Extracellular transmission of a DNA mycovirus and its use as a natural fungicide

Complete genome analysis of a novel hypovirus in the phytopathogenic fungus Monilinia fructicola

Monilinia fructicola is one of the most devastating fungal diseases of rosaceous fruit crops, both in the field and postharvest, causing significant yield losses. Here, we report the discovery of a novel positive single-stranded RNA virus, Monilinia fructicola hypovirus 3 (MfHV3), in a strain (hf-1) of the phytopathogenic fungus Monilinia fructicola. The complete genome of MfHV3 is 9259 nucleotides (nt) in length and contains a single large open reading frame (ORF) from nt position 462 to 8411. This ORF encodes a polyprotein with three conserved domains, namely UDP-glycosyltransferase, RNA-dependent RNA polymerase (RdRp), and DEAD-like helicase. The MfHV3 polyprotein shares the highest similarity with Colletotrichum camelliae hypovirus 1. Phylogenetic analysis indicated that MfHV3 clustered with members of the genus Betahypovirus within the family Hypoviridae. Taken together, the results of genomic organization comparisons, amino acid sequence alignments, and phylogenetic analysis convincingly show that MfHV3 is a new member of the genus Betahypovirus, family Hypoviridae.

Transmission of mycoviruses: new possibilities

Mycoviruses are viruses that infect fungi. In recent years, an increasing number of mycoviruses have been reported in a wide array of fungi. With the growing interest of scientists and society in reducing the use of agrochemicals, the debate about mycoviruses as an effective next-generation biocontrol has regained momentum. Mycoviruses can have profound effects on the host phenotype, although most viruses have neutral or no effect. We speculate that understanding multiple transmission modes of mycoviruses is central to unraveling the viral ecology and their function in regulating fungal populations. Unlike plant virus transmission via vegetative plant parts, seeds, pollen, or vectors, a widely held view is that mycoviruses are transmitted via vertical routes and only under special circumstances horizontally via hyphal contact depending on the vegetative compatibility groups (i.e., the ability of different fungal strains to undergo hyphal fusion). However, this view has been challenged over the past decades, as new possible transmission routes of mycoviruses are beginning to unravel. In this perspective, we discuss emerging studies with evidence suggesting that such novel routes of mycovirus transmission exist and are pertinent to understanding the full picture of mycovirus ecology and evolution.

Identification of mungbean yellow mosaic India virus and susceptibility-related metabolites in the apoplast of mung bean leaves

KEY MESSAGE

The investigation of MYMIV-infected mung bean leaf apoplast revealed viral genome presence, increased EVs secretion, and altered stress-related metabolite composition, providing comprehensive insights into plant-virus interactions. The apoplast, an extracellular space around plant cells, plays a vital role in plant-microbe interactions, influencing signaling, defense, and nutrient transport. While the involvement of apoplast and extracellular vesicles (EVs) in RNA virus infection is documented, the role of the apoplast in plant DNA viruses remains unclear. This study explores the apoplast's role in mungbean yellow mosaic India virus (MYMIV) infection. Our findings demonstrate the presence of MYMIV genomic components in apoplastic fluid, suggesting potential begomovirus cell-to-cell movement via the apoplast. Moreover, MYMIV infection induces increased EVs secretion into the apoplast. NMR-based metabolomics reveals altered metabolic profiles in both apoplast and symplast in response to MYMIV infection, highlighting key metabolites associated with stress and defense mechanisms. The data show an elevation of α- and β-glucose in both apoplast and symplast, suggesting a shift in glucose utilization. Interestingly, this increase in glucose does not contribute to the synthesis of phenolic compounds, potentially influencing the susceptibility of mung bean to MYMIV. Fructose levels increase in the symplast, while apoplastic sucrose levels rise significantly. Symplastic aspartate levels increase, while proline exhibits elevated concentration in the apoplast and reduced concentration in the cytosol, suggesting a role in triggering a hypersensitive response. These findings underscore the critical role of the apoplast in begomovirus infection, providing insights for targeted viral disease management strategies.

Beneficial effects of Bacillus mojavensis strain MTC-8 on plant growth, immunity and disease resistance against Magnaporthe oryzae

Rice blast, a prevalent and highly destructive rice disease that significantly impacts rice yield, is caused by the rice blast fungus. In the present study, a strain named MTC-8, identified as Bacillus mojavensis, was demonstrated has strong antagonistic activity against the rice blast fungus, Rhizoctonia solani, Ustilaginoidea virens, and Bipolaria maydis. The potential biocontrol agents were identified using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis and chromatography. Further investigations elucidated the inhibitory mechanism of the isolated compound and demonstrated its ability to suppress spore germination, alter hyphal morphology, disrupt cell membrane integrity, and induce defense-related gene expression in rice. MTC-8 promoted plant growth and may lead to the development of a biocontrol agent that meets agricultural standards. Overall, the Bacillus mojavensis MTC-8 strain exerted beneficial effects on plant growth, immunity and disease resistance against rice blast fungus. In this study, we isolated and purified a bioactive substance from fermentation broth, and the results provide a foundation for the development and application of biopesticides. Elucidation of the inhibitory mechanism against rice blast fungus provides theoretical support for the identification of molecular targets. The successful development of a biocontrol agent lays the groundwork for its practical application in agriculture.

Plants interfere with non-self recognition of a phytopathogenic fungus via proline accumulation to facilitate mycovirus transmission

Non-self recognition is a fundamental aspect of life, serving as a crucial mechanism for mitigating proliferation of molecular parasites within fungal populations. However, studies investigating the potential interference of plants with fungal non-self recognition mechanisms are limited. Here, we demonstrate a pronounced increase in the efficiency of horizontal mycovirus transmission between vegetatively incompatible Sclerotinia sclerotiorum strains in planta as compared to in vitro. This increased efficiency is associated with elevated proline concentration in plants following S. sclerotiorum infection. This surge in proline levels attenuates the non-self recognition reaction among fungi by inhibition of cell death, thereby facilitating mycovirus transmission. Furthermore, our field experiments reveal that the combined deployment of hypovirulent S. sclerotiorum strains harboring hypovirulence-associated mycoviruses (HAVs) together with exogenous proline confers substantial protection to oilseed rape plants against virulent S. sclerotiorum. This unprecedented discovery illuminates a novel pathway by which plants can counteract S. sclerotiorum infection, leveraging the weakening of fungal non-self recognition and promotion of HAVs spread. These promising insights provide an avenue to explore for developing innovative biological control strategies aimed at mitigating fungal diseases in plants by enhancing the efficacy of horizontal HAV transmission.

A circular single-stranded DNA mycovirus infects plants and confers broad-spectrum fungal resistance

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.

Discovery of novel RNA viruses through analysis of fungi-associated next-generation sequencing data

BACKGROUND

Like all other species, fungi are susceptible to infection by viruses. The diversity of fungal viruses has been rapidly expanding in recent years due to the availability of advanced sequencing technologies. However, compared to other virome studies, the research on fungi-associated viruses remains limited.

RESULTS

In this study, we downloaded and analyzed over 200 public datasets from approximately 40 different Bioprojects to explore potential fungal-associated viral dark matter. A total of 12 novel viral sequences were identified, all of which are RNA viruses, with lengths ranging from 1,769 to 9,516 nucleotides. The amino acid sequence identity of all these viruses with any known virus is below 70%. Through phylogenetic analysis, these RNA viruses were classified into different orders or families, such as Mitoviridae, Benyviridae, Botourmiaviridae, Deltaflexiviridae, Mymonaviridae, Bunyavirales, and Partitiviridae. It is possible that these sequences represent new taxa at the level of family, genus, or species. Furthermore, a co-evolution analysis indicated that the evolutionary history of these viruses within their groups is largely driven by cross-species transmission events.

