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Talaromyces spp. have a worldwide distribution, are ecologically diverse and have been isolated from numerous different substrates. Talaromyces spp. are considered biotechnologically important due to their ability to produce a range of enzymes and pigments. Talaromyces pinophilus, belonging to genus Talaromyces and family Trichocomaceae, is known for producing several important bioactive metabolites. Here we report the isolation and characterisation of a partitivirus from T. pinophilus which we have nominated Talaromyces pinophilus partitivirus-1 (TpPV-1). TpPV-1 possesses a genome consisting of three double stranded (ds) RNA segments i.e., dsRNAs1-3, 1824 bp, 1638 bp and 1451 bp respectively, which are encapsidated in icosahedral particles 35 nm in diameter. Both dsRNA1 and dsRNA2 contain a single open reading frame (ORF) encoding respectively a 572 amino acid (aa) protein of 65 kDa and a 504 aa protein of 50 kDa. The third segment (dsRNA3) is potentially a satellite RNA. Phylogenetic analysis revealed that the TpPV-1 belongs to the family Partitiviridae in the proposed genus Zetapartitivirus. TpPV-1 infection decreases the mycelial growth rate of the host fungus and alters pigmentation as indicated by time course experiments performed on a range of different solid media comparing virus-infected and virus-free isogenic lines. This is the first report of mycovirus infection in T. pinophilus and may provide insights into understanding the effect of the mycovirus on the production of enzymes and pigments by the host fungus., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Importance: A novel botybirnavirus, infecting the tea plant pathogen Didymella theifolia and tentatively named Didymella theifolia botybirnavirus 1 (DtBRV1), together with an additional double-stranded RNA (dsRNA), was characterized. DtBRV1 comprises two dsRNAs (1 and 2) encapsidated in isometric virions, while dsRNA3 is a satellite. The satellite represents a unique specimen since it contains a duplicated region and has high similarity to the two botybirnavirus dsRNAs, supporting the notion that it most likely originated from a deficient genomic component. The biological characteristics of DtBRV1 were further determined. With their unique molecular traits, DtBRV1 and its related dsRNA expand our understanding of virus diversity, taxonomy, and evolution., Competing Interests: The authors declare no conflict of interest.

Mycoviruses are widely present in all major groups of fungi but those in entomopathogenic Metarhizium spp. remain understudied. In this investigation, a novel double-stranded (ds) RNA virus is isolated from Metarhizium majus and named Metarhizium majus partitivirus 1 (MmPV1). The complete genome sequence of MmPV1 comprises two monocistronic dsRNA segments (dsRNA 1 and dsRNA 2), which encode an RNA-dependent RNA polymerase (RdRp) and a capsid protein (CP), respectively. MmPV1 is classified as a new member of the genus Gammapartitivirus in the family Partitiviridae based on phylogenetic analysis. As compared to an MmPV1-free strain, two isogenic MmPV1-infected single-spore isolates were compromised in terms of conidiation, and tolerance to heat shock and UV-B irradiation, while these phenotypes were accompanied by transcriptional suppression of multiple genes involved in conidiation, heat shock response and DNA damage repair. MmPV1 attenuated fungal virulence since infection resulted in reduced conidiation, hydrophobicity, adhesion, and cuticular penetration. Additionally, secondary metabolites were significantly altered by MmPV1 infection, including reduced production of triterpenoids, and metarhizins A and B, and increased production of nitrogen and phosphorus compounds. However, expression of individual MmPV1 proteins in M. majus had no impact on the host phenotype, suggesting insubstantive links between defective phenotypes and a single viral protein. These findings indicate that MmPV1 infection decreases M. majus fitness to its environment and its insect-pathogenic lifestyle and environment through the orchestration of the host conidiation, stress tolerance, pathogenicity, and secondary metabolism., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

