51
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Fei Y, Nyikó T, Molnar A. Non-perfectly matching small RNAs can induce stable and heritable epigenetic modifications and can be used as molecular markers to trace the origin and fate of silencing RNAs. Nucleic Acids Res 2021; 49:1900-1913. [PMID: 33524108 PMCID: PMC7913690 DOI: 10.1093/nar/gkab023] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 01/04/2021] [Accepted: 01/08/2021] [Indexed: 02/06/2023] Open
Abstract
Short non-coding RNA molecules (sRNAs) play a fundamental role in gene regulation and development in higher organisms. They act as molecular postcodes and guide AGO proteins to target nucleic acids. In plants, sRNA-targeted mRNAs are degraded, reducing gene expression. In contrast, sRNA-targeted DNA sequences undergo cytosine methylation referred to as RNA-directed DNA methylation (RdDM). Cytosine methylation can suppress transcription, thus sRNAs are potent regulators of gene expression. sRNA-mediated RdDM is involved in genome stability through transposon silencing, mobile signalling for epigenetic gene control and hybrid vigour. Since cytosine methylation can be passed on to subsequent generations, RdDM contributes to transgenerational inheritance of the epigenome. Using a novel approach, which can differentiate between primary (inducer) and secondary (amplified) sRNAs, we show that initiation of heritable RdDM does not require complete sequence complementarity between the sRNAs and their nuclear target sequences. sRNAs with up to four regularly interspaced mismatches are potent inducers of RdDM, however, the number and disruptive nature of nucleotide polymorphisms negatively correlate with their efficacy. Our findings contribute to understanding how sRNA can directly shape the epigenome and may be used in designing the next generation of RNA silencing constructs.
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Affiliation(s)
- Yue Fei
- University of Edinburgh, Institute of Molecular Plant Sciences, Max Born Crescent, Edinburgh EH9 3BF, UK
| | - Tünde Nyikó
- Agricultural Biotechnology Institute, Szent-Györgyi A. 4., Gödöllő 2100, Hungary
| | - Attila Molnar
- University of Edinburgh, Institute of Molecular Plant Sciences, Max Born Crescent, Edinburgh EH9 3BF, UK
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52
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Mishra V. A Comprehensive Guide to the Commercial Baculovirus Expression Vector Systems for Recombinant Protein Production. Protein Pept Lett 2020; 27:529-537. [PMID: 31721691 DOI: 10.2174/0929866526666191112152646] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 10/24/2019] [Accepted: 10/25/2019] [Indexed: 12/17/2022]
Abstract
The Baculovirus Expression Vector System (BEVS) is a workhorse for recombinant protein expression for over thirty-five years. Ever since it was first used to overexpress the human IFN-β protein, the system has been engineered and modified several times for quick and easy expression and scale-up of the recombinant proteins. Multiple gene assemblies performed on the baculovirus genome using synthetic biology methods lead to optimized overexpression of the multiprotein complexes. Nowadays, several commercially available BEVS platforms offer a variety of customizable features, and often it is confusing which one to choose for a novice user. This short review is intended to be a one-stop guide to the commercially available baculovirus technology for heterologous protein expression in the insect cells, which users can refer to choose from popular and desirable BEVS products or services.
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Affiliation(s)
- Vibhor Mishra
- Howard Hughes Medical Institute and Department of Biology, Indiana University, Bloomington, IN 47405, United States
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53
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Liu J, He Z. Small DNA Methylation, Big Player in Plant Abiotic Stress Responses and Memory. FRONTIERS IN PLANT SCIENCE 2020; 11:595603. [PMID: 33362826 PMCID: PMC7758401 DOI: 10.3389/fpls.2020.595603] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 11/18/2020] [Indexed: 05/12/2023]
Abstract
DNA methylation is a conserved epigenetic mark that plays important roles in maintaining genome stability and regulating gene expression. As sessile organisms, plants have evolved sophisticated regulatory systems to endure or respond to diverse adverse abiotic environmental challenges, i.e., abiotic stresses, such as extreme temperatures (cold and heat), drought and salinity. Plant stress responses are often accompanied by changes in chromatin modifications at diverse responsive loci, such as 5-methylcytosine (5mC) and N 6-methyladenine (6mA) DNA methylation. Some abiotic stress responses are memorized for several hours or days through mitotic cell divisions and quickly reset to baseline levels after normal conditions are restored, which is referred to as somatic memory. In some cases, stress-induced chromatin marks are meiotically heritable and can impart the memory of stress exposure from parent plants to at least the next stress-free offspring generation through the mechanisms of transgenerational epigenetic inheritance, which may offer the descendants the potential to be adaptive for better fitness. In this review, we briefly summarize recent achievements regarding the establishment, maintenance and reset of DNA methylation, and highlight the diverse roles of DNA methylation in plant responses to abiotic stresses. Further, we discuss the potential role of DNA methylation in abiotic stress-induced somatic memory and transgenerational inheritance. Future research directions are proposed to develop stress-tolerant engineered crops to reduce the negative effects of abiotic stresses.