CONCLUSIONS

These findings are of significant importance for understanding the diversity, evolution, and relationships between genome structure and function of fungal viruses. However, further investigation is needed to study their interactions.

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.

Molecular and biological characterization of a novel partitivirus from Talaromyces pinophilus

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.

Fusarium sacchari hypovirus 1, a Member of Hypoviridae with Virulence Attenuation Capacity in Phytopathogenic Fusarium Species

In a survey of mycoviruses in Fusarium species that cause sugarcane Pokkah boeng disease, twelve Fusarium strains from three Fusarium species (F. sacchari, F. andiyazi, and F. solani) were found to contain Fusarium sacchari hypovirus 1 (FsHV1), which we reported previously. The genomes of these variants range from 13,966 to 13,983 nucleotides, with 98.6% to 99.9% nucleotide sequence identity and 98.70% to 99.9% protein sequence similarity. Phylogenetic analysis placed these FsHV1 variants within the Alphahypovirus cluster of Hypoviridae. Intriguingly, no clear correlation was found between the geographic origin and host specificity of these viral variants. Additionally, six out of the twelve variants displayed segmental deletions of 1.5 to 1.8 kilobases, suggesting the existence of defective viral dsRNA. The presence of defective viral dsRNA led to a two-thirds reduction in the dsRNA of the wild-type viral genome, yet a tenfold increase in the total viral dsRNA content. To standardize virulence across natural strains, all FsHV1 strains were transferred into a single, virus-free Fusarium recipient strain, FZ06-VF, via mycelial fusion. Strains of Fusarium carrying FsHV1 exhibited suppressed pigment synthesis, diminished microspore production, and a marked decrease in virulence. Inoculation tests revealed varying capacities among different FsHV1 variants to modulate fungal virulence, with the strain harboring the FsHV1-FSA1 showing the lowest virulence, with a disease severity index (DSI) of 3.33, and the FsHV1-FS1 the highest (DSI = 17.66). The identification of highly virulent FsHV1 variants holds promise for the development of biocontrol agents for Pokkah boeng management.

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.

An endogenous DNA virus in an amphibian-killing fungus associated with pathogen genotype and virulence

The global panzootic lineage (GPL) of the pathogenic fungus Batrachochytrium dendrobatidis (Bd) has caused severe amphibian population declines, yet the drivers underlying the high frequency of GPL in regions of amphibian decline are unclear. Using publicly available Bd genome sequences, we identified multiple non-GPL Bd isolates that contain a circular Rep-encoding single-stranded (CRESS)-like DNA virus, which we named Bd DNA virus 1 (BdDV-1). We further sequenced and constructed genome assemblies with long read sequences to find that the virus is integrated into the nuclear genome in some strains. Attempts to cure virus-positive isolates were unsuccessful; however, phenotypic differences between naturally virus-positive and virus-negative Bd isolates suggested that BdDV-1 decreases the growth of its host in vitro but increases the virulence of its host in vivo. BdDV-1 is the first-described CRESS DNA mycovirus of zoosporic true fungi, with a distribution inversely associated with the emergence of the panzootic lineage.

Complete genome sequence of a novel dsRNA virus from the phytopathogenic fungus Fusarium oxysporum

Fusarium oxysporum is a widespread plant pathogen that causes fusarium wilt and fusarium root rot in many economically significant crops. Here, a novel dsRNA virus tentatively named "Fusarium oxysporum virus 1" (FoV1) was identified in F. oxysporum strain 3S-18. The genome of FoV1 is 2,944 nucleotides (nt) in length and contains two non-overlapping open reading frames (ORF1 and 2). The larger of these, ORF2, encodes an RNA-dependent RNA polymerase (RdRp) of 590 amino acids with a molecular mass of 67.52 kDa. ORF1 encodes a putative nucleocapsid protein consisting of 134 amino acids with a molecular mass of 34.25 kDa. The RdRp domain of FoV1 shares 60.00% to 84.24% sequence identity with non-segmented dsRNA viruses. Phylogenetic analysis further suggested that FoV1 is a new member of the proposed genus "Unirnavirus" accommodating unclassified monopartite dsRNA viruses.

A Wnt10a-Notch signaling axis controls Hertwig's epithelial root sheath cell behaviors during root furcation patterning

Human with bi-allelic WNT10A mutations and epithelial Wnt10a knockout mice present enlarged pulp chamber and apical displacement of the root furcation of multi-rooted teeth, known as taurodontism; thus, indicating the critical role of Wnt10a in tooth root morphogenesis. However, the endogenous mechanism by which epithelial Wnt10a regulates Hertwig's epithelial root sheath (HERS) cellular behaviors and contributes to root furcation patterning remains unclear. In this study, we found that HERS in the presumptive root furcating region failed to elongate at an appropriate horizontal level in K14-Cre;Wnt10afl/fl mice from post-natal day 0.5 (PN0.5) to PN4.5. EdU assays and immunofluorescent staining of cyclin D1 revealed significantly decreased proliferation activity of inner enamel epithelial (IEE) cells of HERS in K14-Cre;Wnt10afl/fl mice at PN2.5 and PN3.5. Immunofluorescent staining of E-Cadherin and acetyl-α-Tubulin demonstrated that the IEE cells of HERS tended to divide perpendicularly to the horizontal plane, which impaired the horizontal extension of HERS in the presumptive root furcating region of K14-Cre;Wnt10afl/fl mice. RNA-seq and immunofluorescence showed that the expressions of Jag1 and Notch2 were downregulated in IEE cells of HERS in K14-Cre;Wnt10afl/fl mice. Furthermore, after activation of Notch signaling in K14-Cre;Wnt10afl/fl molars by Notch2 adenovirus and kidney capsule grafts, the root furcation defect was partially rescued. Taken together, our study demonstrates that an epithelial Wnt10a-Notch signaling axis is crucial for modulating HERS cell proper proliferation and horizontal-oriented division during tooth root furcation morphogenesis.

Characterization of the RNA Mycovirome Associated with Grapevine Fungal Pathogens: Analysis of Mycovirus Distribution and Their Genetic Variability within a Collection of Botryosphaeriaceae Isolates

Botryosphaeriaceae are fungi involved in the decay of various woody species, including the grapevine, leading to significant production losses. This fungal family is largely ubiquitous, and seven species of Botryosphaeriaceae have been identified in French vineyards, with variable levels of aggressiveness, both in vitro and in planta. Mycoviruses can impact the life traits of their fungal hosts, including aggressiveness, and are one of the factors influencing fungal pathogenicity. In this study, the RNA mycovirome of fifteen Botryosphaeriaceae isolates was characterized through the high-throughput sequencing of double-stranded RNA preparations from the respective samples. Eight mycoviruses were detected, including three potential novel species in the Narnaviridae family, as well as in the proposed Mycobunyaviridae and Fusagraviridae families. A large collection of Botryosphaeriaceae isolates was screened using RT-PCR assays specific for 20 Botryosphaeriaceae-infecting mycoviruses. Among the mycoviruses detected, some appeared to be specialists within a single host species, while others infected isolates belonging to multiple Botryosphaeriaceae species. This screening allowed us to conclude that one-third of the Botryosphaeriaceae isolates were infected by at least one mycovirus, and a significant proportion of isolates (43.5%) were found to be coinfected by several viruses, with very complex RNA mycoviromes for some N. parvum isolates.