A new double-stranded (ds) RNA mycovirus has been identified in isolate Ds752-1 of the phytopathogenic fungus Dothistroma septosporum, the causal agent of Dothistroma needle blight, also known as red band needle blight or pine needle blight. Dothistroma septosporum chrysovirus 1 (DsCV-1) is a new member of the genus Alphachrysovirus in the family Chrysoviridae. The DsCV-1 genome comprises four dsRNA elements designated 1, 2, 3, and 4 from largest to smallest. dsRNA1 encodes an RNA-dependent RNA polymerase (RdRP) that is most similar to the RdRP of Erysiphe necator associated chrysovirus 3. dsRNA2 potentially encodes two hypothetical proteins, one of which is small and has no homology to known proteins, and one of which is large with significant sequence similarity to the alphachryso-P3 of other alphachrysoviruses. dsRNA3 and dsRNA4 encode a coat protein (CP) and a putative cysteine protease, respectively. This is the first report of a mycovirus infecting the fungus D. septosporum, and DsCV-1 is one of three Chrysoviridae family members found to possess genomic dsRNAs potentially encoding more than one protein., (© 2023. The Author(s).)

Infection with Aspergillus fumigatus polymycovirus 1 (AfuPmV-1) weakens the resistance of biofilms of common A. fumigatus reference strain Af293 in intermicrobial competition with Pseudomonas aeruginosa , and sensitizes A. fumigatus for antifungal effects of nikkomycin Z. We compared the sensitivity of two virus-infected (VI) and one virus-free (VF) Af293 strains to hypertonic salt. Salt stress impairs the growth of VI and VF at all times; VF control growth always exceeds VI, and VF growth in salt always exceeds VI. Since VF growth exceeds VI in the presence and absence of salt, we also examined growth in salt as a percentage of control growth. Initially, as a percentage of control, VI exceeded VF, but at 120 h VF began to exceed VI consistently even by this measure; thus, at that time the growth of VF in salt surges in relation to control growth, or, alternatively, its growth in salt persists compared to the relative inhibition of VI. In summary, virus infection impairs the response of A. fumigatus to several different stresses, including hypertonic salt.

Infection with Aspergillus fumigatus polymycovirus 1 (AfuPmV-1) weakens resistance of Aspergillus fumigatus common reference strain Af293 biofilms in intermicrobial competition with Pseudomonas aeruginosa . We compared the sensitivity of two infected and one virus-free Af293 strains to antifungal drugs. All three were comparably sensitive to drugs affecting fungal membranes (voriconazole, amphotericin) or cell wall glucan synthesis (micafungin, caspofungin). In contrast, forming biofilms of virus-free Af293 were much more resistant than AfuPmV-1-infected Af293 to nikkomycin Z (NikZ), a drug inhibiting chitin synthase. The IC50 for NikZ on biofilms was between 3.8 and 7.5 µg/mL for virus-free Af293 and 0.94-1.88 µg/mL for infected strains. The IC50 for the virus-free A. fumigatus strain 10AF was ~2 µg/mL in most experiments. NikZ also modestly affected the planktonic growth of infected Af293 more than the virus-free strain (MIC 50%, 2 and 4 µg/mL, respectively). Virus-free Af293 biofilm showed increased metabolism, and fungus growing as biofilm or planktonically showed increased growth compared to infected; these differences do not explain the resistance of the virus-free fungus to NikZ. In summary, AfuPmV-1 infection sensitized A. fumigatus to NikZ, but did not affect response to drugs commonly used against A. fumigatus infection. Virus infection had a greater effect on NikZ inhibition of biofilm than planktonic growth.

The family Hadakaviridae , including the genus Hadakavirus , accommodates capsidless viruses with a 10- or 11-segmented positive-sense (+) RNA genome. Currently known hosts are ascomycetous filamentous fungi. Although phylogenetically related to polymycovirids with a segmented double-stranded RNA genome and certain encapsidated picorna-like viruses, hadakavirids are distinct in their lack of a capsid ('hadaka' means naked in Japanese) and their consequent inability to be pelleted by conventional ultracentrifugation; they show ribonuclease susceptibility in host tissue homogenates. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Hadakaviridae, which is available at ictv.global/report/hadakaviridae.