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Affiliation(s)
- Junzhong Liu
- State Key Laboratory of Conservation and Utilization of Bio-Resources in Yunnan and Center for Life Sciences, School of Life Sciences, Yunnan University, Kunming, China
| | - Zuhua He
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China
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54
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Sun F, Hu P, Wang W, Lan Y, Du L, Zhou Y, Zhou T. Rice Stripe Virus Coat Protein-Mediated Virus Resistance Is Associated With RNA Silencing in Arabidopsis. Front Microbiol 2020; 11:591619. [PMID: 33281789 PMCID: PMC7691420 DOI: 10.3389/fmicb.2020.591619] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 10/26/2020] [Indexed: 11/13/2022] Open
Abstract
Rice stripe virus (RSV) causes rice stripe disease, which is one of the most serious rice diseases in eastern Asian countries. It has been shown that overexpression of RSV coat protein (CP) in rice plants enhances resistance against virus infection. However, the detailed mechanism underlying RSV CP-mediated virus resistance remains to be determined. In this study, we show that both translatable and non-translatable RSV CP transgenic Arabidopsis plants exhibited immunity to virus infection. By using deep sequencing analysis, transgene-derived small interfering RNAs (t-siRNAs) from non-translatable CP transgenic plants and virus-derived small interfering RNAs (vsiRNAs) mapping in the CP region from RSV-infected wild-type plants showed similar sequence distribution patterns, except for a significant increase in the abundance of t-siRNA reads compared with that of CP-derived vsiRNAs. To further test the correlation of t-siRNAs with RSV immunity, we developed RSV CP transgenic Arabidopsis plants in an siRNA-deficient dcl2/3/4 mutant background, and these CP transgenic plants showed the same sensitivity to RSV infection as non-transgenic plants. Together, our data indicate that the expression of RSV CP protein from a transgene is not a prerequisite for virus resistance and RSV CP-mediated resistance is mostly associated with the RNA silencing mechanism in Arabidopsis plants.
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Affiliation(s)
- Feng Sun
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China
| | - Peng Hu
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China.,The State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, China
| | - Wei Wang
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China.,College of Plant Protection, Nanjing Agricultural University, Nanjing, China
| | - Ying Lan
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China
| | - Linlin Du
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China
| | - Yijun Zhou
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China
| | - Tong Zhou
- Jiangsu Key Laboratory for Food Quality and Safety-State Key Laboratory Cultivation Base of Ministry of Science and Technology, Institute of Plant Protection, Jiangsu Academy of Agricultural Sciences, Nanjing, China.,College of Plant Protection, Nanjing Agricultural University, Nanjing, China
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55
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Rymen B, Ferrafiat L, Blevins T. Non-coding RNA polymerases that silence transposable elements and reprogram gene expression in plants. Transcription 2020; 11:172-191. [PMID: 33180661 PMCID: PMC7714444 DOI: 10.1080/21541264.2020.1825906] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Multisubunit RNA polymerase (Pol) complexes are the core machinery for gene expression in eukaryotes. The enzymes Pol I, Pol II and Pol III transcribe distinct subsets of nuclear genes. This family of nuclear RNA polymerases expanded in terrestrial plants by the duplication of Pol II subunit genes. Two Pol II-related enzymes, Pol IV and Pol V, are highly specialized in the production of regulatory, non-coding RNAs. Pol IV and Pol V are the central players of RNA-directed DNA methylation (RdDM), an RNA interference pathway that represses transposable elements (TEs) and selected genes. Genetic and biochemical analyses of Pol IV/V subunits are now revealing how these enzymes evolved from ancestral Pol II to sustain non-coding RNA biogenesis in silent chromatin. Intriguingly, Pol IV-RdDM regulates genes that influence flowering time, reproductive development, stress responses and plant–pathogen interactions. Pol IV target genes vary among closely related taxa, indicating that these regulatory circuits are often species-specific. Data from crops like maize, rice, tomato and Brassicarapa suggest that dynamic repositioning of TEs, accompanied by Pol IV targeting to TE-proximal genes, leads to the reprogramming of plant gene expression over short evolutionary timescales.
