SDE5, the putative homologue of a human mRNA export factor, is required for transgene silencing and accumulation of trans‐acting endogenous siRNA

Abstract

Post-transcriptional gene silencing (PTGS) is a sequence-specific RNA degradation process conserved in fungi, plants and animals. The trigger of the mechanism is double-stranded RNA derived from transgenic or endogenous loci and formed by intra- or inter-molecular interactions of single-stranded RNAs or the action of RNA-dependent RNA polymerases (RDRs). Double-stranded RNA from various sources is processed by one of the four Dicer-like (DCL) proteins in Arabidopsis, and the resulting short RNAs enter into at least four different pathways, one of which involves the production of trans-acting short interfering RNAs (tasiRNAs). We report here a novel gene (SDE5) that is required for transgene silencing and the production of tasiRNAs. Mutation in SDE5 also results in hyper-susceptibility to cucumber mosaic virus but not turnip mosaic virus. However, like RDR6, SDE5 is not involved in inverted repeat-induced transgene silencing or the biogenesis of microRNAs and 24 nt siRNAs produced by DCL3. Based on these results, we propose that SDE5 acts together with RDR6 in generating double-stranded RNA from specific single-stranded RNAs. As the sequence of SDE5 has sequence features shared by TAP, a human mRNA export factor, we propose that its role could be in the transport of RNA molecules that are converted into a double-stranded form by RDR6.

In Planta Recognition of a Double-Stranded RNA Synthesis Protein Complex by a Potexviral RNA Silencing Suppressor

“…In the current model, the dsRNAs synthesized by SGS3/RDR6 are also transported from SGS3/RDR6 bodies into the nucleus (Kumakura et al, 2009;Jouannet et al, 2012). Since SDE5 encodes a putative RNA export protein required for the sense transgene-induced RNA silencing (S-RNAi) and tasiRNA pathways, but not for the inverted repeat transgeneinduced RNA silencing (IR-RNAi), similar to SGS3 and RDR6 (Hernandez-Pinzon et al, 2007;Jauvion et al, 2010), SDE5 may play a role in RNA transport in conjunction with SGS3 and RDR6, although it remains unknown whether SDE5 participates in the export of RNA from the nucleus to the cytoplasm or import from the cytoplasm to the nucleus (Jauvion et al, 2010). Therefore, TGBp1 may interfere with the role of SDE5 to transport RNAs required for the amplification phase of RNA silencing.…”

A Short Open Reading Frame Encompassing the MicroRNA173 Target Site Plays a Role in trans-Acting Small Interfering RNA Biogenesis

“…3B). Although previous studies showed that SDE5 is an essential component in the tasiRNA production pathway and it was proposed that SDE5 functions to import TAS dsRNA from the cytosol to the nucleus or to forward single-stranded RNAs to RDR6 (Hernandez-Pinzon et al, 2007;Jauvion et al, 2010), the roles of SDE5 in the tasiRNA production pathway have remained unclear. Previous epistasis analysis between SGS3 and RDR6 showed that SGS3 plays a crucial role in stabilization of miR173-cleaved fragments (Yoshikawa et al, 2005).…”

“…Subsequently, either cleavage fragment is converted into dsRNAs by RNA-DEPENDENT RNA POLYMERASE6 (RDR6), and processed by DCL4 into 21-nt tasiRNAs that are incorporated by AGO1, AGO2, or AGO5 (Mi et al, 2008;Takeda et al, 2008;Xie et al, 2005;Yoshikawa et al, 2005). SILENCING DEFECTIVE5 (SDE5) was also identified as an essential factor for tasiRNA production (Hernandez-Pinzon et al, 2007;Jauvion et al, 2010). SDE5 is partially homologous to human TAP/NXF1 that participates in mRNA export from the nucleus to the cytoplasm (HernandezPinzon et al, 2007).…”

Antiviral Silencing and Suppression of Gene Silencing in Plants

“…RDR6 activity is facilitated by protein cofactors SUPPRESSOR OF GENE SILENCINIG 3 (SGS3) (Mourrain et al 2000), SILENCING DEFECTIVE 5 (SDE5) (Hernandez-Pinzon et al 2007) and SILENCING DEFECTIVE 3 (SDE3) (Dalmay et al 2001). SGS3, a plant specific protein associate to RISC complex (Allen et al 2005;Yoshikawa et al 2005), stabilizes the RISC-cleavage products following slicing and enhance their conversion into dsRNA by RDR6 (Yoshikawa et al 2013).…”

“…SDE5 acts together with RDR6 to convert ssRNAs into dsRNA. sde5 mutant plants are hypersusceptible to CMV but not to TuMV infection (Hernandez-Pinzon et al 2007). Silencing amplification is facilitated by the SDE3, an RNA-helicase like protein.…”