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A Structured Viroid RNA Serves as a Substrate for Dicer-Like Cleavage To Produce Biologically Active Small RNAs but Is Resistant to RNA-Induced Silencing Complex-Mediated Degradation

Authors :
Carlos Molina
Ann Harris
Ryuta Takeda
Ying Wang
Ralf Bundschuh
Yijun Qi
Biao Ding
Richard S. Nelson
Asuka Itaya
Xuehua Zhong
Source :
Journal of Virology. 81:2980-2994
Publication Year :
2007
Publisher :
American Society for Microbiology, 2007.

Abstract

RNA silencing is a potent means of antiviral defense in plants and animals. A hallmark of this defense response is the production of 21- to 24-nucleotide viral small RNAs via mechanisms that remain to be fully understood. Many viruses encode suppressors of RNA silencing, and some viral RNAs function directly as silencing suppressors as counterdefense. The occurrence of viroid-specific small RNAs in infected plants suggests that viroids can trigger RNA silencing in a host, raising the question of how these noncoding and unencapsidated RNAs survive cellular RNA-silencing systems. We address this question by characterizing the production of small RNAs of Potato spindle tuber viroid (srPSTVds) and investigating how PSTVd responds to RNA silencing. Our molecular and biochemical studies provide evidence that srPSTVds were derived mostly from the secondary structure of viroid RNAs. Replication of PSTVd was resistant to RNA silencing, although the srPSTVds were biologically active in guiding RNA-induced silencing complex (RISC)-mediated cleavage, as shown with a sensor system. Further analyses showed that without possessing or triggering silencing suppressor activities, the PSTVd secondary structure played a critical role in resistance to RISC-mediated cleavage. These findings support the hypothesis that some infectious RNAs may have evolved specific secondary structures as an effective means to evade RNA silencing in addition to encoding silencing suppressor activities. Our results should have important implications in further studies on RNA-based mechanisms of host-pathogen interactions and the biological constraints that shape the evolution of infectious RNA structures.

Details

ISSN :
10985514 and 0022538X
Volume :
81
Database :
OpenAIRE
Journal :
Journal of Virology
Accession number :
edsair.doi.dedup.....b5e19d08172bd4f2082323abc21d3c16
Full Text :
https://doi.org/10.1128/jvi.02339-06