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Affiliation(s)
- Bart Rymen
- Institut de biologie moléculaire des plantes, Université de Strasbourg , Strasbourg, France
| | - Laura Ferrafiat
- Institut de biologie moléculaire des plantes, Université de Strasbourg , Strasbourg, France
| | - Todd Blevins
- Institut de biologie moléculaire des plantes, Université de Strasbourg , Strasbourg, France
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56
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Abstract
RNA-directed DNA methylation (RdDM) is a biological process in which non-coding RNA molecules direct the addition of DNA methylation to specific DNA sequences. The RdDM pathway is unique to plants, although other mechanisms of RNA-directed chromatin modification have also been described in fungi and animals. To date, the RdDM pathway is best characterized within angiosperms (flowering plants), and particularly within the model plant Arabidopsis thaliana. However, conserved RdDM pathway components and associated small RNAs (sRNAs) have also been found in other groups of plants, such as gymnosperms and ferns. The RdDM pathway closely resembles other sRNA pathways, particularly the highly conserved RNAi pathway found in fungi, plants, and animals. Both the RdDM and RNAi pathways produce sRNAs and involve conserved Argonaute, Dicer and RNA-dependent RNA polymerase proteins. RdDM has been implicated in a number of regulatory processes in plants. The DNA methylation added by RdDM is generally associated with transcriptional repression of the genetic sequences targeted by the pathway. Since DNA methylation patterns in plants are heritable, these changes can often be stably transmitted to progeny. As a result, one prominent role of RdDM is the stable, transgenerational suppression of transposable element (TE) activity. RdDM has also been linked to pathogen defense, abiotic stress responses, and the regulation of several key developmental transitions. Although the RdDM pathway has a number of important functions, RdDM-defective mutants in Arabidopsis thaliana are viable and can reproduce, which has enabled detailed genetic studies of the pathway. However, RdDM mutants can have a range of defects in different plant species, including lethality, altered reproductive phenotypes, TE upregulation and genome instability, and increased pathogen sensitivity. Overall, RdDM is an important pathway in plants that regulates a number of processes by establishing and reinforcing specific DNA methylation patterns, which can lead to transgenerational epigenetic effects on gene expression and phenotype.
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57
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Zhang S, Wu XQ, Xie HT, Zhao SS, Wu JG. Multifaceted roles of RNA polymerase IV in plant growth and development. JOURNAL OF EXPERIMENTAL BOTANY 2020; 71:5725-5732. [PMID: 32969476 PMCID: PMC7541909 DOI: 10.1093/jxb/eraa346] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We discuss the latest findings on RNA polymerase IV (Pol IV) in plant growth and development, providing new insights and expanding on new ideas for further, more in-depth research on Pol IV.
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Affiliation(s)
- Shuai Zhang
- Vector-borne Virus Research Center, State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Province Key Laboratory of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Xiao-Qing Wu
- Vector-borne Virus Research Center, State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Province Key Laboratory of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Hui-Ting Xie
- Vector-borne Virus Research Center, State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Province Key Laboratory of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Shan-Shan Zhao
- Vector-borne Virus Research Center, State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Province Key Laboratory of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Jian-Guo Wu
- Vector-borne Virus Research Center, State Key Laboratory of Ecological Pest Control for Fujian and Taiwan Crops, Fujian Province Key Laboratory of Plant Virology, Fujian Agriculture and Forestry University, Fuzhou, China
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58
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Papareddy RK, Páldi K, Paulraj S, Kao P, Lutzmayer S, Nodine MD. Chromatin regulates expression of small RNAs to help maintain transposon methylome homeostasis in Arabidopsis. Genome Biol 2020; 21:251. [PMID: 32943088 PMCID: PMC7499886 DOI: 10.1186/s13059-020-02163-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Accepted: 09/04/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Eukaryotic genomes are partitioned into euchromatic and heterochromatic domains to regulate gene expression and other fundamental cellular processes. However, chromatin is dynamic during growth and development and must be properly re-established after its decondensation. Small interfering RNAs (siRNAs) promote heterochromatin formation, but little is known about how chromatin regulates siRNA expression. RESULTS We demonstrate that thousands of transposable elements (TEs) produce exceptionally high levels of siRNAs in Arabidopsis thaliana embryos. TEs generate siRNAs throughout embryogenesis according to two distinct patterns depending on whether they are located in euchromatic or heterochromatic regions of the genome. siRNA precursors are transcribed in embryos, and siRNAs are required to direct the re-establishment of DNA methylation on TEs from which they are derived in the new generation. Decondensed chromatin also permits the production of 24-nt siRNAs from heterochromatic TEs during post-embryogenesis, and siRNA production from bipartite-classified TEs is controlled by their chromatin states. CONCLUSIONS Decondensation of heterochromatin in response to developmental, and perhaps environmental, cues promotes the transcription and function of siRNAs in plants. Our results indicate that chromatin-mediated siRNA transcription provides a cell-autonomous homeostatic control mechanism to help reconstitute pre-existing chromatin states during growth and development including those that ensure silencing of TEs in the future germ line.
