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Lukhovitskaya N, Brown K, Hua L, Pate AE, Carr JP, Firth AE. A novel ilarvirus protein CP-RT is expressed via stop codon readthrough and suppresses RDR6-dependent RNA silencing. PLoS Pathog 2024; 20:e1012034. [PMID: 38814986 PMCID: PMC11166343 DOI: 10.1371/journal.ppat.1012034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 06/11/2024] [Accepted: 05/03/2024] [Indexed: 06/01/2024] Open
Abstract
Ilarviruses are a relatively understudied but important group of plant RNA viruses that includes a number of crop pathogens. Their genomes comprise three RNA segments encoding two replicase subunits, movement protein, coat protein (CP), and (in some ilarvirus subgroups) a protein that suppresses RNA silencing. Here we report that, in many ilarviruses, RNA3 encodes an additional protein (termed CP-RT) as a result of ribosomal readthrough of the CP stop codon into a short downstream readthrough (RT) ORF. Using asparagus virus 2 as a model, we find that CP-RT is expressed in planta where it functions as a weak suppressor of RNA silencing. CP-RT expression is essential for persistent systemic infection in leaves and shoot apical meristem. CP-RT function is dependent on a putative zinc-finger motif within RT. Replacing the asparagus virus 2 RT with the RT of an ilarvirus from a different subgroup restored the ability to establish persistent infection. These findings open up a new avenue for research on ilarvirus silencing suppression, persistent meristem invasion and vertical transmission.
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Affiliation(s)
- Nina Lukhovitskaya
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Katherine Brown
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
| | - Lei Hua
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Adrienne E. Pate
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - John P. Carr
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Andrew E. Firth
- Department of Pathology, University of Cambridge, Cambridge, United Kingdom
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2
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Palukaitis P, Yoon JY. Defense signaling pathways in resistance to plant viruses: Crosstalk and finger pointing. Adv Virus Res 2024; 118:77-212. [PMID: 38461031 DOI: 10.1016/bs.aivir.2024.01.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/11/2024]
Abstract
Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.
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Affiliation(s)
- Peter Palukaitis
- Graduate School of Plant Protection and Quarantine, Jeonbuk National University, Jeonju, Jeollabuk-do, Republic of Korea.
| | - Ju-Yeon Yoon
- Graduate School of Plant Protection and Quarantine, Jeonbuk National University, Jeonju, Jeollabuk-do, Republic of Korea.
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3
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Ebrahimi S, Eini O, Baßler A, Hanke A, Yildirim Z, Wassenegger M, Krczal G, Uslu VV. Beet Curly Top Iran Virus Rep and V2 Suppress Post-Transcriptional Gene Silencing via Distinct Modes of Action. Viruses 2023; 15:1996. [PMID: 37896771 PMCID: PMC10611197 DOI: 10.3390/v15101996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 09/21/2023] [Accepted: 09/23/2023] [Indexed: 10/29/2023] Open
Abstract
Beet curly top Iran virus (BCTIV) is a yield-limiting geminivirus belonging to the becurtovirus genus. The genome organization of BCTIV is unique such that the complementary strand of BCTIV resembles Mastrevirus, whereas the virion strand organization is similar to the Curtovirus genus. Geminiviruses are known to avoid the plant defense system by suppressing the RNA interference mechanisms both at the transcriptional gene silencing (TGS) and post-transcriptional gene silencing (PTGS) levels. Multiple geminivirus genes have been identified as viral suppressors of RNA silencing (VSR) but VSR activity remains mostly elusive in becurtoviruses. We found that BCTIV-V2 and -Rep could suppress specific Sense-PTGS mechanisms with distinct efficiencies depending on the nature of the silencing inducer and the target gene. Local silencing induced by GFP inverted repeat (IR) could not be suppressed by V2 but was partially reduced by Rep. Accordingly, we documented that Rep but not V2 could suppress systemic silencing induced by GFP-IR. In addition, we showed that the VSR activity of Rep was partly regulated by RNA-dependent RNA Polymerase 6 (RDR6), whereas the VSR activity of V2 was independent of RDR6. Domain mapping for Rep showed that an intact Rep protein was required for the suppression of PTGS. In summary, we showed that BCTIV-Rep and -V2 function as silencing suppressors with distinct modes of action.
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Affiliation(s)
- Saeideh Ebrahimi
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
- Department of Plant Protection, University of Zanjan, Zanjan 313, Iran
| | - Omid Eini
- Department of Plant Protection, University of Zanjan, Zanjan 313, Iran
- Department of Phytopathology, Institute for Sugar Beet Research, 37079 Göttingen, Germany
| | - Alexandra Baßler
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
| | - Arvid Hanke
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
- MAPS, COS, Heidelberg University, 69120 Heidelberg, Germany
| | - Zeynep Yildirim
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
| | - Michael Wassenegger
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
| | - Gabi Krczal
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
| | - Veli Vural Uslu
- RLP AgroScience GmbH, Breitenweg 71, 67435 Neustadt an der Weinstraße, Germany
- MAPS, COS, Heidelberg University, 69120 Heidelberg, Germany
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4
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Isogai M, Yoshikoshi M, Seki K, Masuko-Suzuki H, Watanabe M, Matsuo K, Yaegashi H. Seed transmission of raspberry bushy dwarf virus is blocked in Nicotiana benthamiana plants by preventing virus entry into the embryo from the infected embryo sac and endosperm. Arch Virol 2023; 168:138. [PMID: 37046148 DOI: 10.1007/s00705-023-05767-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2023] [Accepted: 03/21/2023] [Indexed: 04/14/2023]
Abstract
Raspberry bushy dwarf virus (RBDV) is transmitted through seed in infected red raspberry plants after pollination with pollen grains from healthy red raspberry plants. Here, we show that RBDV is not transmitted through seeds in infected Nicotiana benthamiana (Nb) plants after pollination with virus-free Nb pollen grains. Chromogenic in situ hybridization revealed that the virus invades the shoot apical meristem and the ovule, including the embryo sac, of RBDV-infected Nb plants; however, in seeds that developed from infected embryo sacs after fertilization by virus-free sperm cells, RBDV was absent in the embryos and present in the endosperms. When we analyzed seed transmission of RBDV in Nb mutants with mutations in dicer-like enzyme 2 and 4 (NbDCL2&4) or RNA-dependent RNA polymerase 6 (NbRDR6), RBDV was not present in the offspring from seeds with embryos and endosperms that did not express NbDCL2&4 or NbRDR6. These results suggest that seed transmission of RBDV is prevented by evasion of infection by the embryo and that RNA silencing is not essential for preventing seed transmission of RBDV in Nb plants.
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Affiliation(s)
- Masamichi Isogai
- Plant Pathology Laboratory, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, 020-8550, Japan.
| | - Mizuna Yoshikoshi
- Plant Pathology Laboratory, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, 020-8550, Japan
| | - Kentaro Seki
- Plant Pathology Laboratory, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, 020-8550, Japan
| | - Hiromi Masuko-Suzuki
- Graduate School of Life Sciences, Tohoku University, 1-1, Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan
| | - Masao Watanabe
- Graduate School of Life Sciences, Tohoku University, 1-1, Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan
| | - Kouki Matsuo
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology, 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, 062-8517, Japan
| | - Hajime Yaegashi
- Plant Pathology Laboratory, Faculty of Agriculture, Iwate University, 18-8, Ueda 3-chome, Morioka, 020-8550, Japan
- Agri-Inovation Center, Iwate University, 18-8, Ueda 3-chome, 020-8550, Morioka, Japan
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5
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Kumar R, Dasgupta I. Geminiviral C4/AC4 proteins: An emerging component of the viral arsenal against plant defence. Virology 2023; 579:156-168. [PMID: 36693289 DOI: 10.1016/j.virol.2023.01.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 12/26/2022] [Accepted: 01/08/2023] [Indexed: 01/12/2023]
Abstract
Virus infection triggers a plethora of defence reactions in plants to incapacitate the intruder. Viruses, in turn, have added additional functions to their genes so that they acquire capabilities to neutralize the above defence reactions. In plant-infecting viruses, the family Geminiviridae comprises members, majority of whom encode 6-8 genes in their small single-stranded DNA genomes. Of the above genes, one which shows the most variability in its amino acid sequence is the C4/AC4. Recent studies have uncovered evidence, which point towards a wide repertoire of functions performed by C4/AC4 revealing its role as a major player in suppressing plant defence. This review summarizes the various plant defence mechanisms against viruses and highlights how C4/AC4 has evolved to counter most of them.