Exploring the Mycovirus Sclerotinia sclerotiorum Hypovirulence-Associated DNA Virus 1 as a Biocontrol Agent of White Mold Caused by Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a necrotrophic fungal pathogen causing white mold on many important economic crops. Recently, some mycoviruses such as S. sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1) converted S. sclerotiorum into a beneficial symbiont that helps plants manage pathogens and other stresses. To explore the potential use of SsHADV-1 as a biocontrol agent in the United States and to test the efficacy of SsHADV-1-infected United States isolates in managing white mold and other crop diseases, SsHADV-1 was transferred from the Chinese strain DT-8 to United States isolates of S. sclerotiorum. SsHADV-1 is readily transmitted horizontally among United States isolates of S. sclerotiorum and consistently conferred hypovirulence to its host strains. Biopriming of dry bean seeds with hypovirulent S. sclerotiorum strains enhanced resistance to white mold, gray mold, and Rhizoctonia root rot. To investigate the underlying mechanisms, endophytic growth of hypovirulent S. sclerotiorum in dry beans was confirmed using PCR, and the expression of 12 plant defense-related genes were monitored before and after infection. The results indicated that the endophytic growth of SsHADV-1-infected strains in plants stimulated the expression of plant immunity pathway genes that assisted a rapid response from the plant to fungal infection. Finally, application of the seed biopriming technology with SsHADV-1-infected hypervirulent strain has promise for the biological control of several diseases of wheat, pea, and sunflower.

Identification of Mycoviruses in the Pathogens of Fragrant Pear Valsa Canker from Xinjiang in China

As a common disease, canker seriously affects the yield and quality of fragrant pear due to the lack of effective control measures. Some fungi have been reported to harbor rich reservoirs of viral resources, and some mycoviruses can be used as biocontrol agents against plant diseases. In this study, 199 isolates were obtained from diseased branches of fragrant pear in the main production areas of Xinjiang. Among them, 134 belonged to Valsa spp., identified using morphological and molecular biological techniques, in which V. mali was the dominant species. The mycoviruses in Valsa spp. were further identified using metatranscriptomic sequencing and RT-PCR. The results revealed that a total of seven mycoviruses were identified, belonging to Botourmiaviridae, Endornaviridae, Fusariviridae, Hypoviridae, Mitoviridae, and Narnaviridae, among which Phomopsis longicolla hypovirus (PlHV) was dominant in all the sample collection regions. The Cryphonectria hypovirus 3-XJ1 (CHV3-XJ1), Botourmiaviridae sp.-XJ1 (BVsp-XJ1), and Fusariviridae sp.-XJ1 (Fvsp-XJ1) were new mycoviruses discovered within the Valsa spp. More importantly, compared with those in the virus-free Valsa spp. strain, the growth rate and virulence of the VN-5 strain co-infected with PlHV and CHV3-XJ1 were reduced by 59% and 75%, respectively, and the growth rate and virulence of the VN-34 strain infected with PlHV were reduced by 42% and 55%, respectively. On the other hand, the horizontal transmission efficiency of PlHV decreased when PlHV was co-infected with CHV3-XJ1, indicating that PlHV and CHV3-XJ1 were antagonistic. In summary, the mycoviruses in Valsa spp. were identified in Xinjiang for the first time, and three of them were newly discovered mycoviruses, with two strains yielding good results. These results will offer potential biocontrol resources for managing pear canker disease and provide a theoretical basis for the control of fruit tree Valsa canker disease.

The Effects of Mycovirus BmPV36 on the Cell Structure and Transcription of Bipolaris maydis

Bipolaris maydis partitivirus 36 (BmPV36) is a mycovirus that can significantly reduce the virulence of the host Bipolaris maydis, but its hypovirulence mechanism is not clear. To investigate the response of B. maydis to BmPV36, the effects of BmPV36 on host cell structure and gene expression were studied via transmission electron microscopy and transcriptome sequencing using BmPV36-carrying and virus-free mycelium on the second and fifth culture. The results of transmission electron microscopy showed that the cell wall microfibrils of B. maydis were shortened, the cell membrane was broken, and membrane-bound vesicles and vacuoles appeared in the cells after carrying BmPV36. Transcriptome sequencing results showed that after carrying BmPV36, B. maydis membrane-related genes were significantly up-regulated, but membrane transport-related genes were significantly down-regulated. Genes related to carbohydrate macromolecule polysaccharide metabolic and catabolic processes were significantly down-regulated, as were genes related to the synthesis of toxins and cell wall degrading enzymes. Therefore, we speculated that BmPV36 reduces the virulence of B. maydis by destroying the host's cell structure, inhibiting the synthesis of toxins and cell wall degrading enzymes, and reducing cell metabolism. Gaining insights into the hypovirulence mechanism of mycoviruses will provide environmentally friendly strategies for the control of fungal diseases.

The Interaction between Hypovirulence-Associated Chrysoviruses and Their Host Fusarium Species

Chrysoviruses are isometric virus particles (35-50 nm in diameter) with a genome composed of double-stranded RNAs (dsRNA). These viruses belonged to the Chrysoviridae family, named after the first member isolated from Penicillium chrysogenum. Phylogenetic classification has divided the chrysoviruses into Alphachrysovirus and Betachrysovirus genera. Currently, these chrysoviruses have been found to infect many fungi, including Fusarium species, and cause changes in the phenotype and decline in the pathogenicity of the host. Thus, it is a microbial resource with great biocontrol potential against Fusarium species, causing destructive plant diseases and substantial economic losses. This review provides a comprehensive overview of three chrysovirus isolates (Fusarium graminearum virus 2 (FgV2), Fusarium graminearum virus-ch9 (FgV-ch9), and Fusarium oxysporum f. sp. dianthi mycovirus 1 (FodV1)) reported to decline the pathogenicity of Fusarium hosts. It also summarizes the recent studies on host response regulation, host RNA interference, and chrysovirus transmission. The information provided in the review will be a reference for analyzing the interaction of Fusarium species with chrysovirus and proposing opportunities for research on the biocontrol of Fusarium diseases. Finally, we present reasons for conducting further studies on exploring the interaction between chrysoviruses and Fusarium and improving the accumulation and transmission efficiency of these chrysoviruses.

Identification of Mycoviruses by dsRNA Extraction

Mycoviruses exist in all major groups of fungi. With the continuous development of science and technology, the methods of studying viruses are constantly updated, and progressively mycoviruses have been discovered where most of these viruses are RNA viruses. Therefore, double-stranded RNA has traditionally been used as the hallmark of RNA mycovirus detection. This report describes in detail the method of mycovirus identification using extraction of dsRNA. Besides, extraction of viral dsRNA, and the assembly methods of viral genome and identification of virus type are presented.

