Characterization of Two Novel Single-Stranded RNA Viruses from Agroathelia rolfsii, the Causal Agent of Peanut Stem Rot.

Peanut stem rot is a soil-borne disease caused by Agroathelia rolfsii. It occurs widely and seriously affects the peanut yield in most peanut-producing areas. The mycoviruses that induce the hypovirulence of some plant pathogenic fungi are potential resources for the biological control of fungal diseases in plants. Thus far, few mycoviruses have been found in A. rolfsii. In this study, two mitoviruses, namely, Agroathelia rolfsii mitovirus 1 (ArMV1) and Agroathelia rolfsii mitovirus 2 (ArMV2), were identified from the weakly virulent A. rolfsii strain GP3-1, and they were also found in other A. rolfsii isolates. High amounts of ArMV1 and ArMV2in the mycelium could reduce the virulence of A. rolfsii strains. This is the first report on the existence of mitoviruses in A. rolfsii. The results of this study may provide insights into the classification and evolution of mitoviruses in A. rolfsii and enable the exploration of the use of mycoviruses as biocontrol agents for the control of peanut stem rot.

A Novel Strain of Fusarium oxysporum Alternavirus 1 Isolated from Fusarium oxysporum f. sp. melonis Strain T-BJ17 Confers Hypovirulence and Increases the Sensitivity of Its Host Fungus to Difenoconazole and Pydiflumetofen.

In the current study, a novel strain of Fusarium oxysporum alternavirus 1 (FoAV1) was identified from the Fusarium oxysporum f. sp. melonis (FOM) strain T-BJ17 and was designated as Fusarium oxysporum alternavirus 1-FOM (FoAV1-FOM). Its genome consists of four dsRNA segments of 3515 bp (dsRNA1), 2663 bp (dsRNA2), 2368 bp (dsRNA3), and 1776 bp (dsRNA4) in length. Open reading frame 1 (ORF1) in dsRNA1 was found to encode a putative RNA-dependent RNA polymerase (RdRp), whose amino acid sequence was 99.02% identical to that of its counterpart in FoAV1; while ORF2 in dsRNA2, ORF3 in dsRNA3, and ORF4 in dsRNA4 were all found to encode hypothetical proteins. Strain T-BJ17-VF, which was verified to FoAV1-FOM-free, was obtained using single-hyphal-tip culture combined with high-temperature treatment to eliminate FoAV1-FOM from strain T-BJ17. The colony growth rate, ability to produce spores, and virulence of strain T-BJ17 were significantly lower than those of T-BJ17-VF, while the dry weight of the mycelial biomass and the sensitivity to difenoconazole and pydiflumetofen of strain T-BJ17 were greater than those of T-BJ17-VF. FoAV1-FOM was capable of 100% vertical transmission via spores. To our knowledge, this is the first time that an alternavirus has infected FOM, and this is the first report of hypovirulence and increased sensitivity to difenoconazole and pydiflumetofen induced by FoAV1-FOM infection in FOM.

Complete Genome Analyses of a Novel Flexivirus with Unique Genome Organization and Three Endornaviruses Hosted by the Mycorrhizal Fungus Terfezia claveryi.

The extensive use of high-throughput sequencing (HTS) has significantly advanced and transformed our comprehension of virus diversity, especially in intricate settings like soil and biological specimens. In this study, we delved into mycovirus sequence surveys within mycorrhizal fungus species Terfezia claveryi, through employing HTS with total double-stranded RNA (dsRNA) extracts. Our findings revealed the presence of four distinct members from the Alsuviricetes class, one flexivirus designated as Terfezia claveryi flexivirus 1 (TcFV1) and three endornaviruses (TcEV1, TcEV2, and TcEV3) in two different T. claveryi isolates. TcFV1, a member of the order Tymovirales, exhibits a unique genome structure and sequence features. Through in-depth analyses, we found that it shares sequence similarities with other deltaflexiviruses and challenges existing Deltaflexiviridae classification. The discovery of TcFV1 adds to the genomic plasticity of mycoviruses within the Tymovirales order, shedding light on their evolutionary adaptations. Additionally, the three newly discovered endornaviruses (TcEV1, TcEV2, and TcEV3) in T. claveryi exhibited limited sequence similarities with other endornaviruses and distinctive features, including conserved domains like DEAD-like helicase, ATPases Associated with Diverse Cellular Activities (AAA ATPase), and RNA dependent RNA polymerase (RdRp), indicating their classification as members of new species within the Alphaendornavirus genus. In conclusion, this research emphasizes the importance of exploring viral diversity in uncultivated fungi, bridging knowledge gaps in mycovirus ecology. The discoveries of a novel flexivirus with unique genome organization and endornaviruses in T. claveryi broaden our comprehension of mycovirus diversity and evolution, highlighting the need for continued investigations into viral populations in wild fungi.

