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A Dicer-Independent Route for Biogenesis of siRNAs that Direct DNA Methylation in Arabidopsis

ABSTRACT: DNA methylation directed by 24-nucleotide (nt) small interfering RNAs (siRNAs) plays critical roles in gene regulation and transposon silencing in Arabidopsis. Twenty-four-nt siRNAs are known to be processed from double-stranded RNAs by Dicer-like 3 (DCL3) and loaded into the effector Argonaute 4 (AGO4). Here we report a distinct class of siRNAs independent of DCLs (sidRNAs). sidRNAs are present as ladders of ~20 to 60nt in length, often having same 5' ends but differing in 3' ends by 1-nt steps. We further show that sidRNAs are associated with AGO4 and capable of directing DNA methylation. Finally we show that sidRNA production depends on AGO4 and distributive 3'-5' exonucleases. Our findings suggest an alternative route for siRNA biogenesis: precursor transcripts are bound by AGO4 and subsequently subjected to 3'-5' exonucleolytic trimming for maturation. We propose that sidRNAs generated through this route are the initial triggers of de novo DNA methylation.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE74398 | GEO | 2015/12/17

SECONDARY ACCESSION(S): PRJNA300285

REPOSITORIES: GEO

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A Dicer-Independent Route for Biogenesis of siRNAs that Direct DNA Methylation in Arabidopsis

Project description:DNA methylation directed by 24-nucleotide (nt) small interfering RNAs (siRNAs) plays critical roles in gene regulation and transposon silencing in Arabidopsis. Twenty-four-nt siRNAs are known to be processed from double-stranded RNAs by Dicer-like 3 (DCL3) and loaded into the effector Argonaute 4 (AGO4). Here we report a distinct class of siRNAs independent of DCLs (sidRNAs). sidRNAs are present as ladders of ~20 to 60nt in length, often having same 5' ends but differing in 3' ends by 1-nt steps. We further show that sidRNAs are associated with AGO4 and capable of directing DNA methylation. Finally we show that sidRNA production depends on AGO4 and distributive 3'-5' exonucleases. Our findings suggest an alternative route for siRNA biogenesis: precursor transcripts are bound by AGO4 and subsequently subjected to 3'-5' exonucleolytic trimming for maturation. We propose that sidRNAs generated through this route are the initial triggers of de novo DNA methylation. Small RNAs were profiled in Arabidopsis wild type (Col-0), dcl1/2/3/4 and other mutants by Illumina high-throughput sequencing, to identify siRNAs independent of DCLs (sidRNAs) and dissect their biogenesis pathway. DNA methylation was profiled in various mutants by whole-genome bisulfite sequencing to establish a role for sidRNAs in DNA methylation

2015-12-17 | E-GEOD-74398 | biostudies-arrayexpress

AGO4 slicer activity reveals the passenger strand function of plant 23 nt siRNAs and the post-slicing retention of target RNAs mediating RNA-directed DNA methylation [WGBS]

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2023-02-17 | GSE201234 | GEO

AGO4 slicer activity reveals the passenger strand function of plant 23 nt siRNAs and the post-slicing retention of target RNAs mediating RNA-directed DNA methylation [smallRNA-seq]

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RNA-directed DNA methylation involves co-transcriptional small RNA-guided slicing of Pol V transcripts in Arabidopsis

Project description:Small RNAs regulate chromatin modifications such as DNA methylation and gene silencing across eukaryotic genomes. In plants, RNA-directed DNA methylation (RdDM) requires 24-nucleotide (nt) small RNAs (siRNAs) that bind ARGONAUTE4 (AGO4) and target genomic regions for silencing. It also requires non-coding RNAs transcribed by RNA POLYMERASE V (Pol V), although their function is largely unknown. We utilized a modified global nuclear run-on (GRO) protocol followed by deep sequencing to capture Pol V nascent transcripts genome-wide. We uncovered unique characteristics of Pol V RNAs, including a uracil (U) common at position 10. This uracil was complementary to the 5’ adenine found in many AGO4-bound 24-nt siRNAs and was eliminated in an siRNA-deficient mutant. This indicates co-transcriptional slicing of Pol V transcripts by AGO4-bound siRNAs. Pol V transcript slicing also required the elongation factor SPT5L. These results highlight a novel step in RNA-mediated transcriptional gene silencing, which is a conserved process in many eukaryotes.

2018-01-29 | GSE100010 | GEO

RNA-directed DNA methylation involves co-transcriptional small RNA-guided slicing of Pol V transcripts in Arabidopsis.

