Molecular Characterization of a Chrysovirus Isolated From the Citrus Pathogen Penicillium crustosum and Related Fungicide Resistance Analysis

Insect hypovirulence-associated mycovirus confers entomopathogenic fungi with enhanced resistance against phytopathogens

Mycoviruses can alter the biological characteristics of host fungi, including change virulence or pathogenicity of phytopathogens and entomopathogenic fungi (EPF). However, most studies on the mycoviruses found in EPF have focused on the effects of the viruses on the virulence of host fungi towards insect pests, with relatively few reports on the effects to the host fungi with regard to plant disease resistance in hosts. The present study investigated the effects of the mycovirus Beauveria bassiana chrysovirus 2 (BbCV2) virus infection on host biological characteristics, evaluated antagonistic activity of BbCV2 against two phytopathogenic fungi (Sclerotinia sclerotiorum and Botrytis cinerea), and transcriptome analysis was used to reveal the interactions between viruses and hosts. Our results showed that BbCV2 virus infection increased B. bassiana's growth rate, spore production, and biomass, it also enhanced the capacity of host fungi and their metabolic products to inhibit phytopathogenic fungi. BbCV2 virus infection reduced the contents of the two pathogens in tomato plants significantly, and transcriptome analysis revealed that the genes related to competition for ecological niches and nutrition, mycoparasitism and secondary metabolites in B. bassiana were significantly up-regulated after viral infection. These findings indicated that the mycovirus infection is an important factor to enhance the ability of B. bassiana against plant disease after endophytic colonization. We suggest that mycovirus infection causes a positive effect on B. bassiana against phytopathogens, which should be considered as a potential strategy to promote the plant disease resistance of EPF.

Greetings from virologists to mycologists: A review outlining viruses that live in fungi

Viruses are genetic elements that parasitize self-replicating cells. Therefore, organisms parasitized by viruses are not limited to animals and plants but also include microorganisms. Among these, viruses that parasitize fungi are known as mycoviruses. Mycoviruses with an RNA genome persistently replicate inside fungal cells and coevolve with their host cells, similar to a cellular organelle. Within host cells, mycoviruses can modulate various fungal characteristics and activities, including pathogenicity and the production of enzymes and secondary metabolites. In this review, we provide an overview of the mycovirus research field as introduction to fungal researchers. Recognition of all genetic elements in fungi aids towards better understanding and control of fungi, and makes fungi a significant model system for studying microorganisms containing multiple genetic elements.

Anastomosis Groups and Mycovirome of Rhizoctonia Isolates Causing Sugar Beet Root and Crown Rot and Their Sensitivity to Flutolanil, Thifluzamide, and Pencycuron

Anastomosis groups (AGs) or subgroups of 244 Rhizoctonia isolates recovered from sugar beet roots with symptoms of root and crown rot were characterized to be AG-A, AG-K, AG-2-2IIIB, AG-2-2IV, AG-3 PT, AG-4HGI, AG-4HGII, and AG-4HGIII, with AG-4HGI (108 isolates, 44.26%) and AG-2-2IIIB (107 isolates, 43.85%) being predominate. Four unclassified mycoviruses and one hundred and one putative mycoviruses belonging to six families, namely Mitoviridae (60.00%), Narnaviridae (18.10%), Partitiviridae (7.62%), Benyviridae (4.76%), Hypoviridae (3.81%), and Botourmiaviridae (1.90%), were found to be present in these 244 Rhizoctonia isolates, most of which (88.57%) contained positive single-stranded RNA genome. The 244 Rhizoctonia isolates were all sensitive to flutolanil and thifluzamide, with average median effective concentration (EC₅₀) value of 0.3199 ± 0.0149 μg·mL^-1 and 0.1081 ± 0.0044 μg·mL^-1, respectively. Among the 244 isolates, except for 20 Rhizoctonia isolates (seven isolates of AG-A and AG-K, one isolate of AG-4HGI, and 12 isolates of AG-4HGII), 117 isolates of AG-2-2IIIB, AG-2-2IV, AG-3 PT, and AG-4HGIII, 107 isolates of AG-4HGI, and six isolates of AG-4HGII were sensitive to pencycuron, with average EC₅₀ value of 0.0339 ± 0.0012 μg·mL^-1. Correlation index (ρ) of cross-resistance level between flutolanil and thifluzamide, flutolanil and pencycuron, and thifluzamide and pencycuron was 0.398, 0.315, and 0.125, respectively. This is the first detailed study on AG identification, mycovirome analysis, and sensitivity to flutolanil, thifluzamide, and pencycuron of Rhizoctonia isolates associated with sugar beet root and crown rot.