The family Yadokariviridae , with the genera Alphayadokarivirus and Betayadokarivirus , includes capsidless non-segmented positive-sense (+) RNA viruses that hijack capsids from phylogenetically distant double-stranded RNA viruses. Yadokarivirids likely replicate inside the hijacked heterocapsids using their own RNA-directed RNA polymerase, mimicking dsRNA viruses despite their phylogenetic placement in a (+) RNA virus lineage. Yadokarivirids can have negative or positive impacts on their host fungi, through interactions with the capsid donor dsRNA viruses. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) report on the family Yadokariviridae , which is available at ictv.global/report/yadokariviridae.

In this study, a novel positive-sense single-stranded RNA (+ssRNA) mycovirus, tentatively named Colletotrichum fructicola RNA virus 1 (CfRV1), was identified in the phytopathogenic fungus Colletotrichum fructicola . CfRV1 has seven genomic components, encoding seven proteins from open reading frames (ORFs) flanked by highly conserved untranslated regions (UTRs). Proteins encoded by ORFs 1, 2, 3, 5, and 6 are more similar to the putative RNA-dependent RNA polymerase (RdRp), hypothetical protein (P2), methyltransferase, and two hypothetical proteins of Hadaka virus 1 (HadV1), a capsidless 10- or 11-segmented +ssRNA virus, while proteins encoded by ORFs 4 and 7 showed no detectable similarity to any known proteins. Notably, proteins encoded by ORFs 1 to 3 also share considerably high similarity with the corresponding proteins of polymycoviruses. Phylogenetic analysis conducted based on the amino acid sequence of CfRV1 RdRp and related viruses placed CfRV1 and HadV1 together in the same clade, close to polymycoviruses and astroviruses. CfRV1-infected C. fructicola strains demonstrate a moderately attenuated growth rate and virulence compared to uninfected isolates. CfRV1 is capsidless and potentially encapsulated in vesicles inside fungal cells, as revealed by transmission electron microscopy. CfRV1 and HadV1 are +ssRNA mycoviruses closely related to polymycoviruses and astroviruses, represent a new linkage between +ssRNA viruses and the intermediate double-stranded RNA (dsRNA) polymycoviruses, and expand our understanding of virus diversity, taxonomy, evolution, and biological traits. IMPORTANCE A scenario proposing that dsRNA viruses evolved from +ssRNA viruses is still considered controversial due to intergroup knowledge gaps in virus diversity. Recently, polymycoviruses and hadakaviruses were found as intermediate dsRNA and +ssRNA stages, respectively, between +ssRNA and dsRNA viruses. Here, we identified a novel +ssRNA mycovirus, Colletotrichum fructicola RNA virus 1 (CfRV1), isolated from Colletotrichum fructicola in China. CfRV1 is phylogenetically related to the 10- or 11-segmented Hadaka virus 1 (HadV1) but consists of only seven genomic segments encoding two novel proteins. CfRV1 is naked and may be encapsulated in vesicles inside fungal cells, representing a potential novel lifestyle for multisegmented RNA viruses. CfRV1 and HadV1 are intermediate +ssRNA mycoviruses in the linkage between +ssRNA viruses and the intermediate dsRNA polymycoviruses and expand our understanding of virus diversity, taxonomy, and evolution.

Members of the family Polymycoviridae are small viruses with multi-segmented and non-conventionally encapsidated double-stranded (ds) RNA genomes. Typically, polymycoviruses have four genomic segments, although some have up to eight. The genus Polymycovirus includes several species whose members infect fungi (ascomycetes and basidiomycetes), and oomycetes, altering host morphology, sporulation, growth and virulence. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Polymycoviridae, which is available at ictv.global/report/polymycoviridae.