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Affiliation(s)
- Ranjith K. Papareddy
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Katalin Páldi
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Subramanian Paulraj
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Ping Kao
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Stefan Lutzmayer
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
| | - Michael D. Nodine
- Gregor Mendel Institute (GMI), Austrian Academy of Sciences, Vienna Biocenter (VBC), Dr. Bohr-Gasse 3, 1030 Vienna, Austria
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59
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Abundant expression of maternal siRNAs is a conserved feature of seed development. Proc Natl Acad Sci U S A 2020; 117:15305-15315. [PMID: 32541052 DOI: 10.1073/pnas.2001332117] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Small RNAs are abundant in plant reproductive tissues, especially 24-nucleotide (nt) small interfering RNAs (siRNAs). Most 24-nt siRNAs are dependent on RNA Pol IV and RNA-DEPENDENT RNA POLYMERASE 2 (RDR2) and establish DNA methylation at thousands of genomic loci in a process called RNA-directed DNA methylation (RdDM). In Brassica rapa, RdDM is required in the maternal sporophyte for successful seed development. Here, we demonstrate that a small number of siRNA loci account for over 90% of siRNA expression during B. rapa seed development. These loci exhibit unique characteristics with regard to their copy number and association with genomic features, but they resemble canonical 24-nt siRNA loci in their dependence on RNA Pol IV/RDR2 and role in RdDM. These loci are expressed in ovules before fertilization and in the seed coat, embryo, and endosperm following fertilization. We observed a similar pattern of 24-nt siRNA expression in diverse angiosperms despite rapid sequence evolution at siren loci. In the endosperm, siren siRNAs show a marked maternal bias, and siren expression in maternal sporophytic tissues is required for siren siRNA accumulation. Together, these results demonstrate that seed development occurs under the influence of abundant maternal siRNAs that might be transported to, and function in, filial tissues.
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60
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Small RNA Function in Plants: From Chromatin to the Next Generation. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2020; 84:133-140. [PMID: 32518093 DOI: 10.1101/sqb.2019.84.040394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Small RNA molecules can target a particular virus, gene, or transposable element (TE) with a high degree of specificity. Their ability to move from cell to cell and recognize targets in trans also allows building networks capable of regulating a large number of related targets at once. In the case of epigenetic silencing, small RNA may use the widespread distribution of TEs in eukaryotic genomes to coordinate many loci across developmental and generational time. Here, we discuss the intriguing role of plant small RNA in targeting transposons and repeats in pollen and seeds. Epigenetic reprogramming in the germline and early seed development provides a mechanism to control genome dosage, imprinted gene expression, and incompatible hybridizations via the "triploid block."