The Wheat Endophyte Epicoccum layuense J4-3 Inhibits Fusarium graminearum and Enhances Plant Growth

Fungal endophytes are well-known for their ability to promote plant growth and hinder fungal diseases, including Fusarium head blight (FHB) caused by Fusarium graminearum. This study aimed to characterize the biocontrol efficacy of strain J4-3 isolated from the stem of symptomless wheat collected from Heilongjiang Province, China. It was identified as Epicoccum layuense using morphological characteristics and phylogenetic analysis of the rDNA internal transcribed spacer (ITS) and beta-tubulin (TUB). In a dual culture assay, strain J4-3 significantly inhibited the mycelial growth of F. graminearum strain PH-1 and other fungal pathogens. In addition, wheat coleoptile tests showed that lesion symptoms caused by F. graminearum were significantly reduced in wheat seedlings treated with hyphal fragment suspensions of strain J4-3 compared to the controls. Under field conditions, applying spore suspensions and culture filtrates of strain J4-3 with conidial suspensions of F. graminearum on wheat spikes resulted in the significant biocontrol efficacy of FHB. In addition, wheat seedlings previously treated with spore suspensions of strain J4-3 before sowing successfully resulted in FHB reduction after the application of conidial suspensions of F. graminearum at anthesis. More importantly, wheat seedlings treated with hyphal fragments and spore suspensions of strain J4-3 showed significant increases in wheat growth compared to the controls under greenhouse and field conditions. Overall, these findings suggest that E. layuense J4-3 could be a promising biocontrol agent (BCA) against F. graminearum, causing FHB and a growth-promoting fungus in wheat.

Viruses of plant-pathogenic fungi: a promising biocontrol strategy for Sclerotinia sclerotiorum

Plant pathogenic fungi pose a significant and ongoing threat to agriculture and food security, causing economic losses and significantly reducing crop yields. Effectively managing these fungal diseases is crucial for sustaining agricultural productivity, and in this context, mycoviruses have emerged as a promising biocontrol option. These viruses alter the physiology of their fungal hosts and their interactions with the host plants. This review encompasses the extensive diversity of reported mycoviruses, including their taxonomic classification and range of fungal hosts. We highlight representative examples of mycoviruses that affect economically significant plant-pathogenic fungi and their distinctive characteristics, with a particular emphasis on mycoviruses impacting Sclerotinia sclerotiorum. These mycoviruses exhibit significant potential for biocontrol, supported by their specificity, efficacy, and environmental safety. This positions mycoviruses as valuable tools in crop protection against diseases caused by this pathogen, maintaining their study and application as promising research areas in agricultural biotechnology. The remarkable diversity of mycoviruses, coupled with their ability to infect a broad range of plant-pathogenic fungi, inspires optimism, and suggests that these viruses have the potential to serve as an effective management strategy against major fungi-causing plant diseases worldwide.

Targeting wheat fusarium head blight with mycovirus-mediated VIGS

Fusarium head blight (FHB) caused by Fusarium graminearum occurs in wheat (Triticum aestivum) and threatens food production worldwide. Wheat lacks broad, durable FHB resistance. However, Zhang et al. developed a mycovirus-based virus-induced gene-silencing system in F. graminearum, providing efficient biocontrol of this devastating fungal disease.

Novel plant-associated genomoviruses from the Brazilian Cerrado biome

The discovery rate of new plant viruses has increased due to studies involving high-throughput sequencing (HTS), particularly for single-stranded DNA viruses of the family Genomoviridae. We carried out an HTS-based survey of genomoviruses in a wide range of native and exotic trees grown in the Brazilian Cerrado biome, and the complete genome sequences of two novel members of the family Genomoviridae from two distinct genera were determined. Specific primers were designed to detect these genomoviruses in individual samples. A new gemykolovirus (Tecoma stans associated gemykolovirus) was detected in Tecoma stans, and a new gemykibivirus (Ouratea duparquetiana associated gemykibivirus) was detected in Ouratea duparquetiana. A gemykrogvirus related to Gila monster associated gemykrogvirus (80% pairwise identity) was also detected in foliar samples of Trembleya parviflora. Our pilot study paves the way for a better characterization of this diverse collection of genomoviruses as well as their interactions with the associated tree species.

Hypovirulence-associated mycovirus epidemics cause pathogenicity degeneration of Beauveria bassiana in the field

BACKGROUND

The entomogenous fungus Beauveria bassiana is used as a biological insecticide worldwide, wild B. bassiana strains with high pathogenicity in the field play an important role in controlling insect pests via not only screening of highly virulent strains but also natural infection, but the pathogenicity degeneration of wild strains severely affected aforementioned effects. Previous studies have showed that multiple factors contributed to this phenomenon. It has been extensively proved that the mycovirus infection caused hypovirulence of phytopathogenic fungi, which has been used for plant disease biocontrol. However, it remains unknown whether the mycovirus epidemics is a key factor causing hypovirulence of B. bassiana naturally in the field.

METHODS

Wild strains of B. bassiana were collected from different geographic locations in Jilin Province, China, to clarify the epidemic and diversity of the mycoviruses. A mycovirus Beauveria bassiana chrysovirus 2 (BbCV2) we have previously identified was employed to clarify its impact on the pathogenicity of host fungi B. bassiana against the larvae of insect pest Ostrinia furnacalis. The serological analysis was conducted by preparing polyclonal antibody against a BbCV2 coat protein, to determine whether it can dissociate outside the host fungal cells and subsequently infect new hosts. Transcriptome analysis was used to reveal the interactions between viruses and hosts.

RESULTS

We surprisingly found that the mycovirus BbCV2 was prevalent in the field as a core virus in wild B. bassiana strains, without obvious genetic differentiation, this virus possessed efficient and stable horizontal and vertical transmission capabilities. The serological results showed that the virus could not only replicate within but also dissociate outside the host cells, and the purified virions could infect B. bassiana by co-incubation. The virus infection causes B. bassiana hypovirulence. Transcriptome analysis revealed decreased expression of genes related to insect epidermis penetration, hypha growth and toxin metabolism in B. bassiana caused by mycovirus infection.

CONCLUSION

Beauveria bassiana infected by hypovirulence-associated mycovirus can spread the virus to new host strains after infecting insects, and cause the virus epidemics in the field. The findings confirmed that mycovirus infection may be an important factor affecting the pathogenicity degradation of B. bassiana in the field.

Mechanisms of Primed Defense: Plant Immunity Induced by Endophytic Colonization of a Mycovirus-Induced Hypovirulent Fungal Pathogen

How mycovirus-induced hypovirulence in fungi activates plant defense is still poorly understood. The changes in plant fitness and gene expression caused by the inoculation of the fungus Sclerotinia sclerotiorum harboring and made hypovirulent by the mycovirus soybean leaf-associated gemygorvirus-1 (SlaGemV-1) of the species Gemycircularvirus soybe1 were examined in this study. As the hypovirulent fungus (DK3V) colonized soybean Glycine max, plant transcriptomic analysis indicated changes in defense responses and photosynthetic activity, supported by an upregulation of individual genes and overrepresentation of photosystem gene ontology groups. The upregulated genes include genes relating to both pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity as well as various genes relating to the induction of systemic acquired resistance and the biosynthesis of jasmonic acid. Plants colonized with DK3V showed a resistant phenotype to virulent S. sclerotiorum infection. Plant height and leaf area were also determined to be larger in plants grown with the virus-infected fungus. Here, we hypothesize that inoculation of soybean with DK3V can result in the triggering of a wide range of defense mechanisms to prime against later infection. The knowledge gained from this study about plant transcriptomics and phenotype will help prime plant immunity with mycovirus-infected hypovirulent fungal strains more effectively. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A Mycovirus VIGS Vector Confers Hypovirulence to a Plant Pathogenic Fungus to Control Wheat FHB

Mycovirus-mediated hypovirulence has the potential to control fungal diseases. However, the availability of hypovirulence-conferring mycoviruses for plant fungal disease control is limited as most fungal viruses are asymptomatic. In this study, the virus-induced gene silencing (VIGS) vector p26-D4 of Fusarium graminearum gemytripvirus 1 (FgGMTV1), a tripartite circular single-stranded DNA mycovirus, is successfully constructed to convert the causal fungus of cereal Fusarium head blight (FHB) into a hypovirulent strain. p26-D4, with an insert of a 75-150 bp fragment of the target reporter transgene transcript in both sense and antisense orientations, efficiently triggered gene silencing in Fusarium graminearum. Notably, the two hypovirulent strains, p26-D4-Tri101, and p26-D4-FgPP1, obtained by silencing the virulence-related genes Tri101 and FgPP1 with p26-D4, can be used as biocontrol agents to protect wheat from a fungal disease FHB and mycotoxin contamination at the field level. This study not only describes the first mycovirus-derived VIGS system but also proves that the VIGS vector can be used to establish multiple hypovirulent strains to control pathogenic fungi.