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Affiliation(s)
- Rohit Kumar
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India
| | - Indranil Dasgupta
- Department of Plant Molecular Biology, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
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6
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Pei J, Feng T, Long H, Chen Y, Pei Y, Sun Y. Molecular Characterization and Virus-Induced Gene Silencing of a Collagen Gene, Me-col-1, in Root-Knot Nematode Meloidogyne enterolobii. LIFE (BASEL, SWITZERLAND) 2022; 12:life12122103. [PMID: 36556467 PMCID: PMC9784238 DOI: 10.3390/life12122103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 12/09/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022]
Abstract
Meloidogyne enterolobii, a highly pathogenic root-knot nematode species, causes serious damage to agricultural production worldwide. Collagen is an important part of the nematode epidermis, which is crucial for nematode shape maintenance, motility, and reproduction. In this study, we report that a novel collagen gene, Me-col-1, from the highly pathogenic root-knot nematode species Meloidogyne enterolobi was required for the egg formation of this pathogen. Me-col-1 encodes a protein with the size of 35 kDa, which is closely related to collagen found in other nematodes. Real-time PCR assays showed that the expression of Me-col-1 was highest in eggs and lowest in pre-parasitic second-stage juveniles (preJ2). Interestingly, knockdown of Me-col-1 did not compromise the survival rate of preJ2 but significantly reduced the egg production and consequentially caused 35.79% lower multiplication rate (Pf/Pi) compared with control. Our study provides valuable information for better understanding the function of collagen genes in the nematode life cycle, which can be used in the development of effective approaches for nematode control.
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Affiliation(s)
- Ji Pei
- College of Plant Protection/Key Laboratory of Green Prevention and Control of Tropical Plant Diseases and Pests, Ministry of Education, Hainan University, Haikou 570228, China
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
| | - Tuizi Feng
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
| | - Haibo Long
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
- Correspondence:
| | - Yuan Chen
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
| | - Yueling Pei
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
| | - Yanfang Sun
- Key Laboratory of Integrated Pest Management on Tropical Crops, Ministry of Agriculture and Rural Affairs, Institute of Environment and Plant Protection, Chinese Academy of Tropical Agricultural Sciences, Haikou 571101, China
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Comprehensive In Silico Analysis of RNA Silencing-Related Genes and Their Regulatory Elements in Wheat (Triticum aestivum L.). BIOMED RESEARCH INTERNATIONAL 2022; 2022:4955209. [PMID: 36177060 PMCID: PMC9513535 DOI: 10.1155/2022/4955209] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 08/09/2022] [Accepted: 08/13/2022] [Indexed: 11/17/2022]
Abstract
Dicer-like (DCL), Argonaute (AGO), and RNA-dependent RNA polymerase (RDR) are known as the three major gene families that act as the critical components of RNA interference or silencing mechanisms through the noncoding small RNA molecules (miRNA and siRNA) to regulate the expressions of protein-coding genes in eukaryotic organisms. However, most of their characteristics including structures, chromosomal location, subcellular locations, regulatory elements, and gene networking were not rigorously studied. Our analysis identified 7 TaDCL, 39 TaAGO, and 16 TaRDR genes as RNA interference (RNAi) genes from the wheat genome. Phylogenetic analysis of predicted RNAi proteins with the RNAi proteins of Arabidopsis and rice showed that the predicted proteins of TaDCL, TaAGO, and TaRDR groups are clustered into four, eight, and four subgroups, respectively. Domain, 3D protein structure, motif, and exon-intron structure analyses showed that these proteins conserve identical characteristics within groups and maintain differences between groups. The nonsynonymous/synonymous mutation ratio (Ka/Ks) < 1 suggested that these protein sequences conserve some purifying functions. RNAi genes networking with TFs revealed that ERF, MIKC-MADS, C2H2, BBR-BPC, MYB, and Dof are the key transcriptional regulators of the predicted RNAi-related genes. The cis-regulatory element (CREs) analysis detected some important CREs of RNAi genes that are significantly associated with light, stress, and hormone responses. Expression analysis based on an online database exhibited that almost all of the predicted RNAi genes are expressed in different tissues and organs. A case-control study from the gene expression level showed that some RNAi genes significantly responded to the drought and heat stresses. Overall results would therefore provide an excellent basis for in-depth molecular investigation of these genes and their regulatory elements for wheat crop improvement against different stressors.
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8
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Uslu VV, Dalakouras A, Steffens VA, Krczal G, Wassenegger M. High-pressure sprayed siRNAs influence the efficiency but not the profile of transitive silencing. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2022; 109:1199-1212. [PMID: 34882879 DOI: 10.1111/tpj.15625] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 11/18/2021] [Accepted: 11/26/2021] [Indexed: 06/13/2023]
Abstract
In plants, small interfering RNAs (siRNAs) are a quintessential class of RNA interference (RNAi)-inducing molecules produced by the endonucleolytic cleavage of double-stranded RNAs (dsRNAs). In order to ensure robust RNAi, siRNAs are amplified through a positive feedback mechanism called transitivity. Transitivity relies on RNA-DIRECTED RNA POLYMERASE 6 (RDR6)-mediated dsRNA synthesis using siRNA-targeted RNA. The newly synthesized dsRNA is subsequently cleaved into secondary siRNAs by DICER-LIKE (DCL) endonucleases. Just like primary siRNAs, secondary siRNAs are also loaded into ARGONAUTE proteins (AGOs) to form an RNA-induced silencing complex reinforcing the cleavage of the target RNA. Although the molecular players underlying transitivity are well established, the mode of action of transitivity remains elusive. In this study, we investigated the influence of primary target sites on transgene silencing and transitivity using the green fluorescent protein (GFP)-expressing Nicotiana benthamiana 16C line, high-pressure spraying protocol, and synthetic 22-nucleotide (nt) long siRNAs. We found that the 22-nt siRNA targeting the 3' of the GFP transgene was less efficient in inducing silencing when compared with the siRNAs targeting the 5' and middle region of the GFP. Moreover, sRNA sequencing of locally silenced leaves showed that the amount but not the profile of secondary RNAs is shaped by the occupancy of the primary siRNA triggers on the target RNA. Our findings suggest that RDR6-mediated dsRNA synthesis is not primed by primary siRNAs and that dsRNA synthesis appears to be generally initiated at the 3'-end of the target RNA.
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Affiliation(s)
- Veli Vural Uslu
- AlPlanta-Institute for Plant Research, RLP AgroScience GmbH, Neustadt an der Weinstraße, Germany
| | - Athanasios Dalakouras
- Institute of Industrial and Forage Crops, Hellenic Agricultural Organization ELGO-DEMETER, Larissa, Greece
| | - Victor A Steffens
- AlPlanta-Institute for Plant Research, RLP AgroScience GmbH, Neustadt an der Weinstraße, Germany
| | - Gabi Krczal
- AlPlanta-Institute for Plant Research, RLP AgroScience GmbH, Neustadt an der Weinstraße, Germany
| | - Michael Wassenegger
- AlPlanta-Institute for Plant Research, RLP AgroScience GmbH, Neustadt an der Weinstraße, Germany
- Centre for Organismal Studies Heidelberg, University of Heidelberg, Heidelberg, Germany
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9
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Paudel L, Kerr S, Prentis P, Tanurdžić M, Papanicolaou A, Plett JM, Cazzonelli CI. Horticultural innovation by viral-induced gene regulation of carotenogenesis. HORTICULTURE RESEARCH 2022; 9:uhab008. [PMID: 35043183 PMCID: PMC8769041 DOI: 10.1093/hr/uhab008] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 08/31/2021] [Accepted: 09/24/2021] [Indexed: 06/14/2023]
Abstract
Multipartite viral vectors provide a simple, inexpensive and effective biotechnological tool to transiently manipulate (i.e. reduce or increase) gene expression in planta and characterise the function of genetic traits. The development of virus-induced gene regulation (VIGR) systems usually involve the targeted silencing or overexpression of genes involved in pigment biosynthesis or degradation in plastids, thereby providing rapid visual assessment of success in establishing RNA- or DNA-based VIGR systems in planta. Carotenoids pigments provide plant tissues with an array of yellow, orange, and pinkish-red colours. VIGR-induced transient manipulation of carotenoid-related gene expression has advanced our understanding of carotenoid biosynthesis, regulation, accumulation and degradation, as well as plastid signalling processes. In this review, we describe mechanisms of VIGR, the importance of carotenoids as visual markers of technology development, and knowledge gained through manipulating carotenogenesis in model plants as well as horticultural crops not always amenable to transgenic approaches. We outline how VIGR can be utilised in plants to fast-track the characterisation of gene function(s), accelerate fruit tree breeding programs, edit genomes, and biofortify plant products enriched in carotenoid micronutrients for horticultural innovation.