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61
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Thieffry A, Vigh ML, Bornholdt J, Ivanov M, Brodersen P, Sandelin A. Characterization of Arabidopsis thaliana Promoter Bidirectionality and Antisense RNAs by Inactivation of Nuclear RNA Decay Pathways. THE PLANT CELL 2020; 32:1845-1867. [PMID: 32213639 PMCID: PMC7268790 DOI: 10.1105/tpc.19.00815] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 02/03/2020] [Accepted: 03/20/2020] [Indexed: 05/20/2023]
Abstract
In animals, RNA polymerase II initiates transcription bidirectionally from gene promoters to produce pre-mRNAs on the forward strand and promoter upstream transcripts (PROMPTs) on the reverse strand. PROMPTs are degraded by the nuclear exosome. Previous studies based on nascent RNA approaches concluded that Arabidopsis (Arabidopsis thaliana) does not produce PROMPTs. Here, we used steady-state RNA sequencing in mutants defective in nuclear RNA decay including the exosome to reassess the existence of Arabidopsis PROMPTs. While they are rare, we identified ∼100 cases of exosome-sensitive PROMPTs in Arabidopsis. Such PROMPTs are sources of small interfering RNAs in exosome-deficient mutants, perhaps explaining why plants have evolved mechanisms to suppress PROMPTs. In addition, we found ∼200 long, unspliced and exosome-sensitive antisense RNAs that arise from transcription start sites within parts of the genome encoding 3'-untranslated regions on the sense strand. The previously characterized noncoding RNA that regulates expression of the key seed dormancy regulator, DELAY OF GERMINATION1, is a typical representative of this class of RNAs. Transcription factor genes are overrepresented among loci with exosome-sensitive antisense RNAs, suggesting a potential for widespread control of gene expression via this class of noncoding RNAs. Lastly, we assess the use of alternative promoters in Arabidopsis and compare the accuracy of existing TSS annotations.
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Affiliation(s)
- Axel Thieffry
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
- Biotech Research and Innovation Centre, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Maria Louisa Vigh
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Jette Bornholdt
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
- Biotech Research and Innovation Centre, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Maxim Ivanov
- Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Denmark
| | - Peter Brodersen
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
| | - Albin Sandelin
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen N, Denmark
- Biotech Research and Innovation Centre, University of Copenhagen, DK-2200 Copenhagen N, Denmark
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62
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Singh J, Pikaard CS. Reconstitution of siRNA Biogenesis In Vitro: Novel Reaction Mechanisms and RNA Channeling in the RNA-Directed DNA Methylation Pathway. COLD SPRING HARBOR SYMPOSIA ON QUANTITATIVE BIOLOGY 2020; 84:195-201. [PMID: 32350049 DOI: 10.1101/sqb.2019.84.039842] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Eukaryotes deploy RNA-mediated gene silencing pathways to guard their genomes against selfish genetic elements, such as transposable elements and invading viruses. In plants, RNA-directed DNA methylation (RdDM) is used to silence selfish elements at the level of transcription. This process involves 24-nt short interfering RNAs (siRNAs) and longer noncoding RNAs to which the siRNAs base-pair. Recently, we showed that 24-nt siRNA biogenesis could be recapitulated in the test tube using purified enzymes, yielding biochemical answers to numerous questions left unresolved by prior genetic and genomic studies. Interestingly, each enzyme has activities that program what happens in the next step, thus channeling the RNAs within the RdDM pathway and restricting their diversion into alternative pathways. However, a similar mechanistic understanding is lacking for other important steps of the RdDM pathway. We discuss some of the steps most in need of biochemical investigation and important questions still in need of answers.
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Affiliation(s)
- Jasleen Singh
- Department of Molecular and Cellular Biochemistry and Department of Biology, Bloomington, Indiana 47405, USA
| | - Craig S Pikaard
- Department of Molecular and Cellular Biochemistry and Department of Biology, Bloomington, Indiana 47405, USA.,Howard Hughes Medical Institute, Indiana University, Bloomington, Indiana 47405, USA
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63
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Wang Z, Butel N, Santos-González J, Borges F, Yi J, Martienssen RA, Martinez G, Köhler C. Polymerase IV Plays a Crucial Role in Pollen Development in Capsella. THE PLANT CELL 2020; 32:950-966. [PMID: 31988265 PMCID: PMC7145478 DOI: 10.1105/tpc.19.00938] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 01/13/2020] [Accepted: 01/21/2020] [Indexed: 05/04/2023]
Abstract
In Arabidopsis (Arabidopsis thaliana), DNA-dependent RNA polymerase IV (Pol IV) is required for the formation of transposable element (TE)-derived small RNA transcripts. These transcripts are processed by DICER-LIKE3 into 24-nucleotide small interfering RNAs (siRNAs) that guide RNA-directed DNA methylation. In the pollen grain, Pol IV is also required for the accumulation of 21/22-nucleotide epigenetically activated siRNAs, which likely silence TEs via post-transcriptional mechanisms. Despite this proposed role of Pol IV, its loss of function in Arabidopsis does not cause a discernible pollen defect. Here, we show that the knockout of NRPD1, encoding the largest subunit of Pol IV, in the Brassicaceae species Capsella (Capsella rubella), caused postmeiotic arrest of pollen development at the microspore stage. As in Arabidopsis, all TE-derived siRNAs were depleted in Capsella nrpd1 microspores. In the wild-type background, the same TEs produced 21/22-nucleotide and 24-nucleotide siRNAs; these processes required Pol IV activity. Arrest of Capsella nrpd1 microspores was accompanied by the deregulation of genes targeted by Pol IV-dependent siRNAs. TEs were much closer to genes in Capsella compared with Arabidopsis, perhaps explaining the essential role of Pol IV in pollen development in Capsella. Our discovery that Pol IV is functionally required in Capsella microspores emphasizes the relevance of investigating different plant models.
