Colletotrichum falcatum is a major fungal pathogen responsible for severe disease in sugarcane. Here, we report the complete genomic characterization of a novel mycovirus infecting C. falcatum, designated Colletotrichum falcatum victorivirus 1 (CfVV1). The CfVV1 genome is 4,906 base pairs (bp) long and comprises two open reading frames encoding a capsid protein (CP) and an RNA-dependent RNA polymerase (RdRP), overlapping at an AUGA motif. The predicted proteins share ca. 70

Oilseed rape (Brassica napus) production faces a wide range of biotic threats. Pests typically pose a greater threat than diseases to oilseed rape, yet both vary considerably across the major cultivating regions. Management strategies often rely heavily on the use of chemical pesticides which may have harmful effects on the environment, thus developing new forms of biological control is key to future oilseed rape security. Mycoviruses are viruses that infect fungi, altering phenotypes of their host upon infection and are emerging as potential biocontrol agents. In plant pathogenic fungi, mycovirus-induced hypovirulence can be used to reduce disease severity and in entomopathogenic fungi (EPF), mycovirus-induced hypervirulence can enhance effectiveness of EPF-based pest control. Mycoviruses of some pathogenic fungi, like Sclerotinia sclerotiorum, have been explored extensively and present many candidates for biocontrol. Viral diversity of other pathogenic fungi remains poorly understood and therefore presents an opportunity for new discoveries. In this review, we summarise existing mycoviruses of pathogenic fungi relevant to oilseed rape, highlighting those species with potential to control their respective pests/diseases. Furthermore, recent advancements in mycovirus research and the current challenges facing mycovirus-based applications are also discussed.

Mycoviruses can induce phenotypic and physiological changes in their fungal hosts, making them valuable biological resources. To harness this potential, it is crucial to gather comprehensive information on their distribution patterns, genomic and structural characteristics, and interactions with host fungi. In this study, we screened 64 ascomycete isolates collected from various soil environments in Korea to detect the presence of double-stranded RNA (dsRNA) elements. We identified dsRNA bands in three of these isolates. Among them, we determined the complete genome sequence of a bipartite dsRNA virus found in Cladosporium anthropophilum. Phylogenetic analyses based on the RNA-dependent RNA polymerase (RdRP) and capsid protein (CP) sequences indicated that this virus belongs to the genus Gammapartitivirus within the family Partitiviridae. Comparative sequence analyses suggested that this virus is best classified as a new isolate of Cladosporium cladosporioides partitivirus 1, which we designated as Cladosporium cladosporioides partitivirus 1 isolate IPBL11 (CcPV1-IPBL11).

In the present study, a Pakistani isolate of a known chrysovirus was identified in Penicillium rubens strain S25 tentatively named as Penicillium rubens chrysovirus 1 (PrCV1). PrCV1 has five genomic segments, ranging from 0.5 to 3.7 kbp in length. Analysis of the RNA-dependent RNA polymerase (RdRP) amino acid sequence revealed a 99.28% identity with the genome of Penicillium chrysogenum chrysovirus, suggesting a close evolutionary relationship. Notably, a fifth segment, absent in P. chrysogenum, was identified and is described here for the first time in P. rubens. Sequence analysis showed that this fifth segment is 514 bp in length and has a 5'-terminus identical to the other four segments but it differs in the Box-1 region and lacks the characteristic CAA repeats.

Beauveria bassiana is an entomopathogenic ascomycete widely utilized in biological pest control. However, its effectiveness is often limited by low conidiation rates, sensitivity to environmental stresses, and delayed insecticidal activity. In this study, we identify and characterize a mycovirus, Beauveria bassiana polymycovirus 4-2 (BbPmV4-2), which markedly enhances the fitness and may modulate virulence of its fungal host. BbPmV4-2 comprises eight double-stranded RNA segments, among which three are unique and have not been previously detected in related mycoviruses. Infection with BbPmV4-2 nearly doubles conidial yields and upregulates key conidiation-related genes, facilitating enhanced dispersal of both the host fungus and the mycovirus itself. Additionally, BbPmV4-2 infected strains exhibit increased tolerance to ultraviolet (UV) irradiation and elevated temperatures, and may also exhibit increased virulence against the greater wax moth, Galleria mellonella. The potentially increased virulence is attributed to increased conidial hydrophobicity, adhesion, and cuticle penetration capabilities. Functional analysis reveals that the viral open reading frame ORF5 plays a critical role in conferring hypervirulence and stress tolerance by interacting with host proteins BbGAP1, a GPI-anchored membrane protein, and BbSDU1, a deubiquitinating enzyme. These interactions elucidate a molecular mechanism by which a mycovirus that enhances environmental adaptability and potentially influences host pathogenicity. Our findings provide significant insights into mycovirus-host interactions and suggest potential strategies for optimizing biological pest control applications.

