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Eukaryotic Cell, June 2006, p. 896-904, Vol. 5, No. 6
1535-9778/06/$08.00+0     doi:10.1128/EC.00373-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Hypovirus Papain-Like Protease p29 Suppresses RNA Silencing in the Natural Fungal Host and in a Heterologous Plant System

Gerrit C. Segers,1,{dagger} Rene van Wezel,2,{ddagger} Xuemei Zhang,2,§ Yiguo Hong,2 and Donald L. Nuss1*

Center for Biosystems Research, University of Maryland Biotechnology Institute, College Park, Maryland 20742-4450,1 Warwick HRI, University of Warwick, Warwick CV35 9EF, United Kingdom2

Received 19 December 2005/ Accepted 12 April 2006

Virulence-attenuating hypoviruses of the species Cryphonectria hypovirus 1 (CHV1) encode a papain-like protease, p29, that shares similarities with the potyvirus-encoded suppressor of RNA silencing HC-Pro. We now report that hypovirus CHV1-EP713-encoded p29 can suppress RNA silencing in the natural host, the chestnut blight fungus Cryphonectria parasitica. Hairpin RNA-triggered silencing was suppressed in C. parasitica strains expressing p29, and transformation of a transgenic green fluorescent protein (GFP)-silenced strain with p29 resulted in an increased number of transformants with elevated GFP expression levels. The CHV1-EP713 p29 protein was also shown to suppress both virus-induced and agroinfiltration-induced RNA silencing and systemic spread of silencing in GFP-expressing transgenic Nicotiana benthamiana line 16c plants. The demonstration that a mycovirus encodes a suppressor of RNA silencing provides circumstantial evidence that RNA silencing in fungi may serve as an antiviral defense mechanism. The observation that a phylogenetically conserved protein of related plant and fungal viruses functions as a suppressor of RNA silencing in both fungi and plants indicates a level of conservation of the mechanisms underlying RNA silencing in these two groups of organisms.

* Corresponding author. Mailing address: Center for Biosystems Research, University of Maryland Biotechnology Institute, Plant Sciences Building, Room 5115, College Park, MD 20742-4450. Phone: (301) 405-0334. Fax: (301) 314-9075. E-mail: nuss{at}umbi.umd.edu.

{dagger} Present address: Monsanto Company, Chesterfield, MO 63017.

{ddagger} Present address: East Malling Research, East Malling, Kent ME19 6BJ, United Kingdom.

§ Present address: Chengdu Institute of Biological Products, Sichuan 610023, China.

Eukaryotic Cell, June 2006, p. 896-904, Vol. 5, No. 6
1535-9778/06/$08.00+0     doi:10.1128/EC.00373-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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