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Affiliation(s)
- Lucky Paudel
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith NSW 2751, Australia
| | - Stephanie Kerr
- Centre for Agriculture and the Bioeconomy (CAB), Queensland University of Technology, 2 George Street, Brisbane City, QLD 4000, Australia
- School of Biology and Environmental Sciences, Faculty of Science,
Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia
| | - Peter Prentis
- Centre for Agriculture and the Bioeconomy (CAB), Queensland University of Technology, 2 George Street, Brisbane City, QLD 4000, Australia
- School of Biology and Environmental Sciences, Faculty of Science,
Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia
| | - Miloš Tanurdžić
- School of Biological Sciences, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Alexie Papanicolaou
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith NSW 2751, Australia
| | - Jonathan M Plett
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith NSW 2751, Australia
| | - Christopher I Cazzonelli
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith NSW 2751, Australia
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10
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Annacondia ML, Martinez G. Reprogramming of RNA silencing triggered by cucumber mosaic virus infection in Arabidopsis. Genome Biol 2021; 22:340. [PMID: 34911561 PMCID: PMC8672585 DOI: 10.1186/s13059-021-02564-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Accepted: 12/02/2021] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND RNA silencing has an important role mediating sequence-specific virus resistance in plants. The complex interaction of viruses with RNA silencing involves the loading of viral small interfering RNAs (vsiRNAs) into its host ARGONAUTE (AGO) proteins. As a side effect of their antiviral activity, vsiRNAs loading into AGO proteins can also mediate the silencing of endogenous genes. Here, we analyze at the genome-wide level both aspects of the interference of cucumber mosaic virus (CMV) with the RNA silencing machinery of Arabidopsis thaliana. RESULTS We observe CMV-derived vsiRNAs affect the levels of endogenous sRNA classes. Furthermore, we analyze the incorporation of vsiRNAs into AGO proteins with a described antiviral role and the viral suppressor of RNA silencing (VSR) 2b, by combining protein immunoprecipitation with sRNA high-throughput sequencing. Interestingly, vsiRNAs represent a substantial percentage of AGO-loaded sRNAs and displace other endogenous sRNAs. As a countermeasure, the VSR 2b loaded vsiRNAs and mRNA-derived siRNAs, which affect the expression of the genes they derive from. Additionally, we analyze how vsiRNAs incorporate into the endogenous RNA silencing pathways by exploring their target mRNAs using parallel analysis of RNA end (PARE) sequencing, which allow us to identify vsiRNA-targeted genes genome-wide. CONCLUSIONS This work exemplifies the complex relationship of RNA viruses with the endogenous RNA silencing machinery and the multiple aspects of virus resistance and virulence that this interaction induces.
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Affiliation(s)
- Maria Luz Annacondia
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden
| | - German Martinez
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences and Linnean Center for Plant Biology, Uppsala, Sweden.
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11
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Wang Y, Gong Q, Wu Y, Huang F, Ismayil A, Zhang D, Li H, Gu H, Ludman M, Fátyol K, Qi Y, Yoshioka K, Hanley-Bowdoin L, Hong Y, Liu Y. A calmodulin-binding transcription factor links calcium signaling to antiviral RNAi defense in plants. Cell Host Microbe 2021; 29:1393-1406.e7. [PMID: 34352216 DOI: 10.1016/j.chom.2021.07.003] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Revised: 05/20/2021] [Accepted: 07/06/2021] [Indexed: 10/20/2022]
Abstract
RNA interference (RNAi) is an across-kingdom gene regulatory and defense mechanism. However, little is known about how organisms sense initial cues to mobilize RNAi. Here, we show that wounding to Nicotiana benthamiana cells during virus intrusion activates RNAi-related gene expression through calcium signaling. A rapid wound-induced elevation in calcium fluxes triggers calmodulin-dependent activation of calmodulin-binding transcription activator-3 (CAMTA3), which activates RNA-dependent RNA polymerase-6 and Bifunctional nuclease-2 (BN2) transcription. BN2 stabilizes mRNAs encoding key components of RNAi machinery, notably AGONAUTE1/2 and DICER-LIKE1, by degrading their cognate microRNAs. Consequently, multiple RNAi genes are primed for combating virus invasion. Calmodulin-, CAMTA3-, or BN2-knockdown/knockout plants show increased susceptibility to geminivirus, cucumovirus, and potyvirus. Notably, Geminivirus V2 protein can disrupt the calmodulin-CAMTA3 interaction to counteract RNAi defense. These findings link Ca2+ signaling to RNAi and reveal versatility of host antiviral defense and viral counter-defense.
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Affiliation(s)
- Yunjing Wang
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Qian Gong
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Yuyao Wu
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Fan Huang
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Asigul Ismayil
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Danfeng Zhang
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Huangai Li
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Hanqing Gu
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Márta Ludman
- Institute of Genetics and Biotechnology, Hungarian University of Agriculture and Life Sciences, Szent-Györgyi Albert u. 4, Gödöllő 2100, Hungary
| | - Károly Fátyol
- Institute of Genetics and Biotechnology, Hungarian University of Agriculture and Life Sciences, Szent-Györgyi Albert u. 4, Gödöllő 2100, Hungary
| | - Yijun Qi
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China
| | - Keiko Yoshioka
- Department of Cell and Systems Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada
| | - Linda Hanley-Bowdoin
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh NC 27695, USA
| | - Yiguo Hong
- Research Centre for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 311121, China; School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK; School of Science and the Environment, University of Worcester, Worcester WR2 6AJ, UK
| | - Yule Liu
- MOE Key Laboratory of Bioinformatics and Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Center for Life Sciences, Beijing 100084, China.
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12
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Viroids as a Tool to Study RNA-Directed DNA Methylation in Plants. Cells 2021; 10:cells10051187. [PMID: 34067940 PMCID: PMC8152041 DOI: 10.3390/cells10051187] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Revised: 05/10/2021] [Accepted: 05/10/2021] [Indexed: 12/11/2022] Open
Abstract
Viroids are plant pathogenic, circular, non-coding, single-stranded RNAs (ssRNAs). Members of the Pospiviroidae family replicate in the nucleus of plant cells through double-stranded RNA (dsRNA) intermediates, thus triggering the host’s RNA interference (RNAi) machinery. In plants, the two RNAi pillars are Post-Transcriptional Gene Silencing (PTGS) and RNA-directed DNA Methylation (RdDM), and the latter has the potential to trigger Transcriptional Gene Silencing (TGS). Over the last three decades, the employment of viroid-based systems has immensely contributed to our understanding of both of these RNAi facets. In this review, we highlight the role of Pospiviroidae in the discovery of RdDM, expound the gradual elucidation through the years of the diverse array of RdDM’s mechanistic details and propose a revised RdDM model based on the cumulative amount of evidence from viroid and non-viroid systems.
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13
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Sanan-Mishra N, Abdul Kader Jailani A, Mandal B, Mukherjee SK. Secondary siRNAs in Plants: Biosynthesis, Various Functions, and Applications in Virology. FRONTIERS IN PLANT SCIENCE 2021; 12:610283. [PMID: 33737942 PMCID: PMC7960677 DOI: 10.3389/fpls.2021.610283] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 01/18/2021] [Indexed: 05/13/2023]
Abstract
The major components of RNA silencing include both transitive and systemic small RNAs, which are technically called secondary sRNAs. Double-stranded RNAs trigger systemic silencing pathways to negatively regulate gene expression. The secondary siRNAs generated as a result of transitive silencing also play a substantial role in gene silencing especially in antiviral defense. In this review, we first describe the discovery and pathways of transitivity with emphasis on RNA-dependent RNA polymerases followed by description on the short range and systemic spread of silencing. We also provide an in-depth view on the various size classes of secondary siRNAs and their different roles in RNA silencing including their categorization based on their biogenesis. The other regulatory roles of secondary siRNAs in transgene silencing, virus-induced gene silencing, transitivity, and trans-species transfer have also been detailed. The possible implications and applications of systemic silencing and the different gene silencing tools developed are also described. The details on mobility and roles of secondary siRNAs derived from viral genome in plant defense against the respective viruses are presented. This entails the description of other compatible plant-virus interactions and the corresponding small RNAs that determine recovery from disease symptoms, exclusion of viruses from shoot meristems, and natural resistance. The last section presents an overview on the usefulness of RNA silencing for management of viral infections in crop plants.