Molecular characterization of a new botybirnavirus that infects Alternaria sp. from tobacco.

The genus Alternaria comprises many important fungal pathogens that infect a wide variety of organisms. In this report, we present the discovery of a new double-stranded RNA (dsRNA) mycovirus called Alternaria botybirnavirus 2 (ABRV2) from a phytopathogenic strain, XC21-21C, of Alternaria sp. isolated from diseased tobacco leaves in China. The ABRV2 genome consists of two dsRNA components, namely dsRNA1 and dsRNA2, with lengths of 6,162 and 5,865 base pairs (bp), respectively. Each of these genomic dsRNAs is monocistronic, encoding hypothetical proteins of 201.6 kDa (P1) and 2193.3 kDa (P2). ABRV2 P1 and P2 share 50.54% and 63.13% amino acid sequence identity with the corresponding proteins encoded by dsRNA1 of Alternaria botybirnavirus 1 (ABRV1). Analysis of its genome organization and phylogenetic analysis revealed that ABRV2 is a new member of the genus Botybirnavirus.

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.

Complete genome sequence of a novel mitovirus identified in the phytopathogenic fungus Fusarium oxysporum f. sp. melonis strain T-SD3.

A novel mitovirus was identified in Fusarium oxysporum f. sp. melonis strain T-SD3 and designated as "Fusarium oxysporum mitovirus 3" (FoMV3). The virus was isolated from diseased muskmelon plants with the typical symptom of fusarium wilt. The complete genome of FoMV3 is 2269 nt in length with a predicted AU content of 61.40% and contains a single open reading frame (ORF) using the fungal mitochondrial genetic code. The ORF was predicted to encode a polypeptide of 679 amino acids (aa) containing a conserved RNA-dependent RNA polymerase (RdRp) domain with a molecular mass of 77.39 kDa, which contains six conserved motifs with the highly conserved GDD tripeptide in motif IV. The 5'-untranslated region (UTR) and 3'-UTR of FoMV3 were predicted to fold into stem-loop structures. BLASTp analysis revealed that the RdRp of FoMV3 shared the highest aa sequence identity (83.85%) with that of Fusarium asiaticum mitovirus 5 (FaMV5, a member of the family Mitoviridae) infecting F. asiaticum, the causal agent of wheat fusarium head blight. Phylogenetic analysis further suggested that FoMV3 is a new member of the genus Unuamitovirus within the family Mitoviridae. This is the first report of a new mitovirus associated with F. oxysporum f. sp. melonis.

Antarctica's hidden mycoviral treasures in fungi isolated from mosses: A first genomic approach.

This study investigates the presence of mycoviruses in Antarctic fungi and elucidates their evolutionary relationships. To achieve this, we aligned mycoviral gene sequences with genomes of previously sequenced Antarctic endophytic fungi, made available by our research group and accessible via Joint Genome Institute. Our findings reveal that the most prevalent genetic regions in all endophytic fungi are homologous to Partitiviruses, Baculoviridae, and Phycodnaviridae. These regions display evidence of positive selection pressure, suggesting genetic diversity and the accumulation of nonsynonymous mutations. This phenomenon implies a crucial role for these regions in the adaptation and survival of these fungi in the challenging Antarctic ecosystems. The presence of mycoviruses in Antarctic endophytic fungi may indicate shared survival strategies between the virus and its host, shedding light on their evolutionary dynamics. This study underscores the significance of exploring mycoviruses within endophytic fungi and their contributions to genetic diversity. Future research avenues could delve into the functional implications of these conserved mycoviral genetic regions in Antarctic endophytic fungi, providing a comprehensive understanding of this intriguing association and genomic retention of viral region in fungi.

