Satellite and defective RNAs of Cryphonectria hypovirus 3-grand haven 2, a virus species in the family Hypoviridae with a single open reading frame.
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Cryphonectria parasitica hypovirus 3-Grand Haven 2 (CHV3-GH2) is the most recently characterized member of the Hypoviridae family of viruses associated with hypovirulence of the chestnut blight fungus. Isolates of CHV3-GH2 contain either three or four double-stranded (ds) RNAs that are visible on ethidium bromide-stained agarose or polyacrylamide gels. Only the largest dsRNA appears to be required for virus infectivity, and was characterized previously (C. D. Smart et al., 1999, Virology 265, 66-73). In this study, we report the cloning, sequencing, and analysis of the other three dsRNAs. Sizes of the accessory dsRNAs are 3.6 kb (dsRNA 2), 1.9 kb (dsRNA 3), and 0.9 kb (dsRNA 4), compared to 9.8 kb for the genomic dsRNA segment (dsRNA 1). All three accessory dsRNA species are polyadenylated on the 3'-end of one strand, as is genomic dsRNA. DsRNA 2 represents a defective form of dsRNA 1, with the 5'-terminal 1.4 kb derived from the 5'-end of dsRNA 1 and the 3'-terminal 2.2 kb from the 3'-end of dsRNA 1. A single major open reading frame (ORF) is evident from deduced translations of dsRNA 2. The deduced translation product is a 91-kDa protein that represents a fusion consisting of the entire N-terminal protease and the entire putative helicase domain. DsRNAs 3 and 4 represent satellite RNAs that share very little sequence with dsRNA 1 and 2. DsRNA 4 is 937 nucleotides, excluding the poly(A)(+). The first AUG of the polyadenylated strand of dsRNA 4 occurs eight residues in from the 5'-terminus and would initiate the largest ORF on dsRNA 4, with the coding capacity for a 9.4-kDa protein. Within the deduced ORF and approximately 100 nucleotides from the 5'-end of dsRNA 4 is a 22-base sequence that is identical to sequences found in the nontranslated leaders of dsRNAs 1 and 2. DsRNA 3 accumulation in infected cultures varied, but it was less abundant than dsRNA 4. DsRNA 3 was found to represent a head-to-tail dimer of dsRNA 4 linked by a poly(A)/(U) stretch of 40-70 residues. (+info)
Podospora anserina mutant defective in protoperithecium formation, ascospore germination, and cell regeneration.
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A mutant (modx) was selected on the basis of the suppression of self-lysis due to a recessive mutation (modB). modx, a dominant mutation, reduced hyphal branching from nonapical cells, abolished protoperithecium formation, and induced the death of stationary cells only when these were isolated to obtain further development. Mutant ascospores, formed in the fruiting bodies which occasionally occur under specific conditions (32 degrees C on starved medium), showed a delay in the germination process (up to 3 months instead of about 5 h for wild-type ascospores) when submitted to incubation under standard conditions (26 degrees C on germination medium) and failed to germinate at 18 degrees C. Revertants from modx strains, selected on the basis of the suppression of the nonrenewal of growth from stationary cells, were wild type for all the other three defects. Indirect arguments suggested that the modx mutant strain might be defective in the control of a specific class of stable messenger ribonucleic acids which would be essential for the physiology of ascospores and stationary cells. (+info)
The molecular mechanism of protoplasmic incompatibility and its relationship to the formation of protoperithecia in Podospora anserina.
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In Podospora anserina, protoplasmic incompatibility due to interactions between non-allelic genes was suppressed by the effect of mutations in two modifier genes, mod-I and mod-2. It is shown that mod-I and mod-2 are involved in the production of three specific proteins, a phenoloxidase and two previously identified proteases (Begueret & Bernet 1973 a) which are associated with the phenomenon of protoplasmic disintegration. These enzymes, whose messengers are normallly latent during vegetative growth, appear at this stage of the life cycle only as a consequence of incompatible gene interactions. The mode-I and mod-2 genes and each of the five incompatibility loci involved in non-allelic incompatibility systems also participate in the formation of the protoperithecia. This pleiotropic effect suggests that protoplasmic incompatibility is a deviation in the normal physiological processes of protoperithecial formation. (+info)
Ultrastructure of developing ascospores in Sordaria brevicollis.