The intriguing phenomenon of cross-kingdom infections of plant and insect viruses to fungi: Can other animal viruses also cross-infect fungi?

Fungi are highly widespread and commonly colonize multicellular organisms that live in natural environments. Notably, studies on viruses infecting plant-associated fungi have revealed the interesting phenomenon of the cross-kingdom transmission of viruses and viroids from plants to fungi. This implies that fungi, in addition to absorbing water, nutrients, and other molecules from the host, can acquire intracellular parasites that reside in the host. These findings further suggest that fungi can serve as suitable alternative hosts for certain plant viruses and viroids. Given the frequent coinfection of fungi and viruses in humans/animals, the question of whether fungi can also acquire animal viruses and serve as their hosts is very intriguing. In fact, the transmission of viruses from insects to fungi has been observed. Furthermore, the common release of animal viruses into the extracellular space (viral shedding) could potentially facilitate their acquisition by fungi. Investigations of the cross-infection of animal viruses in fungi may provide new insights into the epidemiology of viral diseases in humans and animals.

BdCV1-Encoded P3 Silencing Suppressor Identification and Its Roles in Botryosphaeria dothidea, Causing Pear Ring Rot Disease

Pear ring rot disease is an important branch disease, caused by Botryosphaeria dothidea. With the discovery of fungal viruses, the use of their attenuated properties for biological control provides a new strategy for the biological control of fungal disease. RNA silencing is a major antiviral defense mechanism in plants, insects, and fungi. Viruses encode and utilize RNA silencing suppressors to suppress host defenses. Previous studies revealed that Botryosphaeria dothidea chrysovirus 1 (BdCV1) exhibited weak pathogenicity and could activate host gene silencing by infecting B. dothidea. The aim of our study was to investigate whether BdCV1 can encode a silencing suppressor and what effect it has on the host. In this study, the capability of silencing inhibitory activity of four BdCV1-encoded proteins was analyzed, and the P3 protein was identified as a BdCV1 RNA silencing suppressor in the exotic host Nicotiana benthamiana line 16c. In addition, we demonstrated that P3 could inhibit local silencing, block systemic RNA silencing, and induce the necrosis reaction of tobacco leaves. Furthermore, overexpression of P3 could slow down the growth rate and reduce the pathogenicity of B. dothidea, and to some extent affect the expression level of RNA silencing components and virus-derived siRNAs (vsiRNAs). Combined with transcriptomic analysis, P3 had an effect on the gene expression and biological process of B. dothidea. The obtained results provide new theoretical information for further study of interaction between BdCV1 P3 as a potential silencing suppressor and B. dothidea.

Cross-Kingdom Interactions Between Plant and Fungal Viruses

The large genetic and structural divergences between plants and fungi may hinder the transmission of viruses between these two kingdoms to some extent. However, recent accumulating evidence from virus phylogenetic analyses and the discovery of naturally occurring virus cross-infection suggest the occurrence of past and current transmissions of viruses between plants and plant-associated fungi. Moreover, artificial virus inoculation experiments showed that diverse plant viruses can multiply in fungi and vice versa. Thus, virus cross-infection between plants and fungi may play an important role in the spread, emergence, and evolution of both plant and fungal viruses and facilitate the interaction between them. In this review, we summarize current knowledge related to cross-kingdom virus infection in plants and fungi and further discuss the relevance of this new virological topic in the context of understanding virus spread and transmission in nature as well as developing control strategies for crop plant diseases.

Characterization of a novel hypovirus isolated from the phytopathogenic fungus Colletotrichum camelliae

Some members of genus Colletotrichum are important plant pathogens. Here, we report a novel positive single-stranded RNA virus, Colletotrichum camelliae hypovirus 1 (CcHV1), from strain GXNN11-2 of Colletotrichum camelliae. The complete genome of CcHV1 is 9907 nucleotides (nt) in length and contains a single large open reading frame (ORF) from nt 352 to 9006. This ORF encodes a polyprotein with four conserved domains, namely UDP-glycosyltransferase, RNA-dependent RNA polymerase (RdRp), peptidase, and DEAD-like helicase. The CcHV1 polyprotein shares the highest similarity with Fusarium concentricum hypovirus 1. Phylogenetic analysis indicated that CcHV1 clustered with members of the genus Betahypovirus within the family Hypoviridae. This is the first report of a hypovirus in a member of the genus Colletotrichum.

Complete genome sequence of a novel double-stranded RNA virus infecting the phytopathogenic fungus Rhizopus stolonifer

In this study, we report the complete genome sequence of a novel toti-like virus, tentatively named "Rhizopus stolonifer double-stranded RNA virus 1" (RsDSV1), identified from a phytopathogenic fungal agent of apple fruit rot disease, Rhizopus stolonifer strain A2-1. RsDSV1 has a double-stranded RNA genome. The complete RsDSV1 genome is 5178 nucleotides (nt) in length and contains two open reading frames (ORFs) encoding a putative coat protein (CP) and an RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis based on RdRp and CP amino acid sequences revealed that RsDSV1 is closely related to unclassified members of the family Totiviridae. In stress-inducing Vogel's minimal and sodium dodecyl sulfate-containing media, hyphal growth of A2-1 was suppressed, but the accumulation of RsDSV1 RNA increased, indicating that stresses promote RsDSV1 replication. To our knowledge, this is the first report of a mycovirus found in R. stolonifer.

Experimental verification of strain-dependent relationship between mycovirus and its fungal host

Mycoviruses are viruses that infect fungi. Unlike mammalian infectious viruses, their life cycle does not generally have an extracellular stage, and a symbiosis-like relationship is maintained between virus and host fungi. Recently, mycoviruses have been reported to show effects on host fungi, altering biological properties such as growth rate, virulence, drug resistance, and metabolite production. In this study, we systematically elucidated the effects of viruses on host cells by comparing host phenotypes and transcriptomic responses in multiple sets of virus-infected and -eliminated Aspergillus flavus strains. The comparative study showed that mycoviruses affect several cellular activities at the molecular level in a virus- and host strain-dependent manner. The virus-swapping experiment revealed that difference with only three bases in the virus genome led to different host fungal response at the transcriptional level. Our results highlighted highly specific relationship between viruses and their host fungi.