Sensitivity of Globisporangium ultimum to the fungicide metalaxyl is enhanced by the infection with a toti-like mycovirus.

In recent years, numerous oomycete mycoviruses have been discovered; however, very few studies have focused on their effects on the host oomycete phenotype. In this study, we investigated the impact of toti-like Pythium ultimum RNA virus 2 (PuRV2) infection on the phytopathogenic soil-borne oomycete Globisporangium ultimum, which serves as a model species for Globisporangium and Pythium, specifically the UOP226 isolate in Japan. We generated a PuRV2-free isogenic line through hyphal tip isolation using high-temperature culture and subsequently compared the phenotypic characteristics and gene expression profiles of UOP226 and the PuRV2-free isogenic line. Our findings revealed that the metalaxyl sensitivity of UOP226 was greater than that of the PuRV2-free isogenic line, whereas the mycelial growth rate and colony morphology remained unchanged in the absence of the fungicide. Furthermore, transcriptome analyses using RNA-seq revealed significant downregulation of ABC-type transporter genes, which are involved in fungicide sensitivity, in UOP226. Our results suggest that PuRV2 infection influences the ecology of G. ultimum in agricultural ecosystems where metalaxyl is applied.

Comparative Analysis of Viromes Identified in Multiple Macrofungi.

Macrofungi play important roles in the soil elemental cycle of terrestrial ecosystems. Fungal viruses are common in filamentous fungi, and some of them can affect the growth and development of hosts. However, the composition and evolution of macrofungal viruses are understudied. In this study, ninety strains of Trametes versicolor, Coprinellus micaceus, Amanita strobiliformis, and Trametes hirsuta were collected in China. Four mixed pools were generated by combining equal quantities of total RNA from each strain, according to the fungal species, and then subjected to RNA sequencing. The sequences were assembled, annotated, and then used for phylogenetic analysis. Twenty novel viruses or viral fragments were characterized from the four species of macrofungi. Based on the phylogenetic analysis, most of the viral contigs were classified into ten viral families or orders: Barnaviridae, Benyviridae, Botourmiaviridae, Deltaflexiviridae, Fusariviridae, Hypoviridae, Totiviridae, Mitoviridae, Mymonaviridae, and Bunyavirales. Of these, ambi-like viruses with circular genomes were widely distributed among the studied species. Furthermore, the number and overall abundance of viruses in these four species of macrofungi (Basidiomycota) were found to be much lower than those in broad-host phytopathogenic fungi (Ascomycota: Sclerotinia sclerotiorum, and Botrytis cinerea). By employing metatranscriptomic analysis in this study, for the first time, we demonstrated the presence of multiple mycoviruses in Amanita strobiliformis, Coprinellus micaceus, Trametes hirsute, and Trametes versicolor, significantly contributing to research on mycoviruses in macrofungi.

Characterization of Mycoviruses in Armillaria ostoyae and A. cepistipes in the Czech Republic.

Members of the genus Armillaria are widespread forest pathogens against which effective protection has not yet been developed. Due to their longevity and the creation of large-scale cloning of Armillaria individuals, the use of mycoviruses as biocontrol agents (BCAs) against these pathogens could be an effective alternative. This work describes the detection and characterization of viruses in Armillaria spp. collected in the Czech Republic through the application of stranded total RNA sequencing. A total of five single-stranded RNA viruses were detected in Armillaria ostoyae and A. cepistipes, including viruses of the family Tymoviridae and four viruses belonging to the recently described "ambivirus" group with a circular ambisense genome arrangement. Both hammerhead (HHRz) and hairpin (HpRz) ribozymes were detected in all the ambiviricot sequences. Armillaria viruses were compared through phylogenetic analysis and confirmed their specific host by direct RT-PCR. One virus appears to infect both Armillaria species, suggesting the occurrence of interspecies transmission in nature.