Project description:Small RNAs regulate chromatin modifications such as DNA methylation and gene silencing across eukaryotic genomes. In plants, RNA-directed DNA methylation (RdDM) requires 24-nucleotide (nt) small RNAs (siRNAs) that bind ARGONAUTE4 (AGO4) and target genomic regions for silencing. It also requires non-coding RNAs transcribed by RNA POLYMERASE V (Pol V), that likely serve as scaffolds for binding of AGO4/siRNA complexes. Here we utilized a modified global nuclear run-on (GRO) protocol followed by deep sequencing to capture Pol V nascent transcripts genome-wide. We uncovered unique characteristics of Pol V RNAs, including a uracil (U) common at position 10. This uracil was complementary to the 5’ adenine found in many AGO4-bound 24-nt siRNAs and was eliminated in an siRNA-deficient mutant as well as in the ago4/6/9 triple mutant, suggesting that the +10U signature is due to siRNA-mediated co-transcriptional slicing of Pol V transcripts. Expressing wild-type AGO4 in ago4/6/9 was able to restore slicing of Pol V transcripts but a catalytically inactive AGO4 mutant did not correct the slicing defect. We also found that Pol V transcript slicing required the little understood elongation factor SPT5L. These results highlight the importance of Pol V transcript slicing in RNA-mediated transcriptional gene silencing, which is a conserved process in many eukaryotes.

2018-01-29 | GSE108078 | GEO

Arabidopsis AGO3 predominantly recruits 24-nucleotide small RNAs to regulate epigenetic silencing [Bisulfite-seq]

Project description:AGO3 predominantly bound 24-nt sRNAs with 5â terminal adenine. The spectrum of AGO3-associated sRNAs was different from those bound to AGO2. By contrast, approximately 30% of AGO3-bound 24-nt sRNAs overlapped with those bound to AGO4 and over 60% of AGO3-associated 24-nt sRNA enriched loci were identical to those of AGO4. In addition, expression of AGO3 driven by AGO4 native promoter partially complemented AGO4 function and rescued DNA methylation defect in ago4-1 background. Examination of DNA methylation using bisulfite conversion of unmethylated cytosines in three genetic backgrounds of Arabidopsis thaliana.

2016-05-31 | E-GEOD-78089 | biostudies-arrayexpress

Arabidopsis AGO3 predominantly recruits 24-nucleotide small RNAs to regulate epigenetic silencing [Bisulfite-seq]

Project description:AGO3 predominantly bound 24-nt sRNAs with 5’ terminal adenine. The spectrum of AGO3-associated sRNAs was different from those bound to AGO2. By contrast, approximately 30% of AGO3-bound 24-nt sRNAs overlapped with those bound to AGO4 and over 60% of AGO3-associated 24-nt sRNA enriched loci were identical to those of AGO4. In addition, expression of AGO3 driven by AGO4 native promoter partially complemented AGO4 function and rescued DNA methylation defect in ago4-1 background.

2016-05-31 | GSE78089 | GEO

Arabidopsis AGO3 predominantly recruits 24-nucleotide small RNAs to regulate epigenetic silencing [miRNA-seq]

2016-05-31 | GSE78088 | GEO

Arabidopsis AGO3 predominantly recruits 24-nucleotide small RNAs to regulate epigenetic silencing [miRNA-seq]

Project description:AGO3 predominantly bound 24-nt sRNAs with 5â?? terminal adenine. The spectrum of AGO3-associated sRNAs was different from those bound to AGO2. By contrast, approximately 30% of AGO3-bound 24-nt sRNAs overlapped with those bound to AGO4 and over 60% of AGO3-associated 24-nt sRNA enriched loci were identical to those of AGO4. In addition, expression of AGO3 driven by AGO4 native promoter partially complemented AGO4 function and rescued DNA methylation defect in ago4-1 background. Examination of AGO3 and AGO2 bound small RNAs with/without salt stress.

2016-05-31 | E-GEOD-78088 | biostudies-arrayexpress

AGO6 functions in RNA-mediated transcriptional gene silencing in shoot and root meristems in Arabidopsis thaliana

Project description:RNA-directed DNA methylation (RdDM) is a small interfering RNA (siRNA)-mediated epigenetic modification that contributes to transposon silencing in plants. RdDM requires a complex transcriptional machinery that includes specialized RNA polymerases, named Pol IV and Pol V, as well as chromatin remodelling proteins, transcription factors, RNA binding proteins, and other plant-specific proteins whose functions are not yet clarified. In Arabidopsis thaliana, DICER-LIKE3 and members of the ARGONAUTE4 group of AROGONAUTE (AGO) proteins are involved, respectively, in generating and using 24-nt siRNAs that trigger methylation and transcriptional gene silencing (TGS) of homologous promoter sequences. AGO proteins act in silencing effector complexes by anchoring the 3â and 5â ends of the guide siRNAs at their N-terminal PAZ domain and MID domain, respectively. In addition, many AGO proteins cleave complementary target RNAs through an endonuclease (âslicerâ) activity in their C-terminal PIWI domain. AGO4 is the main AGO protein implicated in the RdDM pathway. Here we report the identification of the related AGO6 in a forward genetic screen for mutants defective in RdDM and TGS in shoot and root apical meristems in Arabidopsis thaliana. The identification of AGO6, and not AGO4, in our screen is consistent with the primary expression of AGO6 in shoot and root growing points and the preferential association of Pol V with AGO6. Examination of siRNA abundance in the trasngenic wild type plant (contains trigger and silencer transgenes) and the ago6-4 mutant.

2011-12-01 | E-GEOD-28537 | biostudies-arrayexpress

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