Mycoviruses are widely distributed among different groups of filamentous fungi. An awareness of infections caused by mycoviruses was highlighted in the 1980s and 1990s, when the impact of these agents on phenotypes of agriculturally and medically important fungi was reported. However, for entomopathogenic fungi, mycovirus research has only expanded significantly in the last 15 years. Due to the agricultural importance of these fungi, reflected in their use at the forefront of biological control strategies, recent studies have extensively described novel viruses and their effects on their hosts in terms of altered morphological, phenotypical, and ecological characteristics. To summarise the historical progress of mycovirology and recent discoveries, here we describe the state of the art in the study of mycoviruses associated with entomopathogenic fungi. We have limited the review to the occurrence of mycoviruses in fungi of the genera Beauveria, Cordyceps, Entomophthora, Metarhizium, and Trichoderma and have compiled an inventory of the viruses reported to infect these entomopathogenic genera, as well as a comprehensive review of the biological effects described with respect to infection by mycoviruses in fungi that are relevant to the biological control of insects. Finally, we have outlined possible research scenarios in the light of recent discoveries in the field of mycovirology, such as the use of mycoviruses as virulence modulating factors: the main character sought in biological pest control.

Leptosphaeria biglobosa is a phytopathogenic ascomycete of Brassica napus that causes phoma stem canker/blackleg. A new double-stranded RNA (dsRNA) mycovirus from this fungus has been fully characterized. The virus genome has five dsRNA segments, ranging in length from 1,180 bp to 2,402 bp. Each dsRNA has a single open reading frame flanked by 5′ and 3′ untranslated regions. The proteins encoded by dsRNAs 1 and 3, an RNA-dependent RNA polymerase (RdRP) and a methyltransferase, respectively, have significant similarity to those of Plasmopara viticola lesion associated polymycovirus 1. The proline-alanine-serine-rich protein encoded by dsRNA 5 is similar to that of Erysiphe necator associated polymycovirus 1. The proteins encoded by dsRNAs 2 and 4 have significant similarity to those of a mycovirus identified in Alternaria sp. FA0703. Phylogenetic analysis based on RdRP sequences showed that this virus clusters with members of the family Polymycoviridae. Based on these observations, this virus, which we have named "Leptosphaeria biglobosa polymycovirus 1", should be classified as a member of the family Polymycoviridae. This is the first report of a polymycovirus in L. biglobosa.

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Mycoviral infection can either be asymptomatic or have marked effects on fungal hosts, influencing them either positively or negatively. To fully understand the effects of mycovirus infection on the fungal host, transcriptomic profiling of four Beauveria bassiana isolates, including EABb 92/11-Dm that harbors mycoviruses, was performed 48 h following infection of Tenebrio molitor via topical application or injection. Genes that participate in carbohydrate assimilation and transportation, and those essential for fungal survival and oxidative stress tolerance, calcium uptake, and iron uptake, were found to be overexpressed in the virus-infected isolate during the mid-infection stage. Mycotoxin genes encoding bassianolide and oosporein were switched off in all isolates. However, beauvericin, a mycotoxin capable of inducing oxidative stress at the molecular level, was expressed in all four isolates, indicating an important contribution to virulence against T. molitor. These observations suggest that detoxification of immune-related (oxidative) defenses and nutrient scouting, as mediated by these genes, occurs in mid-infection during the internal growth phase. Consequently, we observe a symbiotic relationship between mycovirus and fungus that does not afflict the host; on the contrary, it enhances the expression of key genes leading to a mycovirus-mediated hypervirulence effect.

The number of documented viruses that infect fungi has increased during the past few decades. Mycoviruses that infect plant pathogenic fungi are the main focus of mycoviral research since some of them have the capacity to cause hypovirulence to their host and hence function as potential biocontrol agents. This article provides a comprehensive overview of mycoviruses infecting plant pathogenic fungus Rosellinia necatrix causing white root rot, including the prevalence of their occurrence, their taxonomic classification, their genomic organization and structure, impacts on their fungal host in terms of phenotype in general and virulence in particular, and their ecological interactions including transmission. The white root rot fungus is found to harbor diverse mycoviruses with double-stranded and positive-sense single-stranded RNA genomes from different families, including Spinareoviridae, Megabirnaviridae, Partitiviridae, Quadriviridae, Pseudototiviridae, Endornaviridae, Fusariviridae, Yadokariviridae, Hypoviridae, Fusagraviridae and Megatotiviridae. Some of these mycoviruses studied in R. necatrix or a heterologous host Cryphonectria parasitica revealed interesting virus-host interplays and appear to be promising agents for biological control applications against white root rot.