Molecular characterization of the complete genome of a novel ormycovirus infecting the ectomycorrhizal fungus Hortiboletus rubellus.

Advancements in high-throughput sequencing and the development of new bioinformatics tools for large-scale data analysis play a crucial role in uncovering virus diversity and enhancing our understanding of virus evolution. The discovery of the ormycovirus clades, a group of RNA viruses that are phylogenetically distinct from all known Riboviria members and are found in fungi, highlights the value of these tools for the discovery of novel viruses. The aim of this study was to examine viral populations in fungal hosts to gain insights into the diversity, evolution, and classification of these viruses. Here, we report the molecular characterization of a newly discovered ormycovirus, which we have named "Hortiboletus rubellus ormycovirus 1" (HrOMV1), that was found in the ectomycorrhizal fungus Hortiboletus rubellus. The bipartite genome of HrOMV1, whose nucleotide sequence was determined by HTS and RLM-RACE, consists of two RNA segments (RNA1 and RNA2) that exhibit similarity to those of previously studied ormycoviruses in their organization and the proteins they encode. The presence of upstream, in-frame AUG triplets in the 5' termini of both RNA segments suggests that HrOMV1, like certain other ormycoviruses, employs a non-canonical translation initiation strategy. Phylogenetic analysis showed that HrOMV1 is positioned within the gammaormycovirus clade. Its putative RNA-dependent RNA polymerase (RdRp) exhibits sequence similarity to those of other gammaormycovirus members, the most similarity to that of Termitomyces ormycovirus 1, with 33.05% sequence identity. This protein was found to contain conserved motifs that are crucial for RNA replication, including the distinctive GDQ catalytic triad observed in gammaormycovirus RdRps. The results of this study underscore the significance of investigating the ecological role of mycoviruses in mycorrhizal fungi. This is the first report of an ormycovirus infecting a member of the ectomycorrhizal genus Hortiboletus.

Possible Biological Control of Ash Dieback Using the Mycoparasite Hymenoscyphus Fraxineus Mitovirus 2.

Invasive fungal diseases represent a major threat to forest ecosystems worldwide. As the application of fungicides is often unfeasible and not a sustainable solution, only a few other control options are available, including biological control. In this context, the use of parasitic mycoviruses as biocontrol agents of fungal pathogens has recently gained particular attention. Since the 1990s, the Asian fungus Hymenoscyphus fraxineus has been causing lethal ash dieback across Europe. In the present study, we investigated the biocontrol potential of the mitovirus Hymenoscyphus fraxineus mitovirus 2 (HfMV2) previously identified in Japanese populations of the pathogen. HfMV2 could be successfully introduced via co-culturing into 16 of 105 HfMV2-free isolates. Infection with HfMV2 had contrasting effects on fungal growth in vitro, from cryptic to detrimental or beneficial. Virus-infected H. fraxineus isolates whose growth was reduced by HfMV2 showed overall a lower virulence on ash (Fraxinus excelsior) saplings as compared with their isogenic HfMV2-free lines. The results suggest that mycoviruses exist in the native populations of H. fraxineus in Asia that have the potential for biological control of ash dieback in Europe. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Virome analysis of an ectomycorrhizal fungus Suillus luteus revealing potential evolutionary implications.

Suillus luteus is a widespread edible ectomycorrhizal fungus that holds significant importance in both ecological and economic value. Mycoviruses are ubiquitous infectious agents hosted in different fungi, with some known to exert beneficial or detrimental effects on their hosts. However, mycoviruses hosted in ectomycorrhizal fungi remain poorly studied. To address this gap in knowledge, we employed next-generation sequencing (NGS) to investigate the virome of S. luteus. Using BLASTp analysis and phylogenetic tree construction, we identified 33 mycovirus species, with over half of them belonging to the phylum Lenarviricota, and 29 of these viruses were novel. These mycoviruses were further grouped into 11 lineages, with the discovery of a new negative-sense single-stranded RNA viral family in the order Bunyavirales. In addition, our findings suggest the occurrence of cross-species transmission (CST) between the fungus and ticks, shedding light on potential evolutionary events that have shaped the viral community in different hosts. This study is not only the first study to characterize mycoviruses in S. luteus but highlights the enormous diversity of mycoviruses and their implications for virus evolution.