The good, the bad and the cryptic: The multifaceted roles of mycoviruses and their potential applications for a sustainable agriculture

Mycoviruses are natural inhabitants of fungi and have been identified in almost all fungal taxonomic groups. Mycoviruses that infect phytopathogenic fungi are now becoming a hot research area due to their potential for the biocontrol of important plant pathogens. But, before considering a mycovirus for biocontrol, we should be fully aware of the effects it induces in a fungal host and its interactions with other viruses, fungal strains and even the host plants. Mycoviral infections are generally associated with different effects, ranging from hypovirulence to hypervirulence, but they can often be cryptic (latent infections). The cryptic lifestyle has been associated to many mycoviruses, but thanks to growing knowledge we are now aware that it is often associated to axenic conditions while the real effects can be observed only in nature. Other mycoviruses either promote (hypervirulence) or (hypovirulence) fungal pathogenicity by a strong impact on the fungal physiology or by blocking the production of toxins or effectors. Finally, indirect effects of mycoviral infections can also be provided to the plant that hosts the fungal isolate, highlighting not only their potential as direct biocontrol agents but also as priming agents for plant resilience to biotic and abiotic stresses. This review provides a broad overview of mycoviral interactions both with their hosts and with other mycoviruses, highlighting the most interesting examples. In contrast to what has been observed to date, we believe that the collective availability of these data will not only improve our understanding of mycoviruses, but also increase our confidence in considering them as alternative measures against fungal diseases to improve the sustainable production of food and feed commodities.

Novel viruses of the family Partitiviridae discovered in Saccharomyces cerevisiae

It has been 49 years since the last discovery of a new virus family in the model yeast Saccharomyces cerevisiae. A large-scale screen to determine the diversity of double-stranded RNA (dsRNA) viruses in S. cerevisiae has identified multiple novel viruses from the family Partitiviridae that have been previously shown to infect plants, fungi, protozoans, and insects. Most S. cerevisiae partitiviruses (ScPVs) are associated with strains of yeasts isolated from coffee and cacao beans. The presence of partitiviruses was confirmed by sequencing the viral dsRNAs and purifying and visualizing isometric, non-enveloped viral particles. ScPVs have a typical bipartite genome encoding an RNA-dependent RNA polymerase (RdRP) and a coat protein (CP). Phylogenetic analysis of ScPVs identified three species of ScPV, which are most closely related to viruses of the genus Cryspovirus from the mammalian pathogenic protozoan Cryptosporidium parvum. Molecular modeling of the ScPV RdRP revealed a conserved tertiary structure and catalytic site organization when compared to the RdRPs of the Picornaviridae. The ScPV CP is the smallest so far identified in the Partitiviridae and has structural homology with the CP of other partitiviruses but likely lacks a protrusion domain that is a conspicuous feature of other partitivirus particles. ScPVs were stably maintained during laboratory growth and were successfully transferred to haploid progeny after sporulation, which provides future opportunities to study partitivirus-host interactions using the powerful genetic tools available for the model organism S. cerevisiae.

A novel partitivirus orchestrates conidiation, stress response, pathogenicity, and secondary metabolism of the entomopathogenic fungus Metarhizium majus

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.

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses

Mycoviruses (viruses of fungi) are ubiquitous throughout the fungal kingdom and are currently classified into 23 viral families and the genus botybirnavirus by the International Committee on the Taxonomy of Viruses (ICTV). The primary focus of mycoviral research has been on mycoviruses that infect plant pathogenic fungi, due to the ability of some to reduce the virulence of their host and thus act as potential biocontrol against these fungi. However, mycoviruses lack extracellular transmission mechanisms and rely on intercellular transmission through the hyphal anastomosis, which impedes successful transmission between different fungal strains. This review provides a comprehensive overview of mycoviruses, including their origins, host range, taxonomic classification into families, effects on their fungal counterparts, and the techniques employed in their discovery. The application of mycoviruses as biocontrol agents of plant pathogenic fungi is also discussed.

Mycoviruses in Fungi: Carcinogenesis of Fungal Agents May Not Always Be Mycotoxin Related

Certain viruses have been found to induce diverse biological pathways to carcinogenesis, evidenced by the presence of viral gene products in some tumors. Despite the fact that many fungal agents contain mycoviruses, until recently, their possible direct effects on human health, including carcinogenesis and leukemogenesis, had not been explored. In this regard, most studies of fungal agents have rightly concentrated on their mycotoxin formation and effects. Recently, the direct role of yeasts and fungi in the etiology of cancers, including leukemia, have been investigated. While greater attention has been placed on the carcinogenic effects of Candida, the role of filamentous fungi in carcinogenesis has also been explored. Recent findings from studies using the enzyme-linked immunosorbent assay (ELISA) technique indicate that the plasma of patients with acute lymphoblastic leukemia (ALL) uniformly contains antibodies for a certain mycovirus-containing Aspergillus flavus, while controls are negative. The exposure of mononuclear leukocytes from patients with ALL in full remission, and long-term survivors, to the product of this organism was reported to result in the re-development of typical genetics and cell surface phenotypes characteristic of active ALL. Mycoviruses are known to be able to significantly alter the biological characteristics and functions of their host. The possible carcinogenic and leukemogenic role of mycoviruses, with and without their host, needs to be further investigated.

Inhibition of Enveloped Virus Surrogate Phi6 Infection Using Yeast-Derived Vacuoles

The periodic emergence of infectious disease poses a serious threat to human life. Among the causative agents, including pathogenic bacteria and fungi, enveloped viruses have caused global pandemics. In the last 10 years, outbreaks of severe acute respiratory syndrome coronavirus 2 disease, severe acute respiratory syndrome, and Middle East respiratory syndrome have all been caused by enveloped viruses. Among several paths of secondary transmission, inhalation of aerosols containing saliva with sputum droplets from infected patients is the major path. To prevent these infectious diseases, mass use of antiviral agents is essential. The yeast-derived vacuole is a small organelle in which hydrolytic enzymes are concentrated. It is an intracellular organ with an excellent ability to process old organelles and bacteria and viruses that have invaded from the outside and can be present in sufficient quantity to be called a kind of enzyme bomb. We confirmed the inhibition of virus infection and structural collapse by vacuole treatment. Among several enzymes, proteases affected Phi6 infectivity. This study tried to isolate these vacuoles from yeast and use them as an antiviral agent for virus treatment, which is a recent issue. We confirmed that viral infectivity was inactivated, and structure collapsed through vacuole treatment. This paper is meaningful in that extracellularly isolated yeast-derived vacuoles are a first attempt to utilize vacuoles for viral treatment. IMPORTANCE The study assesses the vacuoles isolated from the yeast Saccharomyces cerevisiae as green antiviral agents to decrease the concerns about massive use of chemical antiviral agents and its side effects. To prevent the spreading of infectious diseases, personal or public use of antiviral agents is encouraged. The concern about the active compounds of these chemical antiviral agents has grown. Active compounds of antiviral agents have potential side effects on human health and the environment. Our proposed approach suggests effective and green antivirus material from a nonhazardous yeast strain. Also, large-scale production using a fermentation process can allow cost-effectiveness. The results showed sufficient reduced infectivity by vacuole treatment. The exposed vacuole can play the roles of both enzyme bomb to the virus and renewable nutrient source in the ecosystem.

