Showing papers on "Mycovirus published in 2009"

Viruses of plant pathogenic fungi.

Abstract: Mycoviruses are widespread in all major groups of plant pathogenic fungi. They are transmitted intracellularly during cell division, sporogenesis, and cell fusion, but apparently lack an extracellular route for infection. Their natural host ranges are limited to individuals within the same or closely related vegetative compatibility groups. Recent advances, however, allowed the establishment of experimental host ranges for a few mycoviruses. Although the majority of known mycoviruses have dsRNA genomes that are packaged in isometric particles, an increasing number of usually unencapsidated mycoviruses with positive-strand RNA genomes have been reported. We discuss selected mycoviruses that cause debilitating diseases and/or reduce the virulence of their phytopathogenic fungal hosts. Such fungal-virus systems are valuable for the development of novel biocontol strategies and for gaining an insight into the molecular basis of fungal virulence. The availability of viral and host genome sequences and of transformation and transfection protocols for some plant pathogenic fungi will contribute to progress in fungal virology.

Mycoviruses of filamentous fungi and their relevance to plant pathology

Abstract: Mycoviruses (fungal viruses) are reviewed with emphasis on plant pathogenic fungi. Based on the presence of virus-like particles and unencapsidated dsRNAs, mycoviruses are common in all major fungal groups. Over 80 mycovirus species have been officially recognized from ten virus families, but a paucity of nucleic acid sequence data makes assignment of many reported mycoviruses difficult. Although most of the particle types recognized to date are isometric, a variety of morphologies have been found and, additionally, many apparently unencapsidated dsRNAs have been reported. Until recently, most characterized mycoviruses have dsRNA genomes, but ssRNA mycoviruses now constitute about one-third of the total. Two hypotheses for the origin of mycoviruses of plant pathogens are discussed: the first that they are of unknown but ancient origin and have coevolved along with their hosts, the second that they have relatively recently moved from a fungal plant host into the fungus. Although mycoviruses are typically readily transmitted through asexual spores, transmission through sexual spores varies with the host fungus. Evidence for natural horizontal transmission has been found. Typically, mycoviruses are apparently symptomless (cryptic) but beneficial effects on the host fungus have been reported. Of more practical interest to plant pathologists are those viruses that confer a hypovirulent phenotype, and the scope for using such viruses as biocontrol agents is reviewed. New tools are being developed based on host genome studies that will help to address the intellectual challenge of understanding the fungal-virus interactions and the practical challenge of manipulating this relationship to develop novel biocontrol agents for important plant pathogens.

A novel bipartite double-stranded RNA Mycovirus from the white root rot Fungus Rosellinia necatrix: molecular and biological characterization, taxonomic considerations, and potential for biological control.

Abstract: White root rot, caused by the ascomycete Rosellinia necatrix, is a devastating disease worldwide, particularly in fruit trees in Japan. Here we report on the biological and molecular properties of a novel bipartite double-stranded RNA (dsRNA) virus encompassing dsRNA-1 (8,931 bp) and dsRNA-2 (7,180 bp), which was isolated from a field strain of R. necatrix, W779. Besides the strictly conserved 5' (24 nt) and 3' (8 nt) terminal sequences, both segments show high levels of sequence similarity in the long 5' untranslated region of approximately 1.6 kbp. dsRNA-1 and -2 each possess two open reading frames (ORFs) named ORF1 to -4. Although the protein encoded by 3'-proximal ORF2 on dsRNA-1 shows sequence identities of 22 to 32% with RNA-dependent RNA polymerases from members of the families Totiviridae and Chrysoviridae, the remaining three virus-encoded proteins lack sequence similarities with any reported mycovirus proteins. Phylogenetic analysis showed that the W779 virus belongs to a separate clade distinct from those of other known mycoviruses. Purified virions approximately 50 nm in diameter consisted of dsRNA-1 and -2 and a single major capsid protein of 135 kDa, which was shown by peptide mass fingerprinting to be encoded by dsRNA-1 ORF1. We developed a transfection protocol using purified virions to show that the virus was responsible for reduction of virulence and mycelial growth in several host strains. These combined results indicate that the W779 virus is a novel bipartite dsRNA virus with potential for biological control (virocontrol), named Rosellinia necatrix megabirnavirus 1 (RnMBV1), that possibly belongs to a new virus family.