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Affiliation(s)
- Neeti Sanan-Mishra
- Plant RNAi Biology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
| | - A. Abdul Kader Jailani
- Plant RNAi Biology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
- Advanced Center for Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi, India
| | - Bikash Mandal
- Advanced Center for Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi, India
| | - Sunil K. Mukherjee
- Advanced Center for Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi, India
- *Correspondence: Sunil K. Mukherjee,
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14
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Naoi T, Kitabayashi S, Kasai A, Sugawara K, Adkar-Purushothama CR, Senda M, Hataya T, Sano T. Suppression of RNA-dependent RNA polymerase 6 in tomatoes allows potato spindle tuber viroid to invade basal part but not apical part including pluripotent stem cells of shoot apical meristem. PLoS One 2020; 15:e0236481. [PMID: 32716919 PMCID: PMC7384629 DOI: 10.1371/journal.pone.0236481] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 07/06/2020] [Indexed: 01/29/2023] Open
Abstract
RNA-dependent RNA polymerase 6 (RDR6) is one of the key factors in plant defense responses and suppresses virus or viroid invasion into shoot apical meristem (SAM) in Nicotiana benthamiana. To evaluate the role of Solanum lycopersicum (Sl) RDR6 upon viroid infection, SlRDR6-suppressed (SlRDR6i) ‘Moneymaker’ tomatoes were generated by RNA interference and inoculated with intermediate or lethal strain of potato spindle tuber viroid (PSTVd). Suppression of SlRDR6 did not change disease symptoms of both PSTVd strains in ‘Moneymaker’ tomatoes. Analysis of PSTVd distribution in shoot apices by in situ hybridization revealed that both PSTVd strains similarly invade the basal part but not apical part including pluripotent stem cells of SAM in SlRDR6i plants at a low rate unlike a previous report in N. benthamiana. In addition, unexpectedly, amount of PSTVd accumulation was apparently lower in SlRDR6i plants than in control tomatoes transformed with empty cassette in early infection especially in the lethal strain. Meanwhile, SlRDR6 suppression did not affect the seed transmission rates of PSTVd. These results indicate that RDR6 generally suppresses PSTVd invasion into SAM in plants, while suppression of RDR6 does not necessarily elevate amount of PSTVd accumulation. Additionally, our results suggest that host factors such as RDR1 other than RDR6 may also be involved in the protection of SAM including pluripotent stem cells from PSTVd invasion and effective RNA silencing causing the decrease of PSTVd accumulation during early infection in tomato plants.
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Affiliation(s)
- Takashi Naoi
- Graduate School of Agriculture, Hokkaido University, Sapporo, Japan
| | - Syoya Kitabayashi
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
| | - Atsushi Kasai
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
| | - Kohei Sugawara
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
| | - Charith Raj Adkar-Purushothama
- Département de Biochimie, Faculté de Médecine des Sciences de la Santé, Pavillon de Recherche Appliquée au Cancer, Université de Sherbrooke, Sherbrooke, Québec, Canada
| | - Mineo Senda
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
| | - Tatsuji Hataya
- Graduate School of Agriculture, Hokkaido University, Sapporo, Japan
- Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan
- * E-mail: (TH); (TS)
| | - Teruo Sano
- Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan
- * E-mail: (TH); (TS)
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15
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Abstract
Virus-induced gene silencing (VIGS) is a powerful tool for rapidly knocking down the expression of plant genes to elucidate functional genomics. We have established a VIGS vector for monocot plants derived from Foxtail mosaic virus (FoMV), a positive-sense single-stranded RNA virus. For silencing a targeted gene, plant gene fragment was inserted into the vector between open reading frame 4 (ORF4) and ORF5 under the control of a duplicated coat protein promoter. Plants of different monocot species were infected by mechanical inoculation with sap from FoMV derivative-infected Chenopodium quinoa leaves. Gene silencing was typically observed within 2-3 weeks after inoculation. In this chapter, we describe the detailed protocol for silencing a target gene in various Poaceae plants by using FoMV-based vectors.
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16
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Fátyol K, Fekete KA, Ludman M. Double-Stranded-RNA-Binding Protein 2 Participates in Antiviral Defense. J Virol 2020; 94:e00017-20. [PMID: 32213615 PMCID: PMC7269452 DOI: 10.1128/jvi.00017-20] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2020] [Accepted: 03/17/2020] [Indexed: 01/01/2023] Open
Abstract
Double-stranded RNA (dsRNA) is a common pattern formed during the replication of both RNA and DNA viruses. Perception of virus-derived dsRNAs by specialized receptor molecules leads to the activation of various antiviral measures. In plants, these defensive processes include the adaptive RNA interference (RNAi) pathway and innate pattern-triggered immune (PTI) responses. While details of the former process have been well established in recent years, the latter are still only partially understood at the molecular level. Nonetheless, emerging data suggest extensive cross talk between the different antiviral mechanisms. Here, we demonstrate that dsRNA-binding protein 2 (DRB2) of Nicotiana benthamiana plays a direct role in potato virus X (PVX)-elicited systemic necrosis. These results establish that DRB2, a known component of RNAi, is also involved in a virus-induced PTI response. In addition, our findings suggest that RNA-dependent polymerase 6 (RDR6)-dependent dsRNAs play an important role in the triggering of PVX-induced systemic necrosis. Based on our data, a model is formulated whereby competition between different DRB proteins for virus-derived dsRNAs helps establish the dominant antiviral pathways that are activated in response to virus infection.IMPORTANCE Plants employ multiple defense mechanisms to restrict viral infections, among which RNA interference is the best understood. The activation of innate immunity often leads to both local and systemic necrotic responses, which confine the virus to the infected cells and can also provide resistance to distal, noninfected parts of the organism. Systemic necrosis, which is regarded as a special form of the local hypersensitive response, results in necrosis of the apical stem region, usually causing the death of the plant. Here, we provide evidence that the dsRNA-binding protein 2 of Nicotiana benthamiana plays an important role in virus-induced systemic necrosis. Our findings are not only compatible with the recent hypothesis that DRB proteins act as viral invasion sensors but also extends it by proposing that DRBs play a critical role in establishing the dominant antiviral measures that are triggered during virus infection.
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Affiliation(s)
- Károly Fátyol
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation, Gödöllő, Hungary
| | - Katalin Anna Fekete
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation, Gödöllő, Hungary
| | - Márta Ludman
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation, Gödöllő, Hungary
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17
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Ludman M, Fátyol K. The virological model plant, Nicotiana benthamiana expresses a single functional RDR6 homeolog. Virology 2019; 537:143-148. [PMID: 31493652 DOI: 10.1016/j.virol.2019.08.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 08/15/2019] [Accepted: 08/18/2019] [Indexed: 01/31/2023]
Abstract
The RNA dependent RNA polymerase, RDR6 is involved in a variety of processes including the biogenesis of endogenous regulatory small RNAs, maintaining post-transcriptional gene silencing of transgenes and establishing efficient antiviral RNA silencing. In the virological model plant, Nicotiana benthamiana, functional studies of RDR6 has so far only been depended on RNAi based methodologies. These techniques however have inherent limitations, especially in the context of antiviral RNA silencing. To overcome this issue, we created rdr6 mutant N. benthamiana by the CRISPR/Cas9 genome editing system. Using the mutant, most of the proposed functions of RDR6 was confirmed. Additionally, the rdr6 N. benthamiana plant recapitulated closely the phenotype of the equivalent Arabidopsis mutant. In summary, the rdr6 N. benthamiana described here may be employed as a model system not only for the better understanding of the role of RDR6 in pathogen elicited immune responses but in various developmental processes as well.
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Affiliation(s)
- Márta Ludman
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, Szent-Györgyi Albert u. 4, Gödöllő, 2100, Hungary
| | - Károly Fátyol
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, Szent-Györgyi Albert u. 4, Gödöllő, 2100, Hungary.
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18
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Wang Y, Qiao R, Wei C, Li Y. Rice Dwarf Virus Small RNA Profiles in Rice and Leafhopper Reveal Distinct Patterns in Cross-Kingdom Hosts. Viruses 2019; 11:v11090847. [PMID: 31547224 PMCID: PMC6784124 DOI: 10.3390/v11090847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 09/03/2019] [Accepted: 09/07/2019] [Indexed: 11/16/2022] Open
Abstract
RNA silencing has evolved as a widespread antiviral strategy in many eukaryotic organisms. Antiviral RNA silencing is mediated by virus-derived small RNAs (vsiRNAs), created by the cleavage of double-stranded viral RNA substrates by Dicer (Dcr) in animals or Dicer-like (DCL) proteins in plants. However, little is known about how the RNA silencing mechanisms of different hosts respond to the same virus infection. We performed high-throughput small RNA sequencing in Nephotettix cincticeps and Oryza sativa infected with Rice dwarf phytoreovirus and analyzed the distinct accumulation of vsiRNAs in these two hosts. The results suggested a potential branch in the evolution of antiviral RNA silencing of insect and plant hosts. The rice vsiRNAs were predominantly 21 and 22 nucleotides (nt) long, suggesting that OsDCL4 and OsDCL2 are involved in their production, whereas 21-nt vsiRNAs dominated in leafhopper, suggesting the involvement of a Dcr-2 homolog. Furthermore, we identified ~50-fold more vsiRNAs in rice than in leafhoppers, which might be partially attributable to the activity of RNA-dependent RNA polymerase 6 (RDR6) in rice and the lack of RDR genes in leafhoppers. Our data established a basis for further comparative studies on the evolution of RNA silencing-based interactions between a virus and its hosts, across kingdoms.