Nowadays, the focus of mycovirology research has expanded from plant pathogenic fungi and mycovirus mediated hypovirulence to include insect and human pathogenic fungi together with a range of mycovirus mediated phenotypes, such as hypervirulence, control of endophytic traits, regulation of metabolite production and drug resistance. In fungus-mycovirus-environmental interactions, the environment and both abiotic and biotic factors play crucial roles in whether and how mycovirus mediated phenotypes are manifest. Mycovirus infections result in alterations in the host transcriptome profile, via protein-protein interactions and triggering of antiviral RNA silencing in the fungus. These alterations, in combination with the environmental factors, may result in desirable phenotypic traits for the host, for us and in some cases for both., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Fungi are generally thought to live in host plants with a single lifestyle, being parasitism, commensalism, or mutualism. The former, known as phytopathogenic fungi, cause various plant diseases that result in significant losses every year; while the latter, such as endophytic fungi, can confer fitness to the host plants. It is unclear whether biological factors can modulate the parasitic and mutualistic traits of a fungus. In this study, we isolated and characterized a mycovirus from an endophytic strain of the fungus Pestalotiopsis theae, a pathogen of tea (Camellia sinensis). Based on molecular analysis, we tentatively designated the mycovirus as Pestalotiopsis theae chrysovirus-1 (PtCV1), a novel member of the family Chrysoviridae, genus Alphachrysovirus. PtCV1 has four double-stranded (ds) RNAs as its genome, ranging from 0.9 to 3.4 kbp in size, encapsidated in isometric particles. PtCV1 significantly reduced the growth rates of its host fungus in vitro (ANOVA; P-value < 0.001) and abolished its virulence in planta (ANOVA; P-value < 0.001), converting its host fungus to a non-pathogenic endophyte on tea leaves, while PtCV1-free isolates were highly virulent. Moreover, the presence of PtCV1 conferred high resistance to the host plants against the virulent P. theae strains. Here we report a mycovirus that modulates endophytic and phytopathogenic fungal traits and provides an alternative approach to biological control of plant diseases caused by fungi.

A Portuguese isolate of Aspergillus fumigatus was found to contain three double-stranded (ds) RNA elements ranging in size from 1.1 to 1.8 kbp and comprising the genome of a strain of Aspergillus fumigatus partitivirus 1 (AfuPV-1) previously thought to contain only the two largest dsRNA elements. The sequence of the smallest dsRNA element is described here, completing the sequence of the AfuPV-1 genome. Sequence analysis of the element revealed an open reading frame encoding a protein of unknown function similar in size and distantly related to elements previously identified in other members of the family Partitiviridae.

Members of the family Chrysoviridae are isometric, non-enveloped viruses with segmented, linear, dsRNA genomes. There are 3-7 genomic segments, each of which is individually encapsidated. Chrysoviruses infect fungi, plants and possibly insects, and may cause hypovirulence in their fungal hosts. Chrysoviruses have no known vectors and lack an extracellular phase to their replication cycle; they are transmitted via intracellular routes within an individual during hyphal growth, in asexual or sexual spores, or between individuals via hyphal anastomosis. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the family Chrysoviridae , which is available at ictv.global/report/chrysoviridae.

An isolate of the entomopathogenic fungus Beauveria bassiana was found to contain five double-stranded (ds) RNA elements ranging from 1.5 to more than 3 kbp. The complete sequence of the largest dsRNA element is described here. Analysis of the RdRp nucleotide sequence reveals its similarity to unclassified dsRNA elements, such as Alternaria longipes dsRNA virus 1, and its distant relationship to the RNA-dependent RNA polymerases of members of the family Partitiviridae.