A novel narnavirus isolated from Colletotrichum curcumae strain 780-2T.

The complete genome of a novel mycovirus, Colletotrichum curcumae narnavirus 1 (CcNV1), derived from the phytopathogenic fungus Colletotrichum curcumae strain 780-2T, was sequenced and analyzed. The full sequence of CcNV1 is 3,374 nucleotides in length and contains a single large open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp) of 1,087 amino acids with a molecular mass of 124.2 kDa that shares the closest similarity with that of Monilinia narnavirus H (53.02% identity). RdRp phylogeny analysis showed that CcNV1 is a new member of the proposed genus "Betanarnavirus" within the family Narnaviridae. This is the first report of a novel narnavirus infecting the phytopathogenic fungus C. curcumae, the causal agent of leaf blight of Curcuma wenyujin.

Prevalence and diversity of mycoviruses occurring in Chinese Lentinula edodes germplasm resource.

Incidence and banding patterns of virus-like dsRNA elements in 215 Chinese genetically diverse Lentinula edodes strains collected from wide geographic distribution (or producing areas) were first investigated, and 17 viruses were identified including eight novel viruses. The results revealed a 63.3% incidence of dsRNA elements in the cultivated strains and a 67.2% incidence in the wild strains. A total of 10 distinguishable dsRNAs ranging from 0.6 to 12 kbp and 12 different dsRNA patterns were detected in the positive strains. The molecular information of these dsRNA elements was characterized, and the molecular information of the other 12 different viral sequences with (+) ssRNA genome was revealed in four L. edodes strains with complex dsRNA banding patterns. RT-PCR was also done to verify the five dsRNA viruses and 12 (+) ssRNA ones. The results presented may enrich our understanding of L. edodes virus diversity, and will promote further research on virus-host interactions. IMPORTANCE: Viral infections involve complicated interactions including benign, harmful or possibly beneficial to hosts. Sometimes environment could lead to a transition in lifestyles from persistent to acute, resulting in a disease phenotype. The quality of spawn, such as the vulnerability to infection of viruses, is therefore important for mushroom production. Lentinula edodes, a wood rot basidiomycete fungus, was widely cultivated in the world for its edible and medicinal properties. In this study, the profile of dsRNA elements from Chinese genetically diverse L. edodes strains collected from wide geographic distribution or producing areas was first investigated. The molecular information of the dsRNA elements was characterized. Additionally, 12 different viral sequences with (+) ssRNA genome from four L. edodes strains with complex dsRNA banding patterns were identified. The results presented here will broaden our knowledge about mushroom viruses, and promote further studies of L. edodes production and the interaction between viruses and L. edodes.

Mycovirus Hunting Revealed the Presence of Diverse Viruses in a Single Isolate of the Phytopathogenic Fungus Diplodia seriata From Pakistan.

Diplodia seriata in the family Botryosphaeriaceae is a cosmopolitan phytopathogenic fungus and is responsible for causing cankers, fruit rot and leaf spots on economically important plants. In this study, we characterized the virome of a single Pakistani strain (L3) of D. seriata. Several viral-like contig sequences were obtained via a previously conducted next-generation sequencing analysis. Multiple infection of the L3 strain by eight RNA mycoviruses was confirmed through RT-PCR using total RNA samples extracted from this strain; the entire genomes were determined via Sanger sequencing of RT-PCR and RACE clones. A BLAST search and phylogenetic analyses indicated that these eight mycoviruses belong to seven different viral families. Four identified mycoviruses belong to double-stranded RNA viral families, including Polymycoviridae, Chrysoviridae, Totiviridae and Partitiviridae, and the remaining four identified mycoviruses belong to single-stranded RNA viral families, i.e., Botourmiaviridae, and two previously proposed families "Ambiguiviridae" and "Splipalmiviridae". Of the eight, five mycoviruses appear to represent new virus species. A morphological comparison of L3 and partially cured strain L3ht1 suggested that one or more of the three viruses belonging to Polymycoviridae, "Splipalmiviridae" and "Ambiguiviridae" are involved in the irregular colony phenotype of L3. To our knowledge, this is the first report of diverse virome characterization from D. seriata.

