In plants, double-stranded (ds) RNA that is degraded to small (sm) RNAs that are ∼23 nucleotides in length can trigger the degradation of homologous RNAs in the cytoplasm (posttranscriptional gene silencing or PTGS) and de novo methylation of homologous DNA in the nucleus . PTGS is similar to quelling in fungi  and RNAi in animals . RNA-directed DNA methylation (RdDM) can lead to transcriptional gene silencing (TGS) and the methylation of homologous target promoters if dsRNAs containing promoter sequences are involved . HC-Pro is a plant viral suppressor of PTGS that acts by preventing the accumulation of smRNAs [5, 6] that provide the specificity determinant for homologous RNA degradation [7-10]. Here, we show that HC-Pro does not suppress TGS induced by promoter dsRNA. Moreover, the amount of promoter smRNAs is elevated 5-fold in the presence of HC-Pro, and target promoter methylation is slightly increased without a concomitant rise in the level of promoter dsRNA. The promoter dsRNA, which is not polyadenylated, failed to trigger substantial degradation of polyadenylated, single-stranded promoter RNA. The differential effects of HC-Pro on smRNA accumulation associated with dsRNA-mediated TGS and at least some cases of PTGS suggest that dsRNA processing can occur by alternative pathways, and they support the idea that RdDM is triggered by smRNAs.
|Original language||English (US)|
|Number of pages||5|
|State||Published - Jul 24 2001|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)