lower than 64% sequence identity to the corresponding proteins of other polymycoviruses. dsRNA4 and 5 each encode a protein with a sequence that is not conserved among polymycoviruses. However, the protein encoded by dsRNA4 is rich in proline (P), alanine (A), and serine (S) residues, which is a feature shared by the so-called PAS-rich proteins encoded by all polymycoviruses. Phylogeny reconstruction using the RNA-dependent RNA polymerase (RdRp) sequences of accepted or putative polymycoviruses revealed that StPmV1 is most closely related to Plasmopara viticola lesion associated polymycovirus 1 (PvaPolymyco1), a putative polymycovirus recovered from the phytopathogenic oomycetes Plasmopara viticola. These data suggest that StPmV1 may represent a novel species of the genus Polymycovirus, family Polymycoviridae. To our knowledge, this is the first polymycovirus reported from S. turcica.

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.

Four distinct isolates of Helminthosporium victoriae virus 190S identified from Bipolaris maydis.

Helminthosporium victoriae virus 190S (HvV190S) is the type species of the genus Victorivirus under the family Totiviridae. To date, HvV190S has never been found in places outside of the USA and has Helminthosporium victoriae as its only know natural host fungus in the field. Here, we report the identification of 4 double-stranded RNA (dsRNA) viruses from Bipolaris maydis in Hubei province of China. Interestingly, the genomes of the 4 viruses show 81.2 %-85.5 % nucleotide sequence identities to HvV190S. Their capsid protein (CP) and RNA-dependent RNA polymerase (RdRp) share 95.5-97.9 % and 94.6-96.6 % amino acid sequence identities to corresponding proteins of HvV190S. Therefore, the 4 viruses, which show 81.8-87.3 % pairwise genome sequence identities, should be considered as distinct isolates of HvV190S. Our finding suggests that HvV190S is widely distributed in the world and may infect fungal species other than H. victoriae.

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.

Identification and formation mechanism of a novel noncoding RNA produced by avian infectious bronchitis virus.

Viral noncoding (nc) RNAs have been shown to play important roles in viral life cycle. Many viruses employ different mechanism to produce ncRNAs. Here, we report that coronavirus infectious bronchitis virus (IBV) produces a novel ncRNA in virus-infected cells. This ncRNA consists of 563 nucleotides excluding a poly(A) tail, is mainly derived from the 3'-untranslated region of IBV genome, and contains a 63-nt-long of terminal leader sequence derived from the 5' end of the viral genome. Using mutagenesis and reverse genetics, we reveal that this ncRNA is a subgenomic RNA generated by discontinuous transcription mechanism.

Complete genome sequence of a new strain of Lagenaria siceraria endornavirus from China.

An RNA virus tentatively named Lagenaria siceraria endornavirus-Hubei (LsEV-HuB) was isolated from Lagenaria siceraria var. hispida in Hubei, China. The LsEV-HuB genome consists of 15,098 bp and contains a single open reading frame (ORF) encoding a large protein with several conserved domains, including one helicase domain, one glycosyltransferase domain, two capsular polysaccharide synthesis protein (CPS) domains, and one RNA-dependent RNA polymerase (RdRp) domain. LsEV-HuB has nucleotide and amino acid sequence identities of 72.96% and 77.95%, respectively, to Lagenaria siceraria endornavirus-California (LsEV-CA), the closest relative of LsEV-HuB.

A new putative deltapartitivirus recovered from Dianthus amurensis.

Two double stranded RNAs (dsRNA), likely representing the genome of a novel deltapartitivirus, provisionally named carnation cryptic virus 3 (CCV3), were recovered from Dianthus amurensis. The two dsRNAs were 1,573 (dsRNA1) and 1,561 (dsRNA2) bp in size, each containing a single open reading frame (ORF) encoding a 475- and 411-aa protein, respectively. The 475-aa protein contains a conserved RNA dependent RNA polymerase (RdRp) domain which shows significant homology to RdRps of established or putative partitiviruses, particularly those belonging to the genus Deltapartitivirus. However, it shares an amino acid identity of 75% with its closest relative, the RdRp of the deltapartitivirus beet cryptic virus 2 (BCV2), and is <62% identical to the RdRps of other partitiviruses. In a phylogenetic tree constructed with RdRps of selected partitiviruses, CCV3 clustered with BCV2 and formed a well-supported monophyletic clade with known or putative deltapartitiviruses.