Molecular characterization of a dsRNA mycovirus, Fusarium graminearum virus-DK21, which is phylogenetically related to hypoviruses but has a genome organization and gene expression strategy resembling those of plant potex-like viruses.

Abstract: Fusarium graminearum causes a serious scab disease of small grains in Korea. The nucleotide sequence of the genomic RNA of a double-stranded RNA (dsRNA) virus, Fusarium graminearum virus-DK21 (FgV-DK21), from F. graminearum strain DK21, which is associated with hypovirulence in F. graminearum, was determined and compared to the genome sequences of other mycoviruses, including Cryponectria hypoviruses. The FgV-DK21 dsRNA consists of 6,621 [corrected] nucleotides, excluding the 3'-terminal poly(A) tail. The viral genome has 53- and 46-nucleotide 5' and 3' untranslated regions (UTRs), respectively, and four [corrected] putative open reading frames. A phylogenetic analysis of the deduced amino acid sequence of ORF1, which encodes a putative RNA-dependent RNA polymerase, and those of other mycoviruses revealed that this organism forms a distinct virus clade with other hypoviruses, and is more distantly related to other mycoviruses (3.8 to 24.0% identity). However, pairwise sequence comparisons of the nucleotide and deduced amino acid sequences of ORFs 2 through 4 [corrected] revealed no close relationships to other protein sequences currently available in GenBank. Analyses of RNA accumulation by Northern blot and primer extension indicated that these putative gene products are expressed from at least two different subgenomic RNAs (sgRNAs), in contrast to the cases in other hypoviruses. This study suggests the existence of a new, as yet unassigned, genus of mycoviruses that exhibits a potex-like genome organization and sgRNA accumulation.

Mycoviruses are common among different species of endophytic fungi of grasses

Abstract: A survey of mycoviruses was made in a collection of 103 isolates belonging to 53 different species of endophytic fungi of grasses. Double-stranded RNA (dsRNA) elements were detected in isolates of 12 of the species analyzed. The banding characteristics and sizes of some of the dsRNA elements suggest that they might belong to previously described mycovirus families. The observed incidence (22.6%) indicates that the presence of mycoviruses could be common among species of this group of ubiquitous fungi.

Complete nucleotide sequence of double-stranded RNA viruses from Fusarium graminearum strain DK3.

Abstract: The complete genomes two different dsRNA mycoviruses, Fusarium graminearum virus 3 (FgV3) and Fusarium graminearum virus 4 (FgV4), was sequenced and analyzed. The viral genome of FgV3 is 9,098 base pairs (bp) long and contains two open reading frames (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) and a protein of unknown function. The FgV4 genome is composed of two dsRNA genome segments of 2,383 bp and 1,739 bp. FgV4 dsRNA-1 contains a single ORF, which has a conserved RdRp motif, while FgV4 dsRNA-2 contains two putative ORFs coding for products of unknown function. Both the genome organization and phylogenetic analysis indicated that FgV3 was closely related to members of the families Totiviriridae and Chrysoviridae, but it was placed outside of their main clusters, whereas FgV4 formed a distinct clade with the family Partitiviridae. This is the first report of the full-length nucleotide sequences of FgV3 and FgV4 infecting Fusarium graminearum.

A novel virus that infecting hypovirulent strain XG36-1 of plant fungal pathogen Sclerotinia sclerotiorum.