Mycoviruses possess a potential role for biological control due to their ability to reduce both virulence and vegetative growth in some phytopathogenic fungi. However, mycoviruses that enhance fungal pathogenicity have been poorly studied and characterized. In this study, a novel double-stranded RNA (dsRNA) fungal virus, tentatively named Sinodiscula camellicola partitivirus 1 (ScPV1), was identified in the phytopathogenic fungus Sinodiscula camellicola, isolated from tea leaves. ScPV1 possesses two genomic components of 1,835 bp and 1,697 bp in length, each containing an open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRP) and coat protein (CP), respectively, as confirmed by mass spectrometry. Phylogenetic analysis of the amino acid sequences of the RdRPs from ScPV1 and related mycoviruses placed ScPV1 within a newly proposed genus, Epsilonpartitivirus, in the family Partitiviridae. The virus was purified using ultracentrifugation, and transmission electron microscopy revealed that ScPV1 dsRNA genomes are encapsidated in virus particles ca. 31 nm in size, ranging from 24.9 to 36.8 nm, together with the RdRP protein, which was of an unexpected size. Transfection with purified virions generated transfectants with significantly reduced growth rates but with increased virulence, indicating that ScPV1 confers unusual effects on its host fungus. This finding represents a significant advancement in understanding the complex interactions between mycoviruses and their host fungi. IMPORTANCE:Here, we identified a novel partitivirus, tentatively named Sinodiscula camellicola partitivirus 1 (ScPV1), marking the first report of a partitivirus from a phytopathogenic fungus infecting tea plants. ScPV1 is characterized by possession of two dsRNA genomic components encapsidated in particles of varying sizes, along with an RNA-dependent RNA polymerase protein of an expected size, which contained some unique amino acids, indicating its distinct molecular and morphological traits. Biological tests on transfectants generated following protoplast infection with purified virions demonstrated that ScPV1 impairs vegetative growth while enhancing virulence in its fungal host. This finding represents the first instance of a mycovirus responsible for hypervirulence on a phytopathogenic fungus through virion transfection, as well as the first case of a partitivirus conferring hypervirulence while reducing vegetative growth in a phytopathogenic fungus. We anticipate that these findings will significantly advance our understanding of the complex interactions between mycoviruses and their host fungi.

EDITORIAL article Front. Fungal Biol., 12 April 2024Sec. Fungal Pathogenesis Volume 5 - 2024 | https://doi.org/10.3389/ffunb.2024.1404961

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.

Mycoviruses are viruses that infect fungi and are widespread across all major fungal taxa, exhibiting great biological diversity. Since their discovery in the 1960s, researchers have observed a myriad of fungal phenotypes altered due to mycoviral infection. In this review, we examine the nuanced world of mycoviruses in the context of the medically and agriculturally important fungal genus, Aspergillus. The advent of RNA sequencing has revealed a previous underestimate of viral prevalence in fungi, in particular linear single-stranded RNA viruses, and here we outline the diverse viral families known to date that contain mycoviruses infecting Aspergillus. Furthermore, we describe these novel mycoviruses, highlighting those with peculiar genome structures, such as a split RNA dependent RNA polymerase gene. Next, we delineate notable mycovirus-mediated phenotypes in Aspergillus, in particular reporting on observations of mycoviruses that affect their fungal host’s virulence and explore how this may relate to virus-mediated decreased stress tolerance. Furthermore, mycovirus effects on microbial competition and antifungal resistance are discussed. The factors that influence the manifestation of these phenotypes, such as temperature, fungal life stage, and infection with multiple viruses, among others, are also evaluated. In addition, we attempt to elucidate the molecular mechanisms that underpin these phenotypes, examining how mycoviruses can be targets, triggers, and even suppressors of RNA silencing and how this can affect fungal gene expression and phenotypes. Finally, we highlight the potential therapeutic applications of mycoviruses and how, in an approach analogous to bacteriophage therapy, their ability to produce hypovirulence in Aspergillus might be used to attenuate invasive aspergillosis infections in humans.

