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Journal of Virology, February 2009, p. 1332-1340, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01474-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

RNA Silencing against Geminivirus: Complementary Action of Posttranscriptional Gene Silencing and Transcriptional Gene Silencing in Host Recovery{triangledown}

Edgar A. Rodríguez-Negrete, Jimena Carrillo-Tripp, and Rafael F. Rivera-Bustamante*

Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados del IPN, U. Irapuato, Km 9.6 Libramiento Norte, Irapuato, Gto. 36821, México

Received 14 July 2008/ Accepted 14 November 2008

RNA silencing in plants is a natural defense system mechanism against invading nucleic acids such as viruses. Geminiviruses, a family of plant viruses characterized by a circular, single-stranded DNA genome, are thought to be both inducers and targets of RNA silencing. Some natural geminivirus-host interactions lead to symptom remission or host recovery, a process commonly associated with RNA silencing-mediated defense. Pepper golden mosaic virus (PepGMV)-infected pepper plants show a recovery phenotype, which has been associated with the presence of virus-derived small RNAs. The results presented here suggest that PepGMV is targeted by both posttranscriptional and transcriptional gene silencing mechanisms. Two types of virus-related small interfering RNAs (siRNAs) were detected: siRNAs of 21 to 22 nucleotides (nt) in size that are related to the coding regions (Rep, TrAP, REn, and movement protein genes) and a 24-nt population primarily associated to the intergenic regions. Methylation levels of the PepGMV A intergenic and coat protein (CP) coding region were measured by a bisulfite sequencing approach. An inverse correlation was observed between the methylation status of the intergenic region and the concentration of viral DNA and symptom severity. The intergenic region also showed a methylation profile conserved in all times analyzed. The CP region, on the other hand, did not show a defined profile, and its methylation density was significantly lower than the one found on the intergenic region. The participation of both PTGS and TGS mechanisms in host recovery is discussed.

* Corresponding author. Mailing address: Departamento de Ingeniería Genética, Centro de Investigación y de Estudios Avanzados del IPN-U. Irapuato, Km 9.6 Libramiento Norte, Irapuato, Gto. 36821 Mexico. Phone: 52 462 623 9602. Fax: 52 462 624 5846. E-mail: rrivera{at}ira.cinvestav.mx

{triangledown} Published ahead of print on 19 November 2008.

Journal of Virology, February 2009, p. 1332-1340, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01474-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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