Characterization of the First Alternavirus Identified in Fusarium avenaceum, the Causal Agent of Potato Dry Rot

A novel virus with a double-stranded RNA (dsRNA) genome was isolated from Fusarium avenaceum strain GS-WW-224, the causal agent of potato dry rot. The virus has been designated as Fusarium avenaceum alternavirus 1 (FaAV1). Its genome consists of two dsRNA segments, 3538 bp (dsRNA1) and 2477 bp (dsRNA2) in length, encoding RNA-dependent RNA polymerase (RdRp) and a hypothetical protein (HP), respectively. The virions of FaAV1 are isometric spherical and approximately 30 nm in diameter. Multiple sequence alignments and phylogenetic analyses based on the amino acid sequences of RdRp and HP indicated that FaAV1 appears to be a new member of the proposed family Alternaviridae. No significant differences in colony morphology and spore production were observed between strains GS-WW-224 and GS-WW-224-VF, the latter strain being one in which FaAV1 was eliminated from strain GS-WW-224. Notably, however, the dry weight of mycelial biomass of GS-WW-224 was higher than that of mycelial biomass of GS-WW-224-VF. The depth and the width of lesions on potato tubers caused by GS-WW-224 were significantly greater, relative to GS-WW-224-VF, suggesting that FaAV1 confers hypervirulence to its host, F. avenaceum. Moreover, FaAV1 was successfully transmitted horizontally from GS-WW-224 to ten other species of Fusarium, and purified virions of FaAV1 were capable of transfecting wounded hyphae of the ten species of Fusarium. This is the first report of an alternavirus infecting F. avenaceum and conferring hypervirulence.

Mycoviral gene integration converts a plant pathogenic fungus into a biocontrol agent

Mycovirus-infected fungi can suffer from poor growth, attenuated pigmentation, and virulence. However, the molecular mechanisms of how mycoviruses confer these symptoms remain poorly understood. Here, we report a mycovirus Stemphylium lycopersici alternavirus 1 (SlAV1) isolated from a necrotrophic plant pathogen Stemphylium lycopersici that causes altered colony pigmentation and hypovirulence by specifically interfering host biosynthesis of Altersolanol A, a polyketide phytotoxin. SlAV1 significantly down-regulates a fungal polyketide synthase (PKS1), the core enzyme of Altersolanol A biosynthesis. PKS1 deletion mutants do not accumulate Altersolanol A and lose pathogenicity to tomato and lettuce. Transgenic expression of SlAV1 open-reading frame 3 (ORF3) in S. lycopersici inhibits fungal PKS1 expression and Altersolanol A accumulation, leading to symptoms like SlAV1-infected fungal strains. Multiple plant species sprayed with mycelial suspension of S. lycopersici or S. vesicarium strains integrating and expressing ORF3 display enhanced resistance against virulent strains, converting the pathogenic fungi into biocontrol agents. Hence, our study not only proves inhibiting a key enzyme of host phytotoxin biosynthesis as a molecular mechanism underlying SlAV1-mediated hypovirulence of Stemphylium spp., but also demonstrates the potential of mycovirus-gene integrated fungi as a potential biocontrol agent to protect plants from fungal diseases.

Viral cross-class transmission results in disease of a phytopathogenic fungus

Interspecies transmission of viruses is a well-known phenomenon in animals and plants whether via contacts or vectors. In fungi, interspecies transmission between distantly related fungi is often suspected but rarely experimentally documented and may have practical implications. A newly described double-strand RNA (dsRNA) virus found asymptomatic in the phytopathogenic fungus Leptosphaeria biglobosa of cruciferous crops was successfully transmitted to an evolutionarily distant, broad-host range pathogen Botrytis cinerea. Leptosphaeria biglobosa botybirnavirus 1 (LbBV1) was characterized in L. biglobosa strain GZJS-19. Its infection in L. biglobosa was asymptomatic, as no significant differences in radial mycelial growth and pathogenicity were observed between LbBV1-infected and LbBV1-free strains. However, cross-species transmission of LbBV1 from L. biglobosa to infection in B. cinerea resulted in the hypovirulence of the recipient B. cinerea strain t-459-V. The cross-species transmission was succeeded only by inoculation of mixed spores of L. biglobosa and B. cinerea on PDA or on stems of oilseed rape with the efficiency of 4.6% and 18.8%, respectively. To investigate viral cross-species transmission between L. biglobosa and B. cinerea in nature, RNA sequencing was carried out on L. biglobosa and B. cinerea isolates obtained from Brassica samples co-infected by these two pathogens and showed that at least two mycoviruses were detected in both fungal groups. These results indicate that cross-species transmission of mycoviruses may occur frequently in nature and result in the phenotypical changes of newly invaded phytopathogenic fungi. This study also provides new insights for using asymptomatic mycoviruses as biocontrol agent.

Novel Mycoviruses Discovered from a Metatranscriptomics Survey of the Phytopathogenic Alternaria Fungus

Alternaria fungus can cause notable diseases in cereals, ornamental plants, vegetables, and fruits around the world. To date, an increasing number of mycoviruses have been accurately and successfully identified in this fungus. In this study, we discovered mycoviruses from 78 strains in 6 species of the genus Alternaria, which were collected from 10 pear production areas using high-throughput sequencing technology. Using the total RNA-seq, we detected the RNA-dependent RNA polymerase of 19 potential viruses and the coat protein of two potential viruses. We successfully confirmed these viruses using reverse transcription polymerase chain reaction with RNA as the template. We identified 12 mycoviruses that were positive-sense single-stranded RNA (+ssRNA) viruses, 5 double-strand RNA (dsRNA) viruses, and 4 negative single-stranded RNA (-ssRNA) viruses. In these viruses, five +ssRNA and four -ssRNA viruses were novel mycoviruses classified into diverse the families Botourmiaviridae, Deltaflexivirus, Mymonaviridea, and Discoviridae. We identified a novel -ssRNA mycovirus isolated from an A. tenuissima strain HB-15 as Alternaria tenuissima negative-stranded RNA virus 2 (AtNSRV2). Additionally, we characterized a novel +ssRNA mycovirus isolated from an A. tenuissima strain SC-8 as Alternaria tenuissima deltaflexivirus 1 (AtDFV1). According to phylogenetic and sequence analyses, we determined that AtNSRV2 was related to the viruses of the genus Sclerotimonavirus in the family Mymonaviridae. We also found that AtDFV1 was related to the virus family Deltaflexivirus. This study is the first to use total RNA sequencing to characterize viruses in Alternaria spp. These results expand the number of Alternaria viruses and demonstrate the diversity of these mycoviruses.

Human Clinical Isolates of Pathogenic Fungi Are Host to Diverse Mycoviruses

Fungi host viruses from many families, and next-generation sequencing can be used to discover previously unknown genomes. Some fungus-infecting viruses (mycoviruses) confer hypovirulence on their pathogenic hosts, raising the possibility of therapeutic application in the treatment of fungal diseases. Though all fungi probably host mycoviruses, many human pathogens have none documented, implying the mycoviral catalogue remains at an early stage. Here, we carried out virus discovery on 61 cultures of pathogenic fungi covering 27 genera and at least 56 species. Using next-generation sequencing of total nucleic acids, we found no DNA viruses but did find a surprising RNA virus diversity of 11 genomes from six classified families and two unclassified lineages, including eight genomes likely representing new species. Among these was the first jivivirus detected in a fungal host (Aspergillus lentulus). We separately utilized rolling circle amplification and next-generation sequencing to identify ssDNA viruses specifically. We identified 13 new cressdnaviruses across all libraries, but unlike the RNA viruses, they could not be confirmed by PCR in either the original unamplified samples or freshly amplified nucleic acids. Their distributions among sequencing libraries and inconsistent detection suggest low-level contamination of reagents. This highlights both the importance of validation assays and the risks of viral host prediction on the basis of highly amplified sequencing libraries. Meanwhile, the detected RNA viruses provide a basis for experimentation to characterize possible hypovirulent effects, and hint at a wealth of uncharted viral diversity currently frozen in biobanks. IMPORTANCE Fungal pathogens of humans are a growing global health burden. Viruses of fungi may represent future therapeutic tools, but for many fungal pathogens there are no known viruses. Our study examined the viral content of diverse human-pathogenic fungi in a clinical biobank, identifying numerous viral genomes, including one lineage previously not known to infect fungi.

