Genome-wide identification of non-coding RNAs targeted by XRN exoribonucleases in collaboration with FRY1 using RNA-Seq in Arabidopsis thaliana.
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ABSTRACT: We report new insight of non-coding RNA degradation mediated by XRN exoribonucleases and FRY1 in Arabidopsis thaliana. We suggest that XRN3, in combination with FRY1, is required to prevent the accumulation of 3’ extensions that arise from thousands of mRNA and miRNA precursor transcripts.
Project description:We report new insight of non-coding RNA degradation mediated by XRN exoribonucleases and FRY1 in Arabidopsis thaliana. We suggest that XRN3, in combination with FRY1, is required to prevent the accumulation of 3’ extensions that arise from thousands of mRNA and miRNA precursor transcripts. Examination of genome-wide transcriptomes of Arabidopsis genotypes such as fry1-6, xrn3-3, xrn2-1xrn3-3, xrn2-1xrn4-6 and xrn3-3xrn4-6 using directional RNA-Seq method.
Project description:XRN 5′-3′ exoribonucleases play crucial roles in the control of RNA processing, quality, and quantity in eukaryotes. Although genome-wide profiling of RNA decay fragments is now feasible, how XRNs shape the plant mRNA degradome remains elusive. Here, we profiled and analyzed the RNA degradomes of the Arabidopsis wild type and mutants with defects in XRN activity. Deficiency of nuclear XRN3 or cytoplasmic XRN4 but not nuclear XRN2 activity largely altered Arabidopsis mRNA decay profiles. In addition to the primary XRN4 substrates derived from decapping and microRNA-directed slicing, terminating ribosome- and exon junction complex-protected fragments produced from XRN4-mediated cytoplasmic decay also represent the most abundant decay intermediates of Arabidopsis mRNAs. Short excised linear introns and cleaved pre-mRNA fragments downstream of polyadenylation sites were polyadenylated and stabilized in the xrn3 mutant, demonstrating the function of XRN3 in the removal of cleavage remnants from pre-mRNA processing. Further analysis of stabilized XRN3 substrates confirmed that polyadenylation cleavage frequently occurs after an adenosine. An increase in decay intermediates with 5′ ends upstream of a consensus motif in the xrn4 mutant suggests an endonucleolytic cleavage mechanism targeting the 3′ untranslated region of many Arabidopsis mRNAs. However, analysis of decay fragments stabilized in the xrn4 mutant indicated that, except for microRNA-directed slicing, endonucleolytic cleavage events in the coding sequence might rarely result in major decay intermediates. Together, the results of this study reveal major substrates and products of nuclear and cytoplasmic XRNs along Arabidopsis transcripts and provide a basis for precise interpretation of RNA degradome data.
Project description:The XRN family of 5'→3' exoribonucleases is critical for ensuring the fidelity of cellular RNA turnover in eukaryotes. Highly conserved across species, the family is typically represented by one cytoplasmic enzyme (XRN1/PACMAN or XRN4) and one or more nuclear enzymes (XRN2/RAT1 and XRN3). Cytoplasmic and/or nuclear XRNs have proven to be essential in all organisms tested, and deficiencies can have severe developmental phenotypes, demonstrating that XRNs are indispensable in fungi, plants and animals. XRNs degrade diverse RNA substrates during general RNA decay and function in specialized processes integral to RNA metabolism, such as nonsense-mediated decay (NMD), gene silencing, rRNA maturation, and transcription termination. Here, we review current knowledge of XRNs, highlighting recent work of high impact and future potential. One example is the breakthrough in our understanding of how XRN1 processively degrades 5' monophosphorylated RNA, revealed by its crystal structure and mutational analysis. The expanding knowledge of XRN substrates and interacting partners is outlined and the functions of XRNs are interpreted at the organismal level using available mutant phenotypes. Finally, three case studies are discussed in more detail to underscore a few of the most exciting areas of research on XRN function: XRN4 involvement in small RNA-associated processes in plants, the roles of XRN1/PACMAN in Drosophila development, and the function of human XRN2 in nuclear transcriptional quality control. This article is part of a Special Issue entitled: RNA Decay mechanisms.
Project description:In Arabidopsis thaliana two nuclear 5'-3' exonucleases, XRN2 & 3, are involved in the degradation and processing of several classes of nuclear RNAs and in transcription termination of RNA polymerase II. The role of XRN3 in Pol II transcription termination is investigated by combining two different types of RNA-seq data for Col-0 background WT and xrn3-8 mutant A. thaliana seedlings. The data for the experiment comprises single molecule Direct RNA Sequencing of unamplified RNA (3x WT, 4x xrn3-8 mutant) and high-depth Illumina strand-specific short read sequencing of PCR amplified ribosomal-RNA depleted RNA (Illumina TruSeq stranded ribozero Plant kit, 3x WT, 3x xrm3-8 mutant). In the xrn3 mutant, these data reveal a widespread accumulation of non-coding intergenic transcripts (xrn3-associated transcripts - XATs) generated by Pol II read-through transcription that are usually polyadenylated and lack the 5' cap structure. This data highlights the important role of exoribonucleases in the torpedo mechanism of Pol II transcription termination and show that a global disturbance in this process significantly impacts both gene expression and transcriptome integrity.