Molecular characterization of a novel non-segmented double-stranded RNA mycovirus isolated from Penicillium citrinum strain RCEF7060

Penicillium citrinum is a commonly occurring filamentous fungus with a worldwide distribution. However, no sequence data for viruses in P. citrinum have been reported. Here, we characterized a novel dsRNA virus from the hospital indoor air fungal strain P. citrinum RCEF 7060, which we have named "Penicillium citrinum non-segmented dsRNA virus 1" (PcNRV1). The genome of PcNRV1 dsRNA is 2,895 bp in length and contains two open reading frames encoding a protein with an unknown function in ORF1 and a putative RNA-dependent RNA polymerase (RdRp) in ORF2. Sequence comparisons and phylogenetic analysis showed that PcNRV formed a well-supported independent clade together with members of the proposed genus "Unirnavirus" and was most closely related to Penicillium miczynskii RNA virus 1 (PmRV1), with 76.45% amino acid sequence identity in the RdRp. Thus, PcNRV1 is a novel non-segmented dsRNA mycovirus belonging to the proposed genus "Unirnavirus" and is the first characterized viral sequence from P. citrinum.

A Botybirnavirus Isolated from Alternaria tenuissima Confers Hypervirulence and Decreased Sensitivity of Its Host Fungus to Difenoconazole

Alternaria alternata botybirnavirus 1 (AaBRV1) was isolated from a strain of Alternaria alternata, causing watermelon leaf blight in our previous research. The effect of AaBRV1 on the phenotype of its host fungus, however, was not determined. In the present study, a novel strain of AaBRV1 was identified in A. tenuissima strain TJ-NH-51S-4, the causal agent of cotton Alternaria leaf spot, and designated as AaBRV1-AT1. A mycovirus AaBRV1-AT1-free strain TJ-NH-51S-4-VF was obtained by protoplast regeneration, which eliminated AaBRV1-AT1 from the mycovirus AaBRV1-AT1-infected strain TJ-NH-51S-4. Colony growth rate, spore production, and virulence of strain TJ-NH-51S-4 were greater than they were in TJ-NH-51S-4-VF, while the sensitivity of strain TJ-NH-51S-4 to difenoconazole, as measured by the EC50, was lower. AaBRV1-AT1 was capable of vertical transmission via asexual spores and horizontal transmission from strain TJ-NH-51S-4 to strain XJ-BZ-5-1hyg (another strain of A. tenuissima) through hyphal contact in pairing cultures. A total of 613 differentially expressed genes (DEGs) were identified in a comparative transcriptome analysis between TJ-NH-51S-4 and TJ-NH-51S-4-VF. Relative to strain TJ-NH-51S-4-VF, the number of up-regulated and down-regulated DEGs in strain TJ-NH-51S-4 was 286 and 327, respectively. Notably, the expression level of one DEG-encoding cytochrome P450 sterol 14α-demethylase and four DEGs encoding siderophore iron transporters were significantly up-regulated. To our knowledge, this is the first documentation of hypervirulence and reduced sensitivity to difenoconazole induced by AaBRV1-AT1 infection in A. tenuissima.

A novel hexa-segmented dsRNA mycovirus confers hypovirulence in the phytopathogenic fungus Diaporthe pseudophoenicicola

A novel hexa-segmented double-stranded RNA (dsRNA) mycovirus was isolated and characterized from the filamentous phytopathogenic fungus Diaporthe pseudophoenicicola, and was named Diaporthe pseudophoenicicola chrysovirus 1 (DpCV1). The full-length cDNAs of dsRNA1-6 were 3335, 3030, 3039, 2980, 963, and 780 bp, respectively. Sequence analysis indicated the presence of nine open reading frames (ORFs) in the DpCV1 genome. ORF1 in dsRNA1 putatively encoded the RNA-dependent RNA polymerase (RdRp), and ORF3 in dsRNA2 encoded a capsid protein (CP). The seven remaining ORFs, ORF2 in dsRNA2, ORF4 in dsRNA3, ORF6, 7 in dsRNA4, ORF8 in dsRNA5, and ORF9 in dsRNA6, encoded proteins with unknown functions. Phylogenetic analysis revealed that DpCV1 is closely related to members of the cluster I group within the family Chrysoviridae but formed a separate clade. Importantly, all the six segments of DpCV1 were cured successfully through single spore isolation to obtain the isogenic virus-free strains. DpCV1 can confer hypovirulence to the fungal host of Diaporthe pseudophoenicicola. Compared with the virus-free strain, WC02 harboring the DpCV1 is more sensitive to fungicide prochloraz. Furthermore, the cell wall of DpCV1 infected strain was loose and enlarged. This is the first report of a hexa-segmented tentative chrysovirus in D. pseudophoenicicola. This article is protected by copyright. All rights reserved.