Abstract: Sclerotinia sclerotiorum is a notorious plant fungal pathogen which spreads across the world. Hypovirulence is a phenomenon where the virulence of fungal pathogens is decreased, even lost, due to mycovirus infection. The potential of hypoviruses for biological control of the chestnut blight fungus (Cryphonectria parasitica) has attracted much interest, and has led to discovery of new hypovirulent strains in other fungi. A hypovirulent strain, strain XG36-1, was isolated from a typical lesion on the stem of rapeseed (Brassica napus) caused by Sclerotinia sclerotiorum. Strain XG36-1 grew on PDA very slowly (average 2.5 ± 0.1 mm/d) with sectoring, and developed abnormal colony morphology with few sclerotia. Unlike health strains (such as wildtype strain XG-13), it was unable to induce lesions on detached leaves of rapeseed. Sclerotia of strain XG36-1 produced apothecia rarely. A sexual progeny test showed that the phenotypes of all 104 sexual progeny were not different from wildtype strain XG-13 which shows normal phenotype of S. sclerotiorum, and protoplast regeneration tests showed that 25.5% of the regenerants of strain XG36-1 were recovered fully. Furthermore, the hypovirulence and its associated traits could be transmitted to XG36-1A34 R , a hygromycin-resistance gene labelled sexual progeny of strain XG36-1, by hyphal anastomosis. Transmission electron microscope (TEM) observation showed that the cytoplasm of strain XG36-1 was destroyed and granulated; the membranes of nuclei and mitochondria were disintegrated; and mitochondrial cristae were cavitated. Viral particles (about 40 nm) in hyphae of strain XG36-1, but not in its sexual progeny and wildtype strain XG-13, could be observed with TEM, and several virus-like particles were uniquely enveloped by single layer membrane in the cells of strain XG36-1. Furthermore, the viral particles could be co-transmitted with the hypovirulence traits through hyphal anastomosis. Hypovirulence and its associated traits of strain XG36-1 could be mediated by a fungal virus. Currently, we could not know the characteristic of this virus, but it likely represent a new type of mycovirus in S. sclerotiorum, and possibly in fungi.

Molecular characterisation of two novel double-stranded RNA elements from Phlebiopsis gigantea

Abstract: The incomplete sequences of two large, 10–12 kbp, double-stranded RNAs (dsRNAs) found in the TW-2 isolate of the saprophytic fungus, Phlebiopsis gigantea (Pg) are reported. Both PgV-TW2 dsRNA1 and dsRNA2 potentially encode fusion proteins which are apparently expressed by a translational frameshifting mechanism. The C-terminal region of both predicted proteins was 21% identical and contained the eight motifs conserved in RNA-dependent RNA polymerases of dsRNA mycoviruses and had highest similarity with members of the family Totiviridae, but possibly do not form virions. The remainder of the N-terminal protein sequences predicted from the PgV-TW2 dsRNA1 and dsRNA2 sequences and the 3′-terminal nucleotide sequences of both dsRNAs had no homology with one another or any sequence in the database suggesting that individually both may be members of novel families of mycoviruses.

Novel mycovirus, attenuated strain of phytopathogenic fungus, plant disease controlling agent, method of producing mycovirus, method of attenuating phytopathogenic fungus and method of controlling plant disease

Abstract: The present invention provides a novel mycovirus that suppresses phytopathogenic fungi and a novel method for controlling plant diseases A novel mycovirus that is present endogenously in a predetermined rice blast fungus, has four types of double-stranded RNAs of 28 to 36 kb, and suppresses a phytopathogenic fungus has been found This virus suppresses phytopathogenic fungi such as rice blast fungus

Molecular tools for studying the interaction between Botrytis and the viruses BVX and BVF (NZ).

Abstract: Understanding the nature of the relationship between viruses and their fungal hosts is critical in determining the ecological significance of mycoviruses and their potential usage as biological control agents. Two flexuous viruses belonging to the family Flexiviridae, Botrytis virus F (BVF) and Botrytis virus X (BVX), from Botrytis cinerea have previously been completely sequenced, providing the opportunity to examine their interaction with B. cinerea at molecular level. In addition, studying their impact on the virulence of Botrytis is also of great interest. In order to study the fungus/virus interaction four basic tools were developed: i) an efficient transfection protocol to introduce viruses into uninfected fungal isolates (ii) a transformation protocol to incorporate plasmid DNA into Botrytis, iii) a consistent and reliable real-time PCR detection method for BVF and BVX to study the effect of virus transfections, and iv) an immunoassay for BVX to visualize the virus distribution and movement within the mycelia and also between compatible fungal strains. These tools will enable the study of the relationship between the fungus and the mycoviruses at the cellular level.