Circular single-stranded DNA (ssDNA) viruses have been rarely found in fungi, and the evolutionary and ecological relationships among ssDNA viruses infecting fungi and other organisms remain unclear. In this study, a novel circular ssDNA virus, tentatively named Diaporthe sojae circular DNA virus 1 (DsCDV1), was identified in the phytopathogenic fungus Diaporthe sojae isolated from pear trees. DsCDV1 has a monopartite genome (3185 nt in size) encapsidated in isometric virions (21-26 nm in diameter). The genome comprises seven putative open reading frames encoding a discrete replicase (Rep) split by an intergenic region, a putative capsid protein (CP), several proteins of unknown function (P1-P4), and a long intergenic region. Notably, the two split parts of DsCDV1 Rep share high identities with the Reps of Geminiviridae and Genomoviridae, respectively, indicating an evolutionary linkage with both families. Phylogenetic analysis based on Rep or CP sequences placed DsCDV1 in a unique cluster, supporting the establishment of a new family, tentatively named Gegemycoviridae, intermediate to both families. DsCDV1 significantly attenuates fungal growth and nearly erases fungal virulence when transfected into the host fungus. Remarkably, DsCDV1 can systematically infect tobacco and pear seedlings, providing broad-spectrum resistance to fungal diseases. Subcellular localization analysis revealed that DsCDV1 P3 is systematically localized in the plasmodesmata, while its expression in trans-complementation experiments could restore systematic infection of a movement-deficient plant virus, suggesting that P3 is a movement protein. DsCDV1 exhibits unique molecular and biological traits not observed in other ssDNA viruses, serving as a link between fungal and plant ssDNA viruses and presenting an evolutionary connection between ssDNA viruses and fungi. These findings contribute to expanding our understanding of ssDNA virus diversity and evolution, offering potential biocontrol applications for managing crucial plant diseases.

Background: The placenta exerts a crucial role in fetus growth and development during gestation, protecting the fetus from maternal drugs and chemical exposure. However, diverse drugs and chemicals (xenobiotics) can penetrate the maternal placental barrier, leading to deleterious, adverse effects concerning fetus health. Moreover, placental enzymes can metabolize drugs and chemicals into more toxic compounds for the fetus. Thus, evaluating the molecular mechanisms through which drugs and chemicals transfer and undergo metabolism across the placental barrier is of vital importance. In this aspect, this comprehensive literature review aims to provide a holistic approach by critically summarizing and scrutinizing the potential molecular processes and mechanisms governing drugs and chemical transfer and metabolism across the placental barrier, which may lead to fetotoxicity effects, as well as analyzing the currently available experimental methodologies used to assess xenobiotics placental transfer and metabolism. Methods: A comprehensive and in-depth literature review was conducted in the most accurate scientific databases such as PubMed, Scopus, and Web of Science by using relevant and effective keywords related to xenobiotic placental transfer and metabolism, retrieving 8830 published articles until 5 February 2024. After applying several strict exclusion and inclusion criteria, a final number of 148 relevant published articles were included. Results: During pregnancy, several drugs and chemicals can be transferred from the mother to the fetus across the placental barrier by either passive diffusion or through placental transporters, resulting in fetus exposure and potential fetotoxicity effects. Some drugs and chemicals also appear to be metabolized across the placental barrier, leading to more toxic products for both the mother and the fetus. At present, there is increasing research development of diverse experimental methodologies to determine the potential molecular processes and mechanisms of drug and chemical placental transfer and metabolism. All the currently available methodologies have specific strengths and limitations, highlighting the strong demand to utilize an efficient combination of them to obtain reliable evidence concerning drug and chemical transfer and metabolism across the placental barrier. To derive the most consistent and safe evidence, in vitro studies, ex vivo perfusion methods, and in vivo animal and human studies can be applied together with the final aim to minimize potential fetotoxicity effects. Conclusions: Research is being increasingly carried out to obtain an accurate and safe evaluation of drug and chemical transport and metabolism across the placental barrier, applying a combination of advanced techniques to avoid potential fetotoxic effects. The improvement of the currently available techniques and the development of novel experimental protocols and methodologies are of major importance to protect both the mother and the fetus from xenobiotic exposure, as well as to minimize potential fetotoxicity effects.

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.

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.

Paeciliomyces variotii is a thermo-tolerant, ubiquitous fungus commonly found in food products, indoor environments, soil and clinical samples. It is a well-known biocontrol agent used against phytopathogenic fungi and its metabolites have many industrial applications. Rare reports of P. variotii-related human infections have been found in the medical literature. In this study, we report for the first time the infection of P. variotii isolated from a soil sample collected in a rice field with a double-stranded RNA virus, Paeciliomyces variotii partitivirus 1 (PvPV-1) in the family Partitiviridae. P. variotii harboured icosahedral virus particles 30 nm in diameter with two dsRNA segments 1758 and 1356 bp long. Both dsRNA1 and dsRNA2 have a single open reading frame encoding proteins of 63 and 40 kDa, respectively. These proteins have significant similarity to the RNA-dependent RNA polymerase and capsid protein encoded by the genomic segments of several viruses from the family Partitiviridae. Phylogenetic analysis revealed that PvPV-1 belongs to the family Partitiviridae but in an unclassified group/genus, tentatively nominated Zetapartitivirus. PvPV-1 was found to increase the growth rate of the host fungus, as indicated by time course experiments performed on a range of different media for virus-infected and virus-free isogenic lines. Further, dual-culture assays performed for both isogenic lines confirmed the antagonistic potential of P. variotii against other phytopathogenic fungi. The findings of this study assist us in understanding P. variotii as a potential biocontrol agent, together with plant–fungus–virus interactions.