Showing papers on "Mycovirus published in 1999"

Genetic interrelationships and genome organization of double-stranded RNA elements of Fusarium poae.

Abstract: The similar-sized double-stranded RNA (dsRNA) elements present in vegetatively compatible strains of Fusarium poae were always genetically related, while vegetatively incompatible strains of the fungus contained either homologous or non-homologous dsRNAs of the same size. Electron microscopic observations revealed the co-existence of encapsidated and naked dsRNA elements in the same host. A mycovirus, named FUPO-1 was purified from strain A-11 and was found to contain two kinds of dsRNA segments, dsRNA 1 and dsRNA 2. The dsRNA genome of these segments was converted to cDNA clones by reverse transcription and the clones were subjected to sequence analysis. The single long open reading frame deduced from the sequence of dsRNA 1 showed similarities to the putative coat protein genes known from other mycoviruses, while conserved motifs of an RNA-dependent RNA polymerase were identified in the predicted amino acid sequence of dsRNA 2. The genome organization and certain sequence motifs of FUPO-1 show similarities to that of the Atkinsonella hypoxylon 2H virus and the FusoV mycovirus, members of the Partitiviridae family.

Viruses in Fungal Populations

Abstract: Viruses are nearly ubiquitous throughout the fungal kingdom, occurring in every major fungal group (Buck, 1986). Although first discovered in 1962, within 20 years fungal viruses were found in over 100 species, and may eventually be found in at least 30% of all fungal species (Buck, 1986; Ghabrial, 1980). Other than surveys, the vast majority of research on fungal viruses has been directed towards the interactions of viruses with fungal hosts at the organismal and molecular levels; these aspects of fungal virology have been extensively reviewed (Buck, 1986; Buck, 1998; Ghabrial, 1980; Ghabrial, 1994; Koltin and Leibowitz, 1988; Lemke, 1979b; Molitoris et al., 1979; Nuss and Koltin, 1990; Wickner, 1996).

A new double-stranded RNA mycovirus from Botrytis cinerea

Abstract: A simple double-stranded RNA mycovirus was detected in a wild-type Botrytis cinerea 55k strain. The virus was located in the fungus cytoplasm as free particles of approximately 28 nm in diameter. The mycovirus possesses a single double-stranded genome segment of 1.8 kilobase pairs (kbp) encapsidated within an isometric protein coat whose main structural component is a polypeptide of 68 kDa. Cells infected with this virus showed an important degree of cellular degeneration.

Horizontal transfer of genetic elements in the black Aspergilli

Abstract: The thesis deals with the horizontal transfer of genetic elements in the black Aspergilli . The black Aspergilli form a complex group of asexual species. All share a characteristic black conidiospore color and the ability to efficiently degrade tannin. Selective isolation of all different black Aspergillus types is possible on media with 20% tannin. Tannins can form complexes with proteins, that are difficult to mineralize. Therefore, the strains may have a special niche in the control of the natural nitrogen cycle. Black Aspergilli occur worldwide and especially in warmer regions at high densities. The spores have an efficient aerial distribution, which produces a well-mixed sporebank in soil throughout the world. Under laboratory conditions isogenic lines are capable, after hyphal fusions, to form a heteroplasmic heterokaryon and (transient) diploids. This so-called parasexual cycle can result in recombination via reassortment of chromosomes, mitotic crossing-over and/or exchange of cytoplasmic genetic elements. Most of the natural isolates are heterokaryon incompatible with one another and unable to form a stable heterokaryon. About the exact mechanism of the heterokaryon incompatibility reactions in the black Aspergilli little is known. Confrontations between heterokaryon self-incompatible strains suggest that prefusion genes are involved. The fact that protoplast fusions are partly able to overcome incompatibility reactions suggests that also fusion and postfusion genes are involved. One of the cytoplasmic candidates for horizontal transfer is the mitochondrion. Different mitochondrial haplotypes can be distinguished, corresponding with different black Aspergillus types . No horizontal transfer or recombination of mitochondria was observed in our natural isolates, though in protoplast fusions mitochondria can recombine. In nature new mitochondrial types may result from mutations. Most of the transfer experiments in these thesis were done with cytoplamsic dsRNA mycoviruses. In nature 10% of the population is infected with a variety of different dsRNA fragments of different viral origins. These mycoviruses can cause serious reductions in their host's fitness on traits as spore production and growth rate. Population genetic models predict that deleterious elements should disappear from a population, unless they have an extra way of transfer than just vertical transmission to offspring. Interspecies transfer of mycoviruses with species like Fusarium poae was in our experiments less difficult to achieve (and thus perhaps more likely in nature) than intraspecies transfer between different black Aspergillus types. In a diploid both interchromosomal and intrachromosomal mitotic recombination could take place. However, molecular data suggests that there is little (para)sexual recombination in the black Aspergillus population, in contrast to other presumably asexual fungi tested so far. Recently transposable elements have been found in black Aspergillus strains. These do seem to have transposed between different, quite unrelated strains. Circular intermediates of these transposable elements may also transfer little parts of genomic DNA, which may lead to some recombination. The size of the genetic elements may influence the chance on horizontal transfer during cell contact: no detectable transfer of mitochondria, very little of mycoviruses and some transfer of transposable elements.