Hypovirulence of Colletotrichum gloesporioides Associated with dsRNA Mycovirus Isolated from a Mango Orchard in Thailand

The pathogenic fungus Colletotrichum gloeosporioides causes anthracnose disease, which is an important fungal disease affecting the production of numerous crops around the world. The presence of mycoviruses, however, may have an impact on the pathogenicity of the fungal host. Here, we describe a double-stranded RNA (dsRNA) mycovirus, which was isolated from a field strain of C. gloeosporioides, Ssa-44.1. The 2939 bp genome sequence comprises two open reading frames (ORFs) that encode for a putative protein and RNA-dependent RNA polymerase (RdRp). The Ssa-44.1 mycovirus is a member of the unclassified mycovirus family named Colletotrichum gloeosporioides RNA virus 1 strain Ssa-44.1 (CgRV1-Ssa-44.1), which has a phylogenetic similarity to Colletotrichum gleosporioides RNA virus 1 (CgRV1), which was isolated from citrus leaves in China. In C. gloeosporioides, CgRV1-Ssa-44.1 was shown to be linked to hypovirulence. CgRV1-Ssa-44.1 has a low spore transfer efficiency but can successfully spread horizontally to isogenic virus-free isolates. Furthermore, CgRV1-Ssa-44.1 had a strong biological control impact on C. gloeosporioides on mango plants. This study is the first to describe a hypovirulence-associated mycovirus infecting C. gloeosporioides, which has the potential to assist with anthracnose disease biological management.

Going Viral: Virus-Based Biological Control Agents for Plant Protection

The most economically important biotic stresses in crop production are caused by fungi, oomycetes, insects, viruses, and bacteria. Often chemical control is still the most commonly used method to manage them. However, the development of resistance in the different pathogens/pests, the putative damage on the natural ecosystem, the toxic residues in the field, and, thus, the contamination of the environment have stimulated the search for saferalternatives such as the use of biological control agents (BCAs). Among BCAs, viruses, a major driver for controlling host populations and evolution, are somewhat underused, mostly because of regulatory hurdles that make the cost of registration of such host-specific BCAs not affordable in comparison with the limited potential market. Here, we provide a comprehensive overview of the state of the art of virus-based BCAs against fungi, bacteria, viruses, and insects, with a specific focus on new approaches that rely on not only the direct biocidal virus component but also the complex ecological interactions between viruses and their hosts that do not necessarily result in direct damage to the host.

New Insights on the Integrated Management of Plant Diseases by RNA Strategies: Mycoviruses and RNA Interference

RNA-based strategies for plant disease management offer an attractive alternative to agrochemicals that negatively impact human and ecosystem health and lead to pathogen resistance. There has been recent interest in using mycoviruses for fungal disease control after it was discovered that some cause hypovirulence in fungal pathogens, which refers to a decline in the ability of a pathogen to cause disease. Cryphonectria parasitica, the causal agent of chestnut blight, has set an ideal model of management through the release of hypovirulent strains. However, mycovirus-based management of plant diseases is still restricted by limited approaches to search for viruses causing hypovirulence and the lack of protocols allowing effective and systemic virus infection in pathogens. RNA interference (RNAi), the eukaryotic cell system that recognizes RNA sequences and specifically degrades them, represents a promising. RNA-based disease management method. The natural occurrence of cross-kingdom RNAi provides a basis for host-induced gene silencing, while the ability of most pathogens to uptake exogenous small RNAs enables the use of spray-induced gene silencing techniques. This review describes the mechanisms behind and the potential of two RNA-based strategies, mycoviruses and RNAi, for plant disease management. Successful applications are discussed, as well as the research gaps and limitations that remain to be addressed.

Metatranscriptomic Analysis Reveals Rich Mycoviral Diversity in Three Major Fungal Pathogens of Rice

In recent years, three major fungal diseases of rice, i.e., rice blast, rice false smut, and rice-sheath blight, have caused serious worldwide rice-yield reductions and are threatening global food security. Mycoviruses are ubiquitous in almost all major groups of filamentous fungi, oomycetes, and yeasts. To reveal the mycoviral diversity in three major fungal pathogens of rice, we performed a metatranscriptomic analysis of 343 strains, representing the three major fungal pathogens of rice, Pyricularia oryzae, Ustilaginoidea virens, and Rhizoctonia solani, sampled in southern China. The analysis identified 682 contigs representing the partial or complete genomes of 68 mycoviruses, with 42 described for the first time. These mycoviruses showed affinity with eight distinct lineages: Botourmiaviridae, Partitiviridae, Totiviridae, Chrysoviridae, Hypoviridae, Mitoviridae, Narnaviridae, and Polymycoviridae. More than half (36/68, 52.9%) of the viral sequences were predicted to be members of the families Narnaviridae and Botourmiaviridae. The members of the family Polymycoviridae were also identified for the first time in the three major fungal pathogens of rice. These findings are of great significance for understanding the diversity, origin, and evolution of, as well as the relationship between, genome structures and functions of mycoviruses in three major fungal pathogens of rice.

A novel fungal negative-stranded RNA virus related to mymonaviruses in Auricularia heimuer

Here, we report the characterization of a novel (-)ssRNA mycovirus isolated from Auricularia heimuer CCMJ1222, using a combination of RNA-seq, reverse transcription polymerase chain reaction, 5' and 3' rapid amplification of cDNA ends, and Sanger sequencing. Based on database searches, sequence alignment, and phylogenetic analysis, we designated the virus as "Auricularia heimuer negative-stranded RNA virus 1" (AhNsRV1). This virus has a monopartite RNA genome related to mymonaviruses (order Mononegavirales). The AhNsRV1 genome consists of 11,441 nucleotides and contains six open reading frames (ORFs). The largest ORF encodes a putative RNA-dependent RNA polymerase; the other ORFs encode hypothetical proteins with no conserved domains or known function. AhNsRV1 is the first (-)ssRNA virus and the third virus known to infect A. heimuer.

Molecular characterization of a novel victorivirus isolated from Botryosphaeria dothidea, the causal agent of longan leaf spot disease

Mycoviruses are widespread in all major taxonomic groups of filamentous fungi. Previous research has indicated that mycoviruses are associated with the phytopathogenic fungus Botryosphaeria dothidea. In this study, three distinct double-stranded RNA viruses were detected in B. dothidea strain YCLYY11 isolated from a leaf spot of longan (Dimocarpus longana). The results of BLAST analysis revealed that the predicted amino acid sequences of those viruses were similar to those of Botryosphaeria dothidea chrysovirus 1, Botryosphaeria dothidea partitivirus 1, and an apparent novel victorivirus. Sequencing and analysis of the complete genome of the novel victorivirus indicated it is 5218 bp in length and contains two open reading frames (ORFs) that overlap at the tetranucleotide AUGA. BLASTp analysis of the proteins encoded by ORF1 and ORF2 showed that they were most similar to the coat protein and RNA-dependent RNA polymerase of Sphaeropsis sapinea RNA virus 2 (81.37% and 74.09% identical, respectively). A phylogenetic tree showed that the novel virus clustered together with victoriviruses and was separate from members of the other four genera of the family Totiviridae. Based on its genome structure and the results of phylogenetic analysis, we propose that this novel victorivirus should be named "Botryosphaeria dothidea victorivirus 3". This is also the first report of these three mycoviruses coinfecting a strain of B. dothidea.