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Journal of Virology, July 2008, p. 6369-6378, Vol. 82, No. 13
0022-538X/08/$08.00+0     doi:10.1128/JVI.02638-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Hypovirus Papain-Like Protease p48 Is Required for Initiation but Not for Maintenance of Virus RNA Propagation in the Chestnut Blight Fungus Cryphonectria parasitica{triangledown}

Fuyou Deng and Donald L. Nuss*

Center for Biosystems Research, University of Maryland Biotechnology Institute, Shady Grove Campus, 9600 Gudelsky Drive, Rockville, Maryland 20850

Received 12 December 2007/ Accepted 23 April 2008

The prototypic hypovirus CHV1-EP713, responsible for virulence attenuation (hypovirulence) of the chestnut blight fungus Cryphonectria parasitica, encodes two papain-like proteases, p29 and p48. Protein p29 has been shown to be dispensable for hypovirus RNA replication and to act as a suppressor of RNA silencing. Here we describe a role for p48 in hypovirus RNA propagation. CHV1-EP713 infectious cDNA clones in which the p48 coding region was deleted, {Delta}p48, were unable to establish infection in C. parasitica when introduced as a DNA form by transformation or as a coding strand transcript by electroporation. However, the {Delta}p48 mutant virus RNA was rescued when p48 was provided in trans. Surprisingly, the {Delta}p48 mutant viruses retained replication competence in the apparent absence of p48 following transmission to wild-type C. parasitica and successive subculturing. The replicating {Delta}p48 mutant virus was reduced in RNA accumulation by 60% both in the absence and presence of p48 provided in trans and was transmitted through asexual spores (conidia) at a rate 3 to 8% of that for full-length CHV1-EP713. Complementary analysis of strains expressing p48 or containing the replicating {Delta}p48 mutant virus showed that like p29, p48 contributes to virus-mediated suppression of host pigmentation and conidiation, although to a lesser extent, and is dispensable for hypovirus-mediated hypovirulence. The combined results suggest that papain-like protease p48 plays an essential role in the initiation but not the maintenance of virus RNA propagation and also contributes to the regulation of viral RNA accumulation and vertical transmission.

* Corresponding author. Mailing address: Center for Biosystems Reseach, University of Maryland Biotechnology Institute, Shady Grove Campus, 9600 Gudelsky Drive, Rockville, MD 20850. Phone: (240) 314-6218. Fax: (240) 314-6225. E-mail: nuss{at}umbi.umd.edu

{triangledown} Published ahead of print on 30 April 2008.

Journal of Virology, July 2008, p. 6369-6378, Vol. 82, No. 13
0022-538X/08/$08.00+0     doi:10.1128/JVI.02638-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Chiba, S., Salaipeth, L., Lin, Y.-H., Sasaki, A., Kanematsu, S., Suzuki, N. (2009). 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. J. Virol. 83: 12801-12812 [Abstract] [Full Text]  
  • Guo, L.-h., Sun, L., Chiba, S., Araki, H., Suzuki, N. (2009). Coupled termination/reinitiation for translation of the downstream open reading frame B of the prototypic hypovirus CHV1-EP713. Nucleic Acids Res 37: 3645-3659 [Abstract] [Full Text]  
  • Zhang, X., Nuss, D. L. (2008). A host dicer is required for defective viral RNA production and recombinant virus vector RNA instability for a positive sense RNA virus. Proc. Natl. Acad. Sci. USA 105: 16749-16754 [Abstract] [Full Text]  


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