RNAi enzyme complexes

In plants, four homologues of the RNA-directed RNA polymerase (RDR) family proteins are likely to be expressed (Fig. 1). RDR1 seems to be directly involved in the defense of certain viruses. RDR2 is involved in nuclear processes and is essential for RNA-directed DNA methylation (RdDM). RDR6 is one of the key enzymes of post-transcriptional gene silencing (PTGS) or RNA interference (RNAi), and is mainly active in the cytoplasm (Fig. 2). So far, no data have been published on the biological function of the plant RDR3 isoforms (RDR3a-3c). To gain further information about the functionality of the RDR2 and RDR6 the corresponding RDR cDNA sequences were isolated from Nicotiana tabacum. Transgene constructs containing the tagged RDR2 and RDR6 are currently introduced into N. tabacum to identify and isolate RNA molecules and protein complexes that are associated with these enzymes. Characterization of these components should help to extend our current knowledge on PTGS and RdDM.

Phylogenetic tree of all currently known plant RNA-directed RNA polymerases (last update December 2005)

Model of post-transcriptional gene silencing (PTGS) in plants with a focus on the function of RNA-directed RNA polymerases (RDRs)

See also: Wassenegger M. and Krczal G. (2006). Nomenclature and functions of RNA-directed RNA polymerases. Trends Plant Sci. 11: 142-151..

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