Multisubunit RNA Polymerases IV and V: Purveyors of Non-Coding RNA for Plant Gene Silencing
01 Aug 2011-Nature Reviews Molecular Cell Biology (Nature Publishing Group)-Vol. 12, Iss: 8, pp 483-492
TL;DR: Plants have evolved two additional multisubunit RNA polymerases,RNA polymerases IV and V, which orchestrate non-coding RNA-mediated gene silencing processes affecting development, transposon taming, antiviral defence and allelic crosstalk, and provides the unique opportunity to study the functional diversification of a eukaryotic RNA polymerase family.
Abstract: In all eukaryotes, nuclear DNA-dependent RNA polymerases I, II and III synthesize the myriad RNAs that are essential for life. Remarkably, plants have evolved two additional multisubunit RNA polymerases, RNA polymerases IV and V, which orchestrate non-coding RNA-mediated gene silencing processes affecting development, transposon taming, antiviral defence and allelic crosstalk. Biochemical details concerning the templates and products of RNA polymerases IV and V are lacking. However, their subunit compositions reveal that they evolved as specialized forms of RNA polymerase II, which provides the unique opportunity to study the functional diversification of a eukaryotic RNA polymerase family.
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TL;DR: Although the inheritance of epigenetic characters can certainly occur-particularly in plants-how much is due to the environment and the extent to which it happens in humans remain unclear.
1,291 citations
Cites background from "Multisubunit RNA Polymerases IV and..."
...In Arabidopsis, genes required for RdDM encode factors associated with the large subunits of RNA polymerases PolIV and PolV, which are closely related to PolII (Eun et al., 2012; Haag and Pikaard, 2011; Law and Jacobsen, 2010)....
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...For example, RNA-dependent RNA polymerase 2 is required for 24 nt siRNA biogenesis and is associated with PolIV, whereas Argonaute proteins that bind 24 nt siRNA are associated with PolV, as are chromatin remodelers, histone methyltransferases, and DNA-binding proteins, suggesting a link with chromatin as well as RNAi (Haag and Pikaard, 2011; Law and Jacobsen, 2010)....
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...…biogenesis and is associated with PolIV, whereas Argonaute proteins that bind 24 nt siRNA are associated with PolV, as are chromatin remodelers, histone methyltransferases, and DNA-binding proteins, suggesting a link with chromatin as well as RNAi (Haag and Pikaard, 2011; Law and Jacobsen, 2010)....
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TL;DR: RNA-directed DNA methylation, the major small RNA-mediated epigenetic pathway in plants, is implicated in pathogen defence, stress responses and reproduction, as well as in interallelic and intercellular communication.
Abstract: RNA-directed DNA methylation (RdDM) is the major small RNA-mediated epigenetic pathway in plants. RdDM requires a specialized transcriptional machinery that comprises two plant-specific RNA polymerases - Pol IV and Pol V - and a growing number of accessory proteins, the functions of which in the RdDM mechanism are only partially understood. Recent work has revealed variations in the canonical RdDM pathway and identified factors that recruit Pol IV and Pol V to specific target sequences. RdDM, which transcriptionally represses a subset of transposons and genes, is implicated in pathogen defence, stress responses and reproduction, as well as in interallelic and intercellular communication.
1,171 citations
TL;DR: A growing number of functions are emerging for RNA interference in the nucleus, in addition to well-characterized roles in post-transcriptional gene silencing in the cytoplasm, and increasing evidence indicates that RNAi regulates transcription through interaction with transcriptional machinery.
Abstract: A growing number of functions are emerging for RNA interference (RNAi) in the nucleus, in addition to well-characterized roles in post-transcriptional gene silencing in the cytoplasm. Epigenetic modifications directed by small RNAs have been shown to cause transcriptional repression in plants, fungi and animals. Additionally, increasing evidence indicates that RNAi regulates transcription through interaction with transcriptional machinery. Nuclear small RNAs include small interfering RNAs (siRNAs) and PIWI-interacting RNAs (piRNAs) and are implicated in nuclear processes such as transposon regulation, heterochromatin formation, developmental gene regulation and genome stability.
882 citations
TL;DR: It is shown that most asymmetric methylation is facilitated byDDM1 and mediated by the methyltransferase CMT2 separately from RdDM, and that heterochromatic sequences preferentially require DDM1 for DNA methylation and that this preference depends on linker histone H1.
880 citations
Cites background from "Multisubunit RNA Polymerases IV and..."
...DRD1 is associated with RNA polymerase V, a derivative of RNA polymerase II that shares most Pol II subunits (Haag and Pikaard, 2011)....
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...This conundrum is exemplified by the RdDM pathway, which silences TE expression yet requires TE transcripts to function (Haag and Pikaard, 2011)....
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...RNA Pol V and associated factors are believed to produce nascent transcripts from target loci that are recognized by sRNA-containing AGO4 complexes that target DNA methylation via DRM enzymes (Haag and Pikaard, 2011)....
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TL;DR: The biogenesis of plant small RNAs, such as microRNAs, secondary siRNAs and heterochromatic siRNas, and their diverse cellular and developmental functions, including in reproductive transitions, genomic imprinting and paramutation are discussed.
Abstract: Plant genomes encode various small RNAs that function in distinct, yet overlapping, genetic and epigenetic silencing pathways. However, the abundance and diversity of small-RNA classes varies among plant species, suggesting coevolution between environmental adaptations and gene-silencing mechanisms. Biogenesis of small RNAs in plants is well understood, but we are just beginning to uncover their intricate regulation and activity. Here, we discuss the biogenesis of plant small RNAs, such as microRNAs, secondary siRNAs and heterochromatic siRNAs, and their diverse cellular and developmental functions, including in reproductive transitions, genomic imprinting and paramutation. We also discuss the diversification of small-RNA-directed silencing pathways through the expansion of RNA-dependent RNA polymerases, DICER proteins and ARGONAUTE proteins.
752 citations
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