Nidovirales , which accommodates viruses with the largest RNA genomes, includes the notorious coronaviruses; however, the evolutionary route for nidoviruses is not well understood. We have characterized a positive-sense (+) single-stranded (ss) RNA mycovirus, R hizoctonia s olani h ypo v irus 2 (RsHV2), from the phytopathogenic fungus Rhizoctonia solani. RsHV2 has the largest RNA genome size of 22,219 nucleotides, excluding the poly(A) tail, in all known mycoviruses, and contains two open reading frames (ORF1 and ORF2). ORF1 encodes a protein of 2,009 amino acid (aa) that includes a conserved helicase domain belonging to helicase superfamily I (SFI). In contrast, ORF2 encodes a polyprotein of 4459 aa containing the hallmark genes of hypoviruses. The latter includes a helicase belonging to SFII. Following phylogenetic analysis, the ORF1-encoded helicase (Hel1) unexpectedly clustered in an independent evolutionary branch together with nidovirus helicases, including coronaviruses, and bacteria helicases. Thus, Hel1 presence indicates the occurrence of horizontal gene transfer between viruses and bacteria. These findings also suggest that RsHV2 is most likely a recombinant arising between hypoviruses and nidoviruses. [ABSTRACT FROM AUTHOR]

The entomopathogenic fungus Beauveria bassiana has a wide host range and is used as a biocontrol agent against arthropod pests. Mycoviruses have been described in phytopathogenic fungi while in entomopathogenic fungi their presence has been reported only rarely. Here we show that 21.3% of a collection of B. bassiana isolates sourced from worldwide locations, harbor dsRNA elements. Molecular characterization of these elements revealed the prevalence of mycoviruses belonging to the Partitiviridae and Totiviridae families, the smallest reported virus to date, belonging to the family Narnaviridae, and viruses unassigned to a family or genus. Of particular importance is the discovery of members of a newly proposed family Polymycoviridae in B. bassiana. Polymycoviruses, previously designated as tetramycoviruses, consist of four non-conventionally encapsidated capped dsRNAs. The presence of additional non-homologous genomic segments in B. bassiana polymycoviruses and other fungi illustrates the unprecedented dynamic nature of the viral genome. Finally, a comparison of virus-free and virus-infected isogenic lines derived from an exemplar B. bassiana isolate revealed a mild hypervirulent effect of mycoviruses on the growth of their host isolate and on its pathogenicity against the greater wax moth Galleria mellonella, highlighting for the first time the potential of mycoviruses as enhancers of biocontrol agents. [ABSTRACT FROM AUTHOR]

In this study, a novel positive-sense single-stranded RNA (1ssRNA) mycovirus, tentatively named Colletotrichum fructicola RNA virus 1 (CfRV1), was identified in the phytopathogenic fungus Colletotrichum fructicola. CfRV1 has seven genomic components, encoding seven proteins from open reading frames (ORFs) flanked by highly conserved untranslated regions (UTRs). Proteins encoded by ORFs 1, 2, 3, 5, and 6 are more similar to the putative RNA-dependent RNA polymerase (RdRp), hypothetical protein (P2), methyltransferase, and two hypothetical proteins of Hadaka virus 1 (HadV1), a capsidless 10- or 11-segmented 1ssRNA virus, while proteins encoded by ORFs 4 and 7 showed no detectable similarity to any known proteins. Notably, proteins encoded by ORFs 1 to 3 also share considerably high similarity with the corresponding proteins of polymycoviruses. Phylogenetic analysis conducted based on the amino acid sequence of CfRV1 RdRp and related viruses placed CfRV1 and HadV1 together in the same clade, close to polymycoviruses and astroviruses. CfRV1-infected C. fructicola strains demonstrate a moderately attenuated growth rate and virulence compared to uninfected isolates. CfRV1 is capsidless and potentially encapsulated in vesicles inside fungal cells, as revealed by transmission electron microscopy. CfRV1 and HadV1 are 1ssRNA mycoviruses closely related to polymycoviruses and astroviruses, represent a new linkage between 1ssRNA viruses and the intermediate double-stranded RNA (dsRNA) polymycoviruses, and expand our understanding of virus diversity, taxonomy, evolution, and biological traits. [ABSTRACT FROM AUTHOR]