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Affiliation(s)
- Yu Wang
- State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China
| | - Rui Qiao
- State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China
| | - Chunhong Wei
- State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China
| | - Yi Li
- State Key Laboratory of Protein and Plant Gene Research, College of Life Sciences, Peking University, Beijing 100871, China.
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19
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Matsuo K, Atsumi G. CRISPR/Cas9-mediated knockout of the RDR6 gene in Nicotiana benthamiana for efficient transient expression of recombinant proteins. PLANTA 2019; 250:463-473. [PMID: 31065786 DOI: 10.1007/s00425-019-03180-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Accepted: 04/30/2019] [Indexed: 05/27/2023]
Abstract
MAIN CONCLUSION RDR6 gene knockout Nicotiana benthamiana plant was successfully produced using CRISPR/Cas9 technology. The production of recombinant proteins in plants has many advantages, such as safety and reduced costs. However, there are several problems with this technology, especially low levels of protein production. The dysfunction of the RNA silencing mechanism in plant cells would be effective to improve recombinant protein production because the RNA silencing mechanism efficiently degrades transgene-derived mRNAs. Therefore, to overcome this problem, clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology was used to develop RNA silencing-related gene knockout transgenic Nicotiana benthamiana. We successfully produced RNA-dependent RNA polymerase 6 (RDR6), one of the most important components of the RNA silencing mechanism-knockout N. benthamiana (ΔRDR6 plants). The ΔRDR6 plants had abnormal flowers and were sterile, as with the Arabidopsis RDR6 mutants. However, a transient gene expression assay showed that the ΔRDR6 plants accumulated larger amounts of green fluorescent protein (GFP) and GFP mRNA than the wild-type (WT) plants. Small RNA sequencing analysis revealed that levels of small interfering RNA against the GFP gene were greatly reduced in the ΔRDR6 plants, as compared to that of the WT plants. These findings demonstrate that the ΔRDR6 plants can express larger amounts of recombinant proteins than WT plants and, therefore, would be useful for recombinant protein production and understanding the contributions of RDR6 to genetic and physiological events in plants.
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Affiliation(s)
- Kouki Matsuo
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, 062-8517, Japan.
| | - Go Atsumi
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, 062-8517, Japan
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20
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Genome-Wide Analysis of DCL, AGO, and RDR Gene Families in Pepper (Capsicum Annuum L.). Int J Mol Sci 2018; 19:ijms19041038. [PMID: 29601523 PMCID: PMC5979589 DOI: 10.3390/ijms19041038] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2018] [Revised: 03/26/2018] [Accepted: 03/27/2018] [Indexed: 12/18/2022] Open
Abstract
RNA silencing is an evolutionarily conserved mechanism that regulates variety of cellular processes in plants. Argonaute protein (AGO), Dicer-like protein (DCL) and RNA-dependent RNA polymerase (RDR) are critical components of RNA silencing. These efficient and indispensable components of the RNAi pathway have not been identified and characterized in pepper. In this study, we identified 12 CaAGO, 4 CaDCL and 6 CaRDR genes in pepper and compared them with those of Arabidopsis, tobacco, potato and tomato. Detailed phylogenetic analyses revealed that each CaAGO, CaDCL and CaRDR protein family were classified into four clades. The tissue specific expression and respond to abiotic or biotic stress were studied. The real-time quantitative polymerase chain reaction (PCR) results demonstrated that CaAGO2, CaAGO10b, CaDCL2 and CaDCL4 were upregulated with cucumber mosaic virus (CMV), potato virus Y (PVY) and tobacco mosaic virus (TMV) infections, whereas they showed difference expression patterns in response to abiotic stress. In addition, we found that many of the candidate genes were induced by phytohormones and H2O2 treatment. Our results provide useful information for further elucidation of gene silencing pathways and RNAi-mediated host immunity in pepper.
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21
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Malpica-López N, Rajeswaran R, Beknazariants D, Seguin J, Golyaev V, Farinelli L, Pooggin MM. Revisiting the Roles of Tobamovirus Replicase Complex Proteins in Viral Replication and Silencing Suppression. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2018; 31:125-144. [PMID: 29140168 DOI: 10.1094/mpmi-07-17-0164-r] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Tobamoviral replicase possesses an RNA-dependent RNA polymerase (RDR) domain and is translated from genomic (g)RNA via a stop codon readthrough mechanism at a one-to-ten ratio relative to a shorter protein lacking the RDR domain. The two proteins share methyltransferase and helicase domains and form a heterodimer implicated in gRNA replication. The shorter protein is also implicated in suppressing RNA silencing-based antiviral defenses. Using a stop codon mutant of Oilseed rape mosaic tobamovirus (ORMV), we demonstrate that the readthrough replicase (p182) is sufficient for gRNA replication and for subgenomic RNA transcription during systemic infection in Nicotiana benthamiana and Arabidopsis thaliana. However, the mutant virus displays milder symptoms and does not interfere with HEN1-mediated methylation of viral short interfering (si)RNAs or plant small (s)RNAs. The mutant virus tends to revert the stop codon, thereby restoring expression of the shorter protein (p125), even in the absence of plant Dicer-like activities that generate viral siRNAs. Plant RDR activities that generate endogenous siRNA precursors do not prevent replication or movement of the mutant virus, and double-stranded precursors of viral siRNAs representing the entire virus genome are likely synthesized by p182. Transgenic expression of p125 partially recapitulates the ORMV disease symptoms associated with overaccumulation of plant sRNAs. Taken together, the readthrough replicase p182 is sufficient for viral replication and transcription but not for silencing suppression. By contrast, the shorter p125 protein suppresses silencing, provokes severe disease symptoms, causes overaccumulation of unmethylated viral and plant sRNAs but it is not an essential component of the viral replicase complex.
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Affiliation(s)
| | | | - Daria Beknazariants
- 1 University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | - Jonathan Seguin
- 1 University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | - Victor Golyaev
- 1 University of Basel, Department of Environmental Sciences, Basel, Switzerland
| | | | - Mikhail M Pooggin
- 1 University of Basel, Department of Environmental Sciences, Basel, Switzerland
- 3 INRA, UMR BGPI, Montpellier, France
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22
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Chang F, Gu Z, Zhu P, Lu R, Du Z, Liao Q. Reduction of RNA-dependent RNA polymerase 6 in Nicotiana benthamiana enhances gene silencing induced by Foxtail mosaic virus. Acta Biochim Biophys Sin (Shanghai) 2017; 49:652-654. [PMID: 28541405 DOI: 10.1093/abbs/gmx050] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Indexed: 11/14/2022] Open
Affiliation(s)
| | | | - Pin Zhu
- College of Life Sciences, Zhejiang SCI-Tech University, Hangzhou 310018, China
| | - Ran Lu
- College of Life Sciences, Zhejiang SCI-Tech University, Hangzhou 310018, China
| | - Zhiyou Du
- College of Life Sciences, Zhejiang SCI-Tech University, Hangzhou 310018, China
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23
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Abstract
Biological processes such as defense mechanisms and microbial offense strategies are regulated through RNA induced interference in eukaryotes. Genetic mutations are modulated through biogenesis of small RNAs which directly impacts upon host development. Plant defense mechanisms are regulated and supported by a diversified group of small RNAs which are involved in streamlining several RNA interference pathways leading toward the initiation of pathogen gene silencing mechanisms. In the similar context, pathogens also utilize the support of small RNAs to launch their offensive attacks. Also there are strong evidences about the active involvement of these RNAs in symbiotic associations. Interestingly, small RNAs are not limited to the individuals in whom they are produced; they also show cross kingdom influences through variable interactions with other species thus leading toward the inter-organismic gene silencing. The phenomenon is understandable in the microbes which utilize these mechanisms to overcome host defense line. Understanding the mechanism of triggering host defense strategies can be a valuable step toward the generation of disease resistant host plants. We think that the cross kingdom trafficking of small RNA is an interesting insight that is needed to be explored for its vitality.