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The ultrastructure of ascospore wall formation in the pyrenomycete Sordaria brevicollis was studied in developing asci at progressive time intervals. From early spore delimitation through final stage of maturation, the wall of the ascospore differentiated into four composite layers, the periascosporium the delineation ascosporium, the subascosproium, and the endoascosproium, While ascospores were at the hyaline stage of development,they possessed only the periascosporium and delineation ascosporium as their wall components. At about 7 to 8 days from the initiation of the cross, the spores developed a yellow color, and this coloration was always associated with the elaboration of the subascorsporium just internal to the ascosporium. Asthe spores continued to progressively darken in color, the subascosporium was seen to increase in complexity, electron density, and thickness. Soon after the formation of the subascosporium, the endoascosporium began to develop de novo and was, therefore, the last wall layer formed as the spore approached maturity. (+info)
Biological control of chestnut blight: an example of virus-mediated attenuation of fungal pathogenesis.
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Environmental concerns have focused attention on natural forms of disease control as potentially safe and effective alternatives to chemical pesticides. This has led to increased efforts to develop control strategies that rely on natural predators and parasites or that involve genetically engineered microbial pest control agents. This review deals with a natural form of biological control in which the virulence of a fungal pathogen is attenuated by an endogenous viral RNA genetic element: the phenomenon of transmissible hypovirulence in the chestnut blight fungus, Cryphonectria parasitica. Recent progress in the molecular characterization of a hypovirulence-associated viral RNA has provided an emerging view of the genetic organization and basic expression strategy of this class of genetic elements. Several lines of evidence now suggest that specific hypovirulence-associated virus-encoded gene products selectively modulate the expression of subsets of fungal genes and the activity of specific regulatory pathways. The construction of an infectious cDNA clone of a hypovirulence-associated viral RNA represents a major advancement that provides exciting new opportunities for examining the molecular basis of transmissible hypovirulence and for engineering hypovirulent strains for improved biocontrol. These developments have significantly improved the prospects of using this system to identify molecular determinants of virulence and elucidate signal transduction pathways involved in pathogenic responses. In addition, novel approaches are now available for extending the application of transmissible hypovirulence for management of chestnut blight and possibly other fungal diseases. (+info)
A viral gene confers hypovirulence-associated traits to the chestnut blight fungus.
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A viral double-stranded (ds)RNA associated with reduced virulence (hypovirulence) and the accompanying biological control of the chestnut blight fungus, Cryphonectria parasitica, was shown recently to contain two contiguous coding domains designated ORF A and ORF B. We report here that transformation of an isogenic virulent, dsRNA-free C. parasitica strain with a cDNA copy of ORF A conferred traits similar to those exhibited by the dsRNA-containing hypovirulent strain: characteristics included reduced pigmentation, reduced laccase accumulation and suppressed conidiation. However virulence was not reduced, indicating an apparent uncoupling of associated traits from hypovirulence. These results establish a direct cause and effect relationship between a viral dsRNA genetic element present in a hypovirulent C. parasitica strain and specific phenotypic traits. They demonstrate further that these traits are not the result of a general reaction of the fungus to the presence of the replicating viral RNA, but are caused by a specific viral coding domain. (+info)
New Hypoxylon and Nemania species from Costa Rica and Taiwan.
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Six xylariaceous fungi, including two Hypoxylon taxa and four Nemania taxa, are described as new. They were collected from either Costa Rica or Taiwan. Two of the Nemania species--N. flavitextura and N. primolutea--were cultured and typical Geniculosporium anamorphs were produced. (+info)
Molecular phylogeny of Hypoxylon and closely related genera.
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Phylogenetic relationships were inferred among several xylariaceous genera with Nodulisporium or nodulisporium-like anamorphs based on the analyses of beta-tubulin and alpha-actin sequences. One hundred nine cultures and three specimens of 83 representatives of these four genera were included in the study. Biscogniauxia taxa formed a well supported clade that was basal to the other taxa, while taxa of Hypoxylon and Daldinia comprised a large monophyletic group that contained two subclades. The first subclade encompassed Hypoxylon sect. Annulata and is accepted here as the new genus Annulohypoxylon. The second subclade contained taxa of Hypoxylon sect. Hypoxylon and Daldinia. Hypoxylon is restricted to include only those taxa in sect. Hypoxylon. Thirty-three epithets are made in Annulohypoxylon. Hypoxylon cohaerens var. microsporum is raised to the species level and accepted as A. minutellum. Hypoxylon polyporoideum is recognized as distinct from H. crocopeplum. Hypoxylon placentiforme is accepted as Daldinia placentiformis. (+info)