[show abstract][hide abstract] ABSTRACT: Eukaryotic mRNAs that prematurely terminate translation are recognized and degraded by nonsense mediated decay (NMD). This degradation pathway is well studied in animal and yeast cells. The data available imply that NMD also takes place in plants. However, the molecular mechanism of recognition and degradation of plant RNAs containing premature terminator codon (PTC) is not known. Here we report that in plant cells this mechanism involves the recognition of the sizes of the 3'-untranslated regions (3'UTR). Plant 3'UTRs longer than 300 nucleotides induce mRNA instability. Contrary to mammalian and yeast cells, this destabilization does not depend on the presence of any specific sequences downstream of the terminator codon. Unlike nuclear-produced mRNAs, plant virus vector long 3'UTR-containing RNAs, which are synthesized directly in the cytoplasm, are stable and translated efficiently. This shows that RNAs produced in the cytoplasm by viral RNA-dependent RNA polymerase are able to avoid the proposed mechanism.
[show abstract][hide abstract] ABSTRACT: Here, the role of small RNAs is described in (i) cytoplasmic viral RNA silencing; (ii) cellular mRNA silencing via miPHK production. The role of cellular factors such as Dicers, Argonautes, RNA-dependent RNA-polymerase, RNA-polymerase IV and pectin methylesterase are discussed in details. Moreover, silencing suppression by viral proteins/RNAs and silencing as an approach of biotechnology are reviewed.