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Affiliation(s)
- Waqar Islam
- a College of Plant Protection , Fujian Agriculture and Forestry University , Fuzhou , Fujian , China
| | - Saif Ul Islam
- a College of Plant Protection , Fujian Agriculture and Forestry University , Fuzhou , Fujian , China
| | - Muhammad Qasim
- a College of Plant Protection , Fujian Agriculture and Forestry University , Fuzhou , Fujian , China
| | - Liande Wang
- a College of Plant Protection , Fujian Agriculture and Forestry University , Fuzhou , Fujian , China
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24
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Ludman M, Burgyán J, Fátyol K. Crispr/Cas9 Mediated Inactivation of Argonaute 2 Reveals its Differential Involvement in Antiviral Responses. Sci Rep 2017; 7:1010. [PMID: 28432338 PMCID: PMC5430636 DOI: 10.1038/s41598-017-01050-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Accepted: 03/17/2017] [Indexed: 12/21/2022] Open
Abstract
RNA silencing constitutes an important antiviral mechanism in plants. Small RNA guided Argonaute proteins fulfill essential role in this process by acting as executors of viral restriction. Plants encode multiple Argonaute proteins of which several exhibit antiviral activities. A recent addition to this group is AGO2. Its involvement in antiviral responses is established predominantly by studies employing mutants of Arabidopsis thaliana. In the virological model plant, Nicotiana benthamiana, the contribution of AGO2 to antiviral immunity is much less certain due to the lack of appropriate genetic mutants. Previous studies employed various RNAi based tools to down-regulate AGO2 expression. However, these techniques have several disadvantages, especially in the context of antiviral RNA silencing. Here, we have utilized the CRISPR/Cas9 technology to inactivate the AGO2 gene of N. benthamiana. The ago2 plants exhibit differential sensitivities towards various viruses. AGO2 is a critical component of the plants' immune responses against PVX, TuMV and TCV. In contrast, AGO2 deficiency does not significantly influence the progression of tombusvirus and CMV infections. In summary, our work provides unequivocal proof for the virus-specific antiviral role of AGO2 in a plant species other than A. thaliana for the first time.
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Affiliation(s)
- Márta Ludman
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, Szent-Györgyi Albert u. 4, Gödöllő, 2100, Hungary
| | - József Burgyán
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, Szent-Györgyi Albert u. 4, Gödöllő, 2100, Hungary.
| | - Károly Fátyol
- Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, Szent-Györgyi Albert u. 4, Gödöllő, 2100, Hungary.
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25
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Cheng X, Wang A. The Potyvirus Silencing Suppressor Protein VPg Mediates Degradation of SGS3 via Ubiquitination and Autophagy Pathways. J Virol 2017; 91:e01478-16. [PMID: 27795417 PMCID: PMC5165207 DOI: 10.1128/jvi.01478-16] [Citation(s) in RCA: 116] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 10/17/2016] [Indexed: 12/31/2022] Open
Abstract
RNA silencing is an innate antiviral immunity response of plants and animals. To counteract this host immune response, viruses have evolved an effective strategy to protect themselves by the expression of viral suppressors of RNA silencing (VSRs). Most potyviruses encode two VSRs, helper component-proteinase (HC-Pro) and viral genome-linked protein (VPg). The molecular biology of the former has been well characterized, whereas how VPg exerts its function in the suppression of RNA silencing is yet to be understood. In this study, we show that infection by Turnip mosaic virus (TuMV) causes reduced levels of suppressor of gene silencing 3 (SGS3), a key component of the RNA silencing pathway that functions in double-stranded RNA synthesis for virus-derived small interfering RNA (vsiRNA) production. We also demonstrate that among 11 TuMV-encoded viral proteins, VPg is the only one that interacts with SGS3. We furthermore present evidence that the expression of VPg alone, independent of viral infection, is sufficient to induce the degradation of SGS3 and its intimate partner RNA-dependent RNA polymerase 6 (RDR6). Moreover, we discover that the VPg-mediated degradation of SGS3 occurs via both the 20S ubiquitin-proteasome and autophagy pathways. Taken together, our data suggest a role for VPg-mediated degradation of SGS3 in suppression of silencing by VPg. IMPORTANCE Potyviruses represent the largest group of known plant viruses and cause significant losses of many agriculturally important crops in the world. In order to establish infection, potyviruses must overcome the host antiviral silencing response. A viral protein called VPg has been shown to play a role in this process, but how it works is unclear. In this paper, we found that the VPg protein of Turnip mosaic virus (TuMV), which is a potyvirus, interacts with a host protein named SGS3, a key protein in the RNA silencing pathway. Moreover, this interaction leads to the degradation of SGS3 and its interacting and functional partner RDR6, which is another essential component of the RNA silencing pathway. We also identified the cellular pathways that are recruited for the VPg-mediated degradation of SGS3. Therefore, this work reveals a possible mechanism by which VPg sabotages host antiviral RNA silencing to promote virus infection.
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Affiliation(s)
- Xiaofei Cheng
- London Research and Development Centre, Agriculture and Agri-Food Canada, London, Ontario, Canada
| | - Aiming Wang
- London Research and Development Centre, Agriculture and Agri-Food Canada, London, Ontario, Canada
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Fang YY, Zhao JH, Liu SW, Wang S, Duan CG, Guo HS. CMV2b-AGO Interaction Is Required for the Suppression of RDR-Dependent Antiviral Silencing in Arabidopsis. Front Microbiol 2016; 7:1329. [PMID: 27605926 PMCID: PMC4995204 DOI: 10.3389/fmicb.2016.01329] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 08/11/2016] [Indexed: 12/02/2022] Open
Abstract
Using a transient plant system, it was previously found that the suppression of Cucumber mosaic virus (CMV) 2b protein relies on its double-strand (ds) RNA binding capacity, but it is independent of its interaction with ARGONAUTE (AGO) proteins. Thus, the biological meaning of the 2b-AGO interaction in the context of virus infection remains elusive. In this study, we created infectious clones of CMV mutants that expressed the 2b functional domains of dsRNA or AGO binding and tested the effect of these CMV mutants on viral pathogenicity. We found that the mutant CMV2b(1–76) expressing the 2b dsRNA-binding domain exhibited the same virulence as wild-type CMV in infection with either wild-type Arabidopsis or rdr1/6 plants with RDR1- and RDR6-deficient mutations. However, remarkably reduced viral RNA levels and increased virus (v)siRNAs were detected in CMV2b(1–76)-infected Arabidopsis in comparison to CMV infection, which demonstrated that the 2b(1–76) deleted AGO-binding domain failed to suppress the RDR1/RDR6-dependent degradation of viral RNAs. The mutant CMV2b(8–111) expressing mutant 2b, in which the N-terminal 7 amino acid (aa) was deleted, exhibited slightly reduced virulence, but not viral RNA levels, in both wild-type and rdr1/6 plants, which indicated that 2b retained the AGO-binding activity acquired the counter-RDRs degradation of viral RNAs. The deletion of the N-terminal 7 aa of 2b affected virulence due to the reduced affinity for long dsRNA. The mutant CMV2b(18–111) expressing mutant 2b lacked the N-terminal 17 aa but retained its AGO-binding activity greatly reduced virulence and viral RNA level. Together with the instability of both 2b(18–111)-EGFP and RFP-AGO4 proteins when co-expressed in Nicotiana benthamiana leaves, our data demonstrates that the effect of 2b-AGO interaction on counter-RDRs antiviral defense required the presence of 2b dsRNA-binding activity. Taken together, our findings demonstrate that the dsRNA-binding activity of the 2b was essential for virulence, whereas the 2b-AGO interaction was necessary for interference with RDR1/6-dependent antiviral silencing in Arabidopsis.
