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Journal of Virology, December 2008, p. 11851-11858, Vol. 82, No. 23
0022-538X/08/$08.00+0     doi:10.1128/JVI.01343-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Cymbidium Ringspot Virus Harnesses RNA Silencing To Control the Accumulation of Virus Parasite Satellite RNA{triangledown}

Vitantonio Pantaleo1 and József Burgyán2,3*

Istituto di Virologia Vegetale del CNR, 70126, Unità Operativa di Bari, Bari, Italy,1 Agricultural Biotechnology Center, P. O. Box 411, H-2101 Gödöllo, Hungary,2 Istituto di Virologia Vegetale del CNR, Torino, Italy3

Received 26 June 2008/ Accepted 17 September 2008

Cymbidium ringspot virus (CymRSV) satellite RNA (satRNA) is a parasitic subviral RNA replicon that replicates and accumulates at the cost of its helper virus. This 621-nucleotide (nt) satRNA species has no sequence similarity to the helper virus, except for a 51-nt-long region termed the helper-satellite homology (HSH) region, which is essential for satRNA replication. We show that the accumulation of satRNA strongly depends on temperature and on the presence of the helper virus p19 silencing suppressor protein, suggesting that RNA silencing plays a crucial role in satRNA accumulation. We also demonstrate that another member of the Tombusvirus genus, Carnation Italian ringspot virus (CIRV), supports satRNA accumulation at a higher level than CymRSV. Our results suggest that short interfering RNA (siRNA) derived from CymRSV targets satRNA more efficiently than siRNA from CIRV, possibly because of the higher sequence similarity between the HSH regions of the helper and CIRV satRNAs. RNA silencing sensor RNA carrying the putative satRNA target site in the HSH region was efficiently cleaved when transiently expressed in CymRSV-infected plants but not in CIRV-infected plants. Strikingly, replacing the CymRSV HSH box2 sequence with that of CIRV restores satRNA accumulation both at 24°C and in the absence of the p19 suppressor protein. These findings demonstrate the extraordinary adaptation of this virus to its host in terms of harnessing the antiviral silencing response of the plant to control the virus parasite satRNA.

* Corresponding author. Mailing address: Istituto di Virologia Vegetale del CNR, Strada delle Cacce, 73 Torino 10135, Italy. Phone: 390113488775. Fax: 39011-343-809. E-mail: burgyan{at}abc.hu or J.Burgyan{at}ivv.cnr.it

{triangledown} Published ahead of print on 24 September 2008.

Journal of Virology, December 2008, p. 11851-11858, Vol. 82, No. 23
0022-538X/08/$08.00+0     doi:10.1128/JVI.01343-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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