A Capsidless Virus Is trans-Encapsidated by a Bisegmented Botybirnavirus.

RNA viruses usually have linear genomes and are encapsidated by their own capsids. Here, we newly identified four mycoviruses and two previously reported mycoviruses (a fungal reovirus and a botybirnavirus) in the hypovirulent strain SCH941 of Sclerotinia sclerotiorum. One of the newly discovered mycoviruses, Sclerotinia sclerotiorum yadokarivirus 1 (SsYkV1), with a nonsegmented positive-sense single-stranded RNA (+ssRNA) genome, was molecularly characterized. SsYkV1 is 5,256 nucleotides (nt) in length, excluding the poly(A) structure, and has a large open reading frame that putatively encodes a polyprotein with the RNA-dependent RNA polymerase (RdRp) domain and a 2A-like motif. SsYkV1 was phylogenetically positioned into the family Yadokariviridae and was most closely related to Rosellinia necatrix yadokarivirus 2 (RnYkV2), with 40.55% identity (78% coverage). Although SsYkV1 does not encode its own capsid protein, the RNA and RdRp of SsYkV1 are trans-encapsidated in virions of Sclerotinia sclerotiorum botybirnavirus 3 (SsBV3), a bisegmented double-stranded RNA (dsRNA) mycovirus within the genus Botybirnavirus. In this way, SsYkV1 likely replicates inside the heterocapsid comprised of the SsBV3 capsid protein, like a dsRNA virus. SsYkV1 has a limited impact on the biological features of S. sclerotiorum. This study represents an example of a yadokarivirus trans-encapsidated by an unrelated dsRNA virus, which greatly deepens our knowledge and understanding of the unique life cycles of RNA viruses. IMPORTANCE RNA viruses typically encase their linear genomes in their own capsids. However, a capsidless +ssRNA virus (RnYkV1) highjacks the capsid of a nonsegmented dsRNA virus for the trans-encapsidation of its own RNA and RdRp. RnYkV1 belongs to the family Yadokariviridae, which already contains more than a dozen mycoviruses. However, it is unknown whether other yadokariviruses except RnYkV1 are also hosted by a heterocapsid, although dsRNA viruses with capsid proteins were detected in fungi harboring yadokarivirus. It is noteworthy that almost all presumed partner dsRNA viruses of yadokariviruses belong to the order Ghabrivirales (most probably a totivirus or toti-like virus). Here, we found a capsidless +ssRNA mycovirus, SsYkV1, from hypovirulent strain SCH941 of S. sclerotiorum, and the RNA and RdRp of this mycovirus are trans-encapsidated in virions of a bisegmented dsRNA virus within the free-floating genus Botybirnavirus. Our results greatly expand our knowledge of the unique life cycles of RNA viruses.

Four Novel Mycoviruses from the Hypovirulent Botrytis cinerea SZ-2-3y Isolate from Paris polyphylla: Molecular Characterisation and Mitoviral Sequence Transboundary Entry into Plants.

