The Function of RNAi in Plant Development

Abstract

The morphological phenotype of mutations in genes required for posttranscriptional gene silencing (PTGS) or RNA interference (RNAi) in Arabidopsis demonstrates that this process is critical for normal development. One way in which RNAi contributes to gene regulation is through its involvement in the biogenesis of trans-acting small interfering RNAs (siRNAs). These endogenous siRNAs are derived from noncoding transcripts that are cleaved by a microRNA (miRNA) and mediate the silencing of protein-coding transcripts. Some protein-coding genes are also subject to miRNA-initiated transitive silencing. Several developmentally important transcription factors regulated by these silencing mechanisms have been identified.

RNAi-mediated viral immunity requires amplification of virus-derived siRNAs in Arabidopsis thaliana

“…2B). This suggests that the RDR-dependent viral siRNAs were produced by the antiviral DCLs, similar to RDR6-dependent transgene siRNAs and tasiRNAs (2,37), and that the low levels of viral siRNAs detected in rdr1 rdr6 and rdr1 rdr2 rdr6 plants were RDR-independent and represented primary viral siRNAs. Notably, CMVf-Δ2b accumulated to much lower levels in rdr1 rdr6 and rdr1 rdr2 rdr6 plants than in dcl2 dcl4 plants (see Fig.…”

“…Plant and fungal RDRs convert transcripts of target genes into dsRNA that is subsequently processed into secondary siRNAs by a Dicer or Dicer-like (DCL) nuclease. In contrast, Caenorhabditis elegans RDRs, such as RRF-1, may directly manufacture secondary siRNAs without dicing a dsRNA precursor (1)(2)(3). The genome of Arabidopsis thaliana encodes six RDRs that are grouped into four clusters (1,2,4), among which little is known about cluster III, consisting of RDRs 3a, 3b, and 3c.…”

“…In contrast, Caenorhabditis elegans RDRs, such as RRF-1, may directly manufacture secondary siRNAs without dicing a dsRNA precursor (1)(2)(3). The genome of Arabidopsis thaliana encodes six RDRs that are grouped into four clusters (1,2,4), among which little is known about cluster III, consisting of RDRs 3a, 3b, and 3c. RDR2 and RDR6 are both required for the short-distance spread of transgene silencing and for the perception, but not the production, of the long-distance mobile silencing signal (1,(5)(6)(7)(8)(9).…”

“…RDR2 is also essential for the biogenesis of the DCL3-dependent 24-nucleotide (nt) repeat-associated siRNAs (rasiRNAs) derived from transposons, retroelements, and other elements, which are the most abundant endogenous small RNAs in A. thaliana (3). Similarly, RDR6 coupled with DCL4 or DCL1 is responsible for the biogenesis of transacting siRNAs (tasiRNAs) and natural antisense siRNAs (nat-siRNAs), which silence expression of their target genes like microRNAs (miRNAs) (1)(2)(3).…”

“…antiviral immunity | cucumber mosaic virus | RNA silencing | RNAdependent RNA polymerase | secondary small interfering RNA R NA silencing or RNA interference in fungi, nematodes and plants requires amplification of small interfering RNAs by eukaryotic RNA-directed RNA polymerases (RDRs) (1)(2)(3). Plant and fungal RDRs convert transcripts of target genes into dsRNA that is subsequently processed into secondary siRNAs by a Dicer or Dicer-like (DCL) nuclease.…”