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Affiliation(s)
- Yuan-Yuan Fang
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences Beijing, China
| | - Jian-Hua Zhao
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences Beijing, China
| | - Shang-Wu Liu
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of SciencesBeijing, China; Virus-free Seedling Research Institute, Heilongjiang Academy of Agricultural SciencesHarbin, China
| | - Sheng Wang
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences Beijing, China
| | - Cheng-Guo Duan
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences Beijing, China
| | - Hui-Shan Guo
- State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of SciencesBeijing, China; College of Life Sciences, University of Chinese Academy of SciencesBeijing, China
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Mann KS, Johnson KN, Carroll BJ, Dietzgen RG. Cytorhabdovirus P protein suppresses RISC-mediated cleavage and RNA silencing amplification in planta. Virology 2016; 490:27-40. [PMID: 26808923 DOI: 10.1016/j.virol.2016.01.003] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Revised: 01/05/2016] [Accepted: 01/09/2016] [Indexed: 11/16/2022]
Abstract
Plant viruses have evolved to undermine the RNA silencing pathway by expressing suppressor protein(s) that interfere with one or more key components of this antiviral defense. Here we show that the recently identified RNA silencing suppressor (RSS) of lettuce necrotic yellows virus (LNYV), phosphoprotein P, binds to RNA silencing machinery proteins AGO1, AGO2, AGO4, RDR6 and SGS3 in protein-protein interaction assays when transiently expressed. In planta, we demonstrate that LNYV P inhibits miRNA-guided AGO1 cleavage and translational repression, and RDR6/SGS3-dependent amplification of silencing. Analysis of LNYV P deletion mutants identified a C-terminal protein domain essential for both local RNA silencing suppression and interaction with AGO1, AGO2, AGO4, RDR6 and SGS3. In contrast to other viral RSS known to disrupt AGO activity, LNYV P sequence does not contain any recognizable GW/WG or F-box motifs. This suggests that LNYV P may represent a new class of AGO binding proteins.
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Affiliation(s)
- Krin S Mann
- Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Karyn N Johnson
- School of Biological Sciences, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Bernard J Carroll
- School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia
| | - Ralf G Dietzgen
- Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072, Australia; School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia.
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28
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Dong K, Wang Y, Zhang Z, Chai LX, Tong X, Xu J, Li D, Wang XB. Two amino acids near the N-terminus of Cucumber mosaic virus 2b play critical roles in the suppression of RNA silencing and viral infectivity. MOLECULAR PLANT PATHOLOGY 2016; 17:173-83. [PMID: 25893424 PMCID: PMC6638393 DOI: 10.1111/mpp.12270] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Cucumber mosaic virus (CMV) 2b suppresses RNA silencing primarily through the binding of double-stranded RNA (dsRNA) of varying sizes. However, the biologically active form of 2b remains elusive. Here, we demonstrate that the single and double alanine substitution mutants in the N-terminal 15th leucine and 18th methionine of CMV 2b exhibit drastically attenuated virulence in wild-type plants, but are efficiently rescued in mutant plants defective in RNA-dependent RNA polymerase 6 (RDR6) and Dicer-like 4 (DCL4). Moreover, the transgenic plants of 2b, but not 2blm (L15A/M18A), rescue the high infectivity of CMV-Δ2b through the suppression of antiviral silencing. L15A, M18A or both weaken 2b suppressor activity on local and systemic transgene silencing. In contrast with the high affinity of 2b to short and long dsRNAs, 2blm is significantly compromised in 21-bp duplex small interfering RNA (siRNA) binding ability, but maintains a strong affinity for long dsRNAs. In cross-linking assays, 2b can form dimers, tetramers and oligomers after treatment with glutaraldehyde, whereas 2blm only forms dimers, rather than tetramers and oligomers, in vitro. Together, these findings suggest that L15 and M18 of CMV 2b are required for high affinity to ds-siRNAs and oligomerization activity, which are essential for the suppression activity of 2b on antiviral silencing.
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Affiliation(s)
- Kai Dong
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Ying Wang
- Department of Plant Pathology, China Agricultural University, Beijing, 100193, China
| | - Zhen Zhang
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Long-Xiang Chai
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Xin Tong
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Jin Xu
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Dawei Li
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
| | - Xian-Bing Wang
- State Key Laboratory of Agro-Biotechnology and Ministry of Agriculture Key Laboratory of Soil Microbiology, College of Biological Sciences, China Agricultural University, Beijing, 100193, China
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29
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Ma L, Huang X, Yu R, Jing XL, Xu J, Wu CA, Zhu CX, Liu HM. Elevated Ambient Temperature Differentially Affects Virus Resistance in Two Tobacco Species. PHYTOPATHOLOGY 2016; 106:94-100. [PMID: 26474332 DOI: 10.1094/phyto-11-14-0300-r] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Antiviral defense of plants is usually enhanced by an elevated temperature under natural conditions. In order to better understand this phenomenon, we carried out temperature shift experiments with Nicotiana glutinosa plants that were infected with Potato virus X (PVX) or the necrotic strain of Potato virus Y (PVY(N)). The virus titer of the plants was found to be much lower when they were maintained at 30°C compared with 22°C, particularly in the upper leaves. PVX resistance at 30°C persisted for a short period even when temperature was shifted back to 22°C. In contrast, N. benthamiana lost the virus resistance immediately after the temperature dropped to 22°C. Expression analysis of two RNA-dependent RNA polymerases in N. glutinosa (NgRDR) showed that a 12-day treatment at 30°C increased the expression of NgRDR1, while NgRDR6 was not affected. In addition, the NgRDR6 mRNA level correlated with the PVX titer but was unaffected by PVY(N) infection. These observations indicate that PVX and PVY(N), although they are both RNA viruses, might trigger different defense responses at elevated temperatures. Our study provides valuable data for a better understanding of the temperature-regulated host virus interaction.
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Affiliation(s)
- L Ma
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - X Huang
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - R Yu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - X L Jing
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - J Xu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - C A Wu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - C X Zhu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
| | - H M Liu
- State Key Laboratory of Crop Biology, College of Life Sciences, Shandong Agricultural University, Tai'an, Shandong, China
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Mungbean yellow mosaic Indian virus encoded AC2 protein suppresses RNA silencing by inhibiting Arabidopsis RDR6 and AGO1 activities. Virology 2015; 486:158-72. [PMID: 26433748 DOI: 10.1016/j.virol.2015.08.015] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 02/14/2015] [Accepted: 08/15/2015] [Indexed: 12/25/2022]
Abstract
RNA silencing refers to a conserved RNA-directed gene regulatory mechanism in a wide range of eukaryotes. It plays an important role in many processes including growth, development, genome stability, and antiviral defense in the plants. Geminivirus encoded AC2 is identified as an RNA silencing suppressor protein, however, the mechanism of action has not been characterized. In this paper, we elucidate another mechanism of AC2-mediated suppression activity of Mungbean Yellow Mosaic India Virus (MYMIV). The AC2 protein, unlike many other suppressors, does not bind to siRNA or dsRNA species and its suppression activity is mediated through interaction with key components of the RNA silencing pathway, viz., RDR6 and AGO1. AC2 interaction inhibits the RDR6 activity, an essential component of siRNA and tasi-RNA biogenesis and AGO1, the major slicing factor of RISC. Thus the study identifies dual sites of MYMIV-AC2 interference and probably accounts for its strong RNA silencing suppression activity.
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31
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Patil BL, Fauquet CM. Studies on differential behavior of cassava mosaic geminivirus DNA components, symptom recovery patterns, and their siRNA profiles. Virus Genes 2015; 50:474-86. [PMID: 25724177 DOI: 10.1007/s11262-015-1184-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Accepted: 02/18/2015] [Indexed: 11/28/2022]
Abstract
Cassava mosaic disease caused by cassava mosaic geminiviruses (CMGs) with bipartite genome organization is a major constraint for production of cassava in the African continent and the Indian sub-continent. Currently, there are eleven recognized species of CMGs, and several diverse isolates represent them, with vast amount of sequence variability, reflecting into diversity of symptom severity/phenotypes. Here, we make a systematic effort to study the infection dynamics of several species of CMGs and their isolates. Further, we try to identify the genomic component of CMGs contributing to the manifestation of diverse patterns of symptoms and the molecular basis for the differential behavior of CMGs. The pseudo-recombination studies carried out by swapping of DNA-A and DNA-B components of the CMGs revealed that the DNA-B component significantly contributes to the symptom severity. Past studies had shown that the DNA-A component of Sri Lankan cassava mosaic virus shows monopartite feature. Thus, the ability of DNA-A component alone, to replicate and move systemically in the host plant with inherent monopartite features was investigated for all the CMGs. Geminiviruses are known to trigger gene silencing and are also its target, resulting in recovery of the host plant from viral infection. In the collection of several different CMG species and isolates we had, there was a vast variability in their recovery and non-recovery phenotypes. To understand the molecular basis of this, the origin and distribution of virus-derived small interfering RNAs were mapped across their genome and across the CMG-infected symptomatic Nicotiana benthamiana.