A hypovirulent SZ-2-3y strain isolated from diseased Paris polyphylla was identified as Botrytis cinerea. Interestingly, SZ-2-3y was coinfected with a mitovirus, two botouliviruses, and a 3074 nt fusarivirus, designated Botrytis cinerea fusarivirus 8 (BcFV8); it shares an 87.2% sequence identity with the previously identified Botrytis cinerea fusarivirus 6 (BcFV6). The full-length 2945 nt genome sequence of the mitovirus, termed Botrytis cinerea mitovirus 10 (BcMV10), shares a 54% sequence identity with Fusarium boothii mitovirus 1 (FbMV1), and clusters with fungus mitoviruses, plant mitoviruses and plant mitochondria; hence BcMV10 is a new Mitoviridae member. The full-length 2759 nt and 2812 nt genome sequences of the other two botouliviruses, named Botrytis cinerea botoulivirus 18 and 19 (BcBoV18 and 19), share a 40% amino acid sequence identity with RNA-dependent RNA polymerase protein (RdRp), and these are new members of the Botoulivirus genus of Botourmiaviridae. Horizontal transmission analysis showed that BcBoV18, BcBoV19 and BcFV8 are not related to hypovirulence, suggesting that BcMV10 may induce hypovirulence. Intriguingly, a partial BcMV10 sequence was detected in cucumber plants inoculated with SZ-2-3y mycelium or pXT1/BcMV10 agrobacterium. In conclusion, we identified a hypovirulent SZ-2-3y fungal strain from P. polyphylla, coinfected with four novel mycoviruses that could serve as potential biocontrol agents. Our findings provide evidence of cross-kingdom mycoviral sequence transmission.

Metagenomics Analysis of the Wheat Virome Identifies Novel Plant and Fungal-Associated Viral Sequences.

Wheat viruses including wheat streak mosaic virus, Triticum mosaic virus, and barley yellow dwarf virus cost substantial losses in crop yields every year. Although there have been extensive studies conducted on these known wheat viruses, currently, there is limited knowledge about all components of the wheat (Triticum aestivum L.) virome. Here, we determined the composition of the wheat virome through total RNA deep sequencing of field-collected leaf samples. Sequences were de novo assembled after removing the host reads, and BLASTx searches were conducted. In addition to the documented wheat viruses, novel plant and fungal-associated viral sequences were identified. We obtained the full genome sequence of the first umbra-like associated RNA virus tentatively named wheat umbra-like virus in cereals. Moreover, a novel bi-segmented putative virus tentatively named wheat-associated vipovirus sharing low but significant similarity with both plant and fungal-associated viruses was identified. Additionally, a new putative fungal-associated tobamo-like virus and novel putative Mitovirus were discovered in wheat samples. The discovery and characterization of novel viral sequences associated with wheat is important to determine if these putative viruses may pose a threat to the wheat industry or have the potential to be used as new biological control agents for wheat pathogens either as wild-type or recombinant viruses.

Omnipresence of Partitiviruses in Rice Aggregate Sheath Spot Symptom-Associated Fungal Isolates from Paddies in Thailand.

Partitiviruses are one of the most prevalent double-stranded RNA viruses that have been identified mostly in filamentous fungi and plants. Partitiviruses generally infect host fungi asymptomatically but infrequently exert significant effect(s) on morphology and virulence, thus being considered a potential source of biological control agents against pathogenic fungi. In this study, we performed a screening for mycoviruses of a collection of Thai isolates of rice fungal pathogen Rhizoctonia oryzae-sativae, a causal agent of rice aggregated sheath spot disease. As a result, 36% of tested isolates carried potentially viral double-stranded RNAs with sizes ranging from 2 to 3 kbp. By conventional cDNA library construction and RNA-seq, we determined six new alphapartitiviruses that infected three isolates: tentatively named Rhizoctonia oryzae-sativae partitivirus 1 to 6 (RosPV1-6). Furthermore, RT-PCR detection of each virus revealed their omnipresent nature in different R. oryzae-sativae isolates. Although virus-curing of basidiomycetous fungi is generally difficult, our repeated attempts successfully obtained virus-free (for RosPV1, RosPV2, and uncharacterized partitiviruses), isogenic strain of R. oryzae-sativae TSS190442. The virus-cured strain showed slightly faster colony growth on the synthetic media and severe symptom development on the rice sheath compared to its virus-infected counterpart. Overall, this study shed light on the distribution of partitiviruses in R. oryzae-sativae in a paddy environment and exemplified a virus-curing protocol that may be applicable for other basidiomycetous fungi.