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Affiliation(s)
- Zhenxing Wang
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
| | - Nicolas Butel
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
| | - Juan Santos-González
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
| | - Filipe Borges
- Howard Hughes Medical Institute and Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724
| | - Jun Yi
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
| | - Robert A Martienssen
- Howard Hughes Medical Institute and Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724
| | - German Martinez
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
| | - Claudia Köhler
- Department of Plant Biology, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala 75007, Sweden
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64
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Small RNAs in the Transgenerational Inheritance of Epigenetic Information. Trends Genet 2020; 36:203-214. [DOI: 10.1016/j.tig.2019.12.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 11/19/2019] [Accepted: 12/06/2019] [Indexed: 01/21/2023]
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65
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Böhrer M, Rymen B, Himber C, Gerbaud A, Pflieger D, Laudencia-Chingcuanco D, Cartwright A, Vogel J, Sibout R, Blevins T. Integrated Genome-Scale Analysis and Northern Blot Detection of Retrotransposon siRNAs Across Plant Species. Methods Mol Biol 2020; 2166:387-411. [PMID: 32710422 DOI: 10.1007/978-1-0716-0712-1_23] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Cells have sophisticated RNA-directed mechanisms to regulate genes, destroy viruses, or silence transposable elements (TEs). In terrestrial plants, a specialized non-coding RNA machinery involving RNA polymerase IV (Pol IV) and small interfering RNAs (siRNAs) targets DNA methylation and silencing to TEs. Here, we present a bioinformatics protocol for annotating and quantifying siRNAs that derive from long terminal repeat (LTR) retrotransposons. The approach was validated using small RNA northern blot analyses, comparing the species Arabidopsis thaliana and Brachypodium distachyon. To assist hybridization probe design, we configured a genome browser to show small RNA-seq mappings in distinct colors and shades according to their nucleotide lengths and abundances, respectively. Samples from wild-type and pol IV mutant plants, cross-species negative controls, and a conserved microRNA control validated the detected siRNA signals, confirming their origin from specific TEs and their Pol IV-dependent biogenesis. Moreover, an optimized labeling method yielded probes that could detect low-abundance siRNAs from B. distachyon TEs. The integration of de novo TE annotation, small RNA-seq profiling, and northern blotting, as outlined here, will facilitate the comparative genomic analysis of RNA silencing in crop plants and non-model species.
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Affiliation(s)
- Marcel Böhrer
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France
| | - Bart Rymen
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France
| | - Christophe Himber
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France
| | - Aude Gerbaud
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France
| | - David Pflieger
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France
| | | | - Amy Cartwright
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - John Vogel
- DOE Joint Genome Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Richard Sibout
- INRAE, UR BIA, Nantes, France.,Institut Jean-Pierre Bourgin, UMR 1318, INRAE, AgroParisTech, CNRS, Université Paris-Saclay, Versailles, France
| | - Todd Blevins
- Institut de Biologie Moléculaire des Plantes, CNRS UPR2357, Université de Strasbourg, Strasbourg, France.
