Synergistic action of the Arabidopsis spliceosome components PRP39a and SmD1b in promoting posttranscriptional transgene silencing.

Besides regulating splicing, the conserved spliceosome component SmD1 (Small nuclear ribonucleoprotein D1)b promotes posttranscriptional silencing of sense transgenes (S-PTGS [post-transcriptional genesilencing]). Here, we show that the conserved spliceosome component PRP39 (Pre-mRNA-processing factor 39)a also plays a role in S-PTGS in Arabidopsis thaliana. However, PRP39a and SmD1b actions appear distinct in both splicing and S-PTGS.

The Nuclear Ribonucleoprotein SmD1 Interplays with Splicing, RNA Quality Control, and Posttranscriptional Gene Silencing in Arabidopsis.

RNA quality control (RQC) eliminates aberrant RNAs based on their atypical structure, whereas posttranscriptional gene silencing (PTGS) eliminates both aberrant and functional RNAs through the sequence-specific action of short interfering RNAs (siRNAs). The Arabidopsis thaliana mutant smd1b was identified in a genetic screen for PTGS deficiency, revealing the involvement of SmD1, a component of the Smith (Sm) complex, in PTGS. The smd1a and smd1b single mutants are viable, but the smd1a smd1b double mutant is embryo-lethal, indicating that SmD1 function is essential.

Regulation of flavonoid biosynthesis involves an unexpected complex transcriptional regulation of TT8 expression, in Arabidopsis.

TT8/bHLH042 is a key regulator of anthocyanins and proanthocyanidins (PAs) biosynthesis in Arabidopsis thaliana. TT8 transcriptional activity has been studied extensively, and relies on its ability to form, with several R2R3-MYB and TTG1 (WD-Repeat protein), different MYB-bHLH-WDR (MBW) protein complexes. By contrast, little is known on how TT8 expression is itself regulated.

Mutations in the Arabidopsis H3K4me2/3 demethylase JMJ14 suppress posttranscriptional gene silencing by decreasing transgene transcription.

Posttranscriptional gene silencing (PTGS) mediated by sense transgenes (S-PTGS) results in RNA degradation and DNA methylation of the transcribed region. Through a forward genetic screen, a mutant defective in the Histone3 Lysine4 di/trimethyl (H3K4me2/3) demethylase Jumonji-C (JmjC) domain-containing protein14 (JMJ14) was identified. This mutant reactivates various transgenes silenced by S-PTGS and shows reduced Histone3 Lysine9 Lysine14 acetylation (H3K9K14Ac) levels, reduced polymerase II occupancy, reduced transgene transcription, and increased DNA methylation in the promoter region, consistent with the hypothesis that high levels of transcription are required to trigger S-PTGS.

RDR2 partially antagonizes the production of RDR6-dependent siRNA in sense transgene-mediated PTGS.

Background: RNA-DEPENDENT RNA POLYMERASE6 (RDR6) and SUPPRESSOR of GENE SILENCING 3 (SGS3) are required for DNA methylation and post-transcriptional gene silencing (PTGS) mediated by 21-nt siRNAs produced by sense transgenes (S-PTGS). In contrast, RDR2, but not RDR6, is required for DNA methylation and TGS mediated by 24-nt siRNAs, and for cell-to-cell spreading of IR-PTGS mediated by 21-nt siRNAs produced by inverted repeat transgenes under the control of a phloem-specific promoter.

Principal Findings: In this study, we examined the role of RDR2 and RDR6 in S-PTGS.

The miRNA pathway limits AGO1 availability during siRNA-mediated PTGS defense against exogenous RNA.

In plants, most microRNAs (miRNAs) and several endogenous small interfering RNAs (siRNAs) bind to ARGONAUTE1 (AGO1) to regulate the expression of endogenous genes through post-transcriptional gene silencing (PTGS). AGO1 also participates in a siRNA-mediated PTGS defense response that thwarts exogenous RNA deriving from viruses and transgenes. Here, we reveal that plants supporting transgene PTGS exhibit increased levels of AGO1 protein.

The conserved RNA trafficking proteins HPR1 and TEX1 are involved in the production of endogenous and exogenous small interfering RNA in Arabidopsis.

We previously identified Arabidopsis thaliana mutants defective in sense transgene posttranscriptional gene silencing (S-PTGS) that defined six loci; here, we describe mutants that define nine additional loci, including HYPER RECOMBINATION1 (HPR1), SILENCING DEFECTIVE3 (SDE3), and SDE5. Our analyses extend previous findings by showing that the requirement for the putative RNA helicase SDE3 is inversely proportional to the strength of the PTGS inducer and that the putative RNA trafficking protein SDE5 is an essential component of the trans-acting small interfering RNA (tasiRNA) pathway and is required for S-PTGS but not inverted repeat transgene-mediated PTGS (IR-PTGS). Our screen also identified HPR1 as a PTGS actor.

Redundant and specific roles of the ARGONAUTE proteins AGO1 and ZLL in development and small RNA-directed gene silencing.

The Arabidopsis ARGONAUTE1 (AGO1) and ZWILLE/PINHEAD/AGO10 (ZLL) proteins act in the miRNA and siRNA pathways and are essential for multiple processes in development. Here, we analyze what determines common and specific function of both proteins. Analysis of ago1 mutants with partially compromised AGO1 activity revealed that loss of ZLL function re-establishes both siRNA and miRNA pathways for a subset of AGO1 target genes.