Project description:In Arabidopsis thaliana two nuclear 5'-3' exonucleases, XRN2 & 3, are involved in the degradation and processing of several classes of nuclear RNAs and in transcription termination of RNA polymerase II. The role of XRN3 in Pol II transcription termination is investigated by combining two different types of RNA-seq data for Col-0 background WT and xrn3-8 mutant A. thaliana seedlings. The data for the experiment comprises single molecule Direct RNA Sequencing of unamplified RNA (3x WT, 4x xrn3-8 mutant) and high-depth Illumina strand-specific short read sequencing of PCR amplified ribosomal-RNA depleted RNA (Illumina TruSeq stranded ribozero Plant kit, 3x WT, 3x xrm3-8 mutant). In the xrn3 mutant, these data reveal a widespread accumulation of non-coding intergenic transcripts (xrn3-associated transcripts - XATs) generated by Pol II read-through transcription that are usually polyadenylated and lack the 5' cap structure. This data highlights the important role of exoribonucleases in the torpedo mechanism of Pol II transcription termination and show that a global disturbance in this process significantly impacts both gene expression and transcriptome integrity.
Project description:Abstract: In plants, the molecular function(s) of the nuclear localised 5’-3’ EXORIBONUCLEASES (XRNs) are unclear, however their activity is reported to have a significant effect on gene expression and SAL1-mediated retrograde signaling. Using Parallel Analysis of RNA Ends (PARE) we document a dramatic increase in uncapped RNA substrates of the XRNs in both sal1 and xrn2xrn3 mutants. We find that a major consequence of reducing SAL1 or XRN activity is RNA Polymerase II (Pol II) 3’ read-through. This occurs at 72% of expressed genes, demonstrating a major genome-wide role for the XRN-torpedo model of transcription termination in Arabidopsis. Read-through is speculated to have a negative effect on transcript abundance, however we do not observe this. Rather, we identify a strong association between read-though and increased transcript abundance of tandemly orientated downstream genes, strongly correlated with the proximity (<1,000bp) and expression of the upstream gene. We observe read-though in the proximity of 903 genes upregulated in the sal1-8 retrograde signaling mutant; thus, this phenomenon may directly account for up to 23% of genes upregulated in sal1-8. Using APX2 and AT5G43770 as exemplars, we genetically uncouple read-through loci from downstream genes to validate the principle of read-through mediated mRNA regulation, potentially providing one mechanism by which an obstensibly post-transcriptional exoribonuclease that targets uncapped RNAs could modulate gene expression.
Project description:The transition between exponential and stationary phase is a natural phenomenon for all bacteria and requires a massive readjustment of the bacterial transcriptome. Exoribonucleases are key enzymes in the transition between the two growth phases. PNPase, RNase R and RNase II are the major degradative exoribonucleases in Escherichia coli. We analysed the whole transcriptome of exponential and stationary phases from the WT and mutants lacking these exoribonucleases (Δpnp, Δrnr, Δrnb, and ΔrnbΔrnr). When comparing the cells from exponential phase with the cells from stationary phase more than 1000 transcripts were differentially expressed, but only 491 core transcripts were common to all strains. There were some differences in the number and transcripts affected depending on the strain, suggesting that exoribonucleases influence the transition between these two growth phases differently. Interestingly, we found that the double mutant RNase II/RNase R is similar to the RNase R single mutant in exponential phase while in stationary phase it seems to be closer to the RNase II single mutant. This is the first global transcriptomic work comparing the roles of exoribonucleases in the transition between exponential and stationary phase.
Project description:The LSM2-8 complex specifically targets nuclear RNAs generated from loci bearing histone H3K27me3 for degradation through the exonuclease XRN-2 In fission yeast and plants RNA-processing pathways including co-transcriptional degradation of nuclear mRNAs contributes to heterochromatic gene silencing additionally to the well-known transcriptional repression, but it was not knownunclear if this extra level of regulation also to occur in metazoans. Here we report the discovery of a related pathway in somatic cells of the flatworm C. elegans. The highly conserved, RNA binding LSM2-8 complex is shown to silence selectively heterochromatic reporters and endogenous genes bearing the Polycomb mark H2K27me3. LSM2-8-mediated silencing is independent of H3K9me2/me3 but depends on mes-2, the Polycomb-like histone methyl transferase. LSM2-8-mediated silencing is detectable from early embryonic stages through adulthood. The LSM2-8 complex works cooperatively with XRN-2, a 5’-3’ exonuclease, and disruption of the pathway leads to stabilized targeted mRNAs. Developmental defects and premature death were observed in worms lacking LSM-8, and levels of H3K27me3 dropped slightly at Pc-targeted loci. LSM2-8-mediated silencing of H3K27me3-bound regions defines a new mechanism of selective heterochromatin gene silencing not previously shown for higher eukaryotes.
Project description:The LSM2-8 complex specifically targets nuclear RNAs generated from loci bearing histone H3K27me3 for degradation through the exonuclease XRN-2 In fission yeast and plants RNA-processing pathways including co-transcriptional degradation of nuclear mRNAs contributes to heterochromatic gene silencing additionally to the well-known transcriptional repression, but it was not knownunclear if this extra level of regulation also to occur in metazoans. Here we report the discovery of a related pathway in somatic cells of the flatworm C. elegans. The highly conserved, RNA binding LSM2-8 complex is shown to silence selectively heterochromatic reporters and endogenous genes bearing the Polycomb mark H2K27me3. LSM2-8-mediated silencing is independent of H3K9me2/me3 but depends on mes-2, the Polycomb-like histone methyl transferase. LSM2-8-mediated silencing is detectable from early embryonic stages through adulthood. The LSM2-8 complex works cooperatively with XRN-2, a 5’-3’ exonuclease, and disruption of the pathway leads to stabilized targeted mRNAs. Developmental defects and premature death were observed in worms lacking LSM-8, and levels of H3K27me3 dropped slightly at Pc-targeted loci. LSM2-8-mediated silencing of H3K27me3-bound regions defines a new mechanism of selective heterochromatin gene silencing not previously shown for higher eukaryotes.