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Ferrafiat L, Pflieger D, Singh J, Thieme M, Böhrer M, Himber C, Gerbaud A, Bucher E, Pikaard CS, Blevins T. The NRPD1 N-terminus contains a Pol IV-specific motif that is critical for genome surveillance in Arabidopsis. Nucleic Acids Res 2019; 47:9037-9052. [PMID: 31372633 PMCID: PMC6753494 DOI: 10.1093/nar/gkz618] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Revised: 07/03/2019] [Accepted: 07/11/2019] [Indexed: 12/29/2022] Open
Abstract
RNA-guided surveillance systems constrain the activity of transposable elements (TEs) in host genomes. In plants, RNA polymerase IV (Pol IV) transcribes TEs into primary transcripts from which RDR2 synthesizes double-stranded RNA precursors for small interfering RNAs (siRNAs) that guide TE methylation and silencing. How the core subunits of Pol IV, homologs of RNA polymerase II subunits, diverged to support siRNA biogenesis in a TE-rich, repressive chromatin context is not well understood. Here we studied the N-terminus of Pol IV’s largest subunit, NRPD1. Arabidopsis lines harboring missense mutations in this N-terminus produce wild-type (WT) levels of NRPD1, which co-purifies with other Pol IV subunits and RDR2. Our in vitro transcription and genomic analyses reveal that the NRPD1 N-terminus is critical for robust Pol IV-dependent transcription, siRNA production and DNA methylation. However, residual RNA-directed DNA methylation observed in one mutant genotype indicates that Pol IV can operate uncoupled from the high siRNA levels typically observed in WT plants. This mutation disrupts a motif uniquely conserved in Pol IV, crippling the enzyme's ability to inhibit retrotransposon mobilization. We propose that the NRPD1 N-terminus motif evolved to regulate Pol IV function in genome surveillance.
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Affiliation(s)
- Laura Ferrafiat
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
| | - David Pflieger
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
| | - Jasleen Singh
- Howard Hughes Medical Institute, Indiana University, Bloomington, IN 47405, USA.,Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | - Michael Thieme
- Botanisches Institut, Universität Basel, CH-4056 Basel, Switzerland
| | - Marcel Böhrer
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
| | - Christophe Himber
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
| | - Aude Gerbaud
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
| | - Etienne Bucher
- Botanisches Institut, Universität Basel, CH-4056 Basel, Switzerland
| | - Craig S Pikaard
- Howard Hughes Medical Institute, Indiana University, Bloomington, IN 47405, USA.,Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | - Todd Blevins
- Institut de Biologie Moléculaire des Plantes, CNRS, Université de Strasbourg, F-67084 Strasbourg, France
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67
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Wendte JM, Haag JR, Pontes OM, Singh J, Metcalf S, Pikaard CS. The Pol IV largest subunit CTD quantitatively affects siRNA levels guiding RNA-directed DNA methylation. Nucleic Acids Res 2019; 47:9024-9036. [PMID: 31329950 PMCID: PMC6753486 DOI: 10.1093/nar/gkz615] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Revised: 06/29/2019] [Accepted: 07/05/2019] [Indexed: 11/27/2022] Open
Abstract
In plants, nuclear multisubunit RNA polymerases IV and V are RNA Polymerase II-related enzymes that synthesize non-coding RNAs for RNA-directed DNA methylation (RdDM) and transcriptional gene silencing. Here, we tested the importance of the C-terminal domain (CTD) of Pol IV’s largest subunit given that the Pol II CTD mediates multiple aspects of Pol II transcription. We show that the CTD is dispensable for Pol IV catalytic activity and Pol IV termination-dependent activation of RNA-DEPENDENT RNA POLYMERASE 2, which partners with Pol IV to generate dsRNA precursors of the 24 nt siRNAs that guide RdDM. However, 24 nt siRNA levels decrease ∼80% when the CTD is deleted. RNA-dependent cytosine methylation is also reduced, but only ∼20%, suggesting that siRNA levels typically exceed the levels needed for methylation of most loci. Pol IV-dependent loci affected by loss of the CTD are primarily located in chromosome arms, similar to loci dependent CLSY1/2 or SHH1, which are proteins implicated in Pol IV recruitment. However, deletion of the CTD does not phenocopy clsy or shh1 mutants, consistent with the CTD affecting post-recruitment aspects of Pol IV activity at target loci.
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Affiliation(s)
- Jered M Wendte
- Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA
| | - Jeremy R Haag
- Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA.,Division of Biology and Biomedical Sciences, Washington University, St Louis, MO 63130, USA
| | - Olga M Pontes
- Division of Biology and Biomedical Sciences, Washington University, St Louis, MO 63130, USA
| | - Jasleen Singh
- Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA
| | - Sara Metcalf
- Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA
| | - Craig S Pikaard
- Department of Biology, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA.,Department of Molecular and Cellular Biochemistry, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA.,Howard Hughes Medical Institute, Indiana University, 915 E. Third Street, Bloomington, IN 47405, USA
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