Open AccessThe p122 Subunit of Tobacco Mosaic Virus Replicase Is a Potent Silencing Suppressor and Compromises both Small Interfering RNA- and MicroRNA-Mediated Pathways
Author(s) -
Tibor Csorba,
Aurelie Bovi,
Tamás Dalmay,
József Burgyán
Publication year - 2007
Publication title -
journal of virology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.617
H-Index - 292
eISSN - 1070-6321
pISSN - 0022-538X
DOI - 10.1128/jvi.01230-07
Subject(s) - trans acting sirna , biology , gene silencing , rna induced silencing complex , rna silencing , small interfering rna , argonaute , rna interference , rna induced transcriptional silencing , rna , microbiology and biotechnology , rna dependent rna polymerase , small rna , microrna , virology , genetics , gene
One of the functions of RNA silencing in plants is to defend against molecular parasites, such as viruses, retrotransposons, and transgenes. Plant viruses are inducers, as well as targets, of RNA silencing-based antiviral defense. Replication intermediates or folded viral RNAs activate RNA silencing, generating small interfering RNAs (siRNAs), which are the key players in the antiviral response. Viruses are able to counteract RNA silencing by expressing silencing-suppressor proteins. It has been shown that many of the identified silencing-suppressor proteins bind long double-stranded RNA or siRNAs and thereby prevent assembly of the silencing effector complexes. In this study, we show that the 122-kDa replicase subunit (p122) of crucifer-infecting Tobacco mosaic virus (cr-TMV) is a potent silencing-suppressor protein. We found that the p122 protein preferentially binds to double-stranded 21-nucleotide (nt) siRNA and microRNA (miRNA) intermediates with 2-nt 3' overhangs inhibiting the incorporation of siRNA and miRNA into silencing-related complexes (e.g., RNA-induced silencing complex [RISC]) both in vitro and in planta but cannot interfere with previously programmed RISCs. In addition, our results also suggest that the virus infection and/or sequestration of the siRNA and miRNA molecules by p122 enhances miRNA accumulation despite preventing its methylation. However, the p122 silencing suppressor does not prevent the methylation of certain miRNAs in hst-15 mutants, in which the nuclear export of miRNAs is compromised.