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32
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Pirovano W, Miozzi L, Boetzer M, Pantaleo V. Bioinformatics approaches for viral metagenomics in plants using short RNAs: model case of study and application to a Cicer arietinum population. Front Microbiol 2015; 5:790. [PMID: 25674078 PMCID: PMC4307218 DOI: 10.3389/fmicb.2014.00790] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2014] [Accepted: 12/22/2014] [Indexed: 12/12/2022] Open
Abstract
Over the past years deep sequencing experiments have opened novel doors to reconstruct viral populations in a high-throughput and cost-effective manner. Currently a substantial number of studies have been performed which employ next generation sequencing techniques to either analyze known viruses by means of a reference-guided approach or to discover novel viruses using a de novo-based strategy. Taking advantage of the well-known Cymbidium ringspot virus we have carried out a comparison of different bioinformatics tools to reconstruct the viral genome based on 21–27 nt short (s)RNA sequencing with the aim to identify the most efficient pipeline. The same approach was applied to a population of plants constituting an ancient variety of Cicer arietinum with red seeds. Among the discovered viruses, we describe the presence of a Tobamovirus referring to the Tomato mottle mosaic virus (NC_022230), which was not yet observed on C. arietinum nor revealed in Europe and a viroid referring to Hop stunt viroid (NC_001351.1) never reported in chickpea. Notably, a reference sequence guided approach appeared the most efficient in such kind of investigation. Instead, the de novo assembly reached a non-appreciable coverage although the most prominent viral species could still be identified. Advantages and limitations of viral metagenomics analysis using sRNAs are discussed.
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Affiliation(s)
- Walter Pirovano
- Genome Analysis and Technology Department, BaseClear B. V. Leiden, Netherlands
| | - Laura Miozzi
- Institute for Sustainable Plant Protection of National Research Council Torino, Italy
| | - Marten Boetzer
- Genome Analysis and Technology Department, BaseClear B. V. Leiden, Netherlands
| | - Vitantonio Pantaleo
- Institute for Sustainable Plant Protection of National Research Council, Bari Research Unit Bari, Italy
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33
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Salicylic Acid Signaling in Plant Innate Immunity. PLANT HORMONE SIGNALING SYSTEMS IN PLANT INNATE IMMUNITY 2015. [DOI: 10.1007/978-94-017-9285-1_2] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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Abstract
Potyvirus is the largest genus of plant viruses causing significant losses in a wide range of crops. Potyviruses are aphid transmitted in a nonpersistent manner and some of them are also seed transmitted. As important pathogens, potyviruses are much more studied than other plant viruses belonging to other genera and their study covers many aspects of plant virology, such as functional characterization of viral proteins, molecular interaction with hosts and vectors, structure, taxonomy, evolution, epidemiology, and diagnosis. Biotechnological applications of potyviruses are also being explored. During this last decade, substantial advances have been made in the understanding of the molecular biology of these viruses and the functions of their various proteins. After a general presentation on the family Potyviridae and the potyviral proteins, we present an update of the knowledge on potyvirus multiplication, movement, and transmission and on potyvirus/plant compatible interactions including pathogenicity and symptom determinants. We end the review providing information on biotechnological applications of potyviruses.
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35
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Nicaise V. Crop immunity against viruses: outcomes and future challenges. FRONTIERS IN PLANT SCIENCE 2014; 5:660. [PMID: 25484888 PMCID: PMC4240047 DOI: 10.3389/fpls.2014.00660] [Citation(s) in RCA: 176] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 11/04/2014] [Indexed: 05/02/2023]
Abstract
Viruses cause epidemics on all major cultures of agronomic importance, representing a serious threat to global food security. As strict intracellular pathogens, they cannot be controlled chemically and prophylactic measures consist mainly in the destruction of infected plants and excessive pesticide applications to limit the population of vector organisms. A powerful alternative frequently employed in agriculture relies on the use of crop genetic resistances, approach that depends on mechanisms governing plant-virus interactions. Hence, knowledge related to the molecular bases of viral infections and crop resistances is key to face viral attacks in fields. Over the past 80 years, great advances have been made on our understanding of plant immunity against viruses. Although most of the known natural resistance genes have long been dominant R genes (encoding NBS-LRR proteins), a vast number of crop recessive resistance genes were cloned in the last decade, emphasizing another evolutive strategy to block viruses. In addition, the discovery of RNA interference pathways highlighted a very efficient antiviral system targeting the infectious agent at the nucleic acid level. Insidiously, plant viruses evolve and often acquire the ability to overcome the resistances employed by breeders. The development of efficient and durable resistances able to withstand the extreme genetic plasticity of viruses therefore represents a major challenge for the coming years. This review aims at describing some of the most devastating diseases caused by viruses on crops and summarizes current knowledge about plant-virus interactions, focusing on resistance mechanisms that prevent or limit viral infection in plants. In addition, I will discuss the current outcomes of the actions employed to control viral diseases in fields and the future investigations that need to be undertaken to develop sustainable broad-spectrum crop resistances against viruses.
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Affiliation(s)
- Valérie Nicaise
- Fruit Biology and Pathology, Virology Laboratory, Institut National de la Recherche Agronomique, University of BordeauxUMR 1332, Villenave d’Ornon, France
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36
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Dadami E, Dalakouras A, Zwiebel M, Krczal G, Wassenegger M. An endogene-resembling transgene is resistant to DNA methylation and systemic silencing. RNA Biol 2014; 11:934-41. [PMID: 25180820 PMCID: PMC4179966 DOI: 10.4161/rna.29623] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 06/11/2014] [Accepted: 06/17/2014] [Indexed: 11/19/2022] Open
Abstract
In plants, endogenes are less prone to RNA silencing than transgenes. While both can be efficiently targeted by small RNAs for post-transcriptional gene silencing (PTGS), generally only transgene PTGS is accompanied by transitivity, RNA-directed DNA methylation (RdDM) and systemic silencing. In order to investigate whether a transgene could mimick an endogene and thus be less susceptible to RNA silencing, we generated an intron-containing, endogene-resembling GREEN FLUORESCENT PROTEIN (GFP) transgene (GFP(endo)). Upon agroinfiltration of a hairpin GFP (hpF) construct, transgenic Nicotiana benthamiana plants harboring GFP(endo) (Nb-GFP(endo)) were susceptible to local PTGS. Yet, in the local area, PTGS was not accompanied by RdDM of the GFP(endo) coding region. Importantly, hpF-agroinfiltrated Nb-GFP(endo) plants were resistant to systemic silencing. For reasons of comparison, transgenic N. benthamiana plants (Nb-GFP(cDNA)) carrying a GFP cDNA transgene (GFP(cDNA)) were included in the analysis. HpF-agroinfiltrated Nb-GFP(cDNA) plants exhibited local PTGS and RdDM. In addition, systemic silencing was established in Nb-GFP(cDNA) plants. In agreement with previous reports using grafted scions, in systemically silenced tissue, siRNAs mapping to the 3' of GFP were predominantly detectable by Northern blot analysis. Yet, in contrast to other reports, in systemically silenced leaves, PTGS was also accompanied by dense RdDM comprising the entire GFP(cDNA) coding region. Overall, our analysis indicated that cDNA transgenes are prone to systemic PTGS and RdDM, while endogene-resembling ones are resistant to RNA silencing.
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Affiliation(s)
- Elena Dadami
- RLP AgroScience GmbH; AlPlanta-Institute for Plant Research; Neustadt, Germany
| | | | - Michele Zwiebel
- RLP AgroScience GmbH; AlPlanta-Institute for Plant Research; Neustadt, Germany
| | - Gabi Krczal
- RLP AgroScience GmbH; AlPlanta-Institute for Plant Research; Neustadt, Germany
| | - Michael Wassenegger
- RLP AgroScience GmbH; AlPlanta-Institute for Plant Research; Neustadt, Germany
- Centre for Organismal Studies (COS) Heidelberg; University of Heidelberg; Heidelberg, Germany
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37
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Agüero J, Vives MDC, Velázquez K, Pina JA, Navarro L, Moreno P, Guerri J. Effectiveness of gene silencing induced by viral vectors based on Citrus leaf blotch virus is different in Nicotiana benthamiana and citrus plants. Virology 2014; 460-461:154-64. [PMID: 25010281 DOI: 10.1016/j.virol.2014.04.017] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Revised: 02/12/2014] [Accepted: 04/12/2014] [Indexed: 11/23/2022]
Abstract
Virus induced gene silencing (VIGS) is an effective technology for gene function analysis in plants. We assessed the VIGS effectiveness in Nicotiana benthamiana and citrus plants of different Citrus leaf blotch virus (CLBV)-based vectors, using insets of the phytoene desaturase (pds) gene. While in N. benthamiana the silencing phenotype was induced only by the construct carrying a 58-nt pds hairpin, in citrus plants all the constructs induced the silencing phenotype. Differences in the generation of secondary small interfering RNAs in both species are believed to be responsible for differential host-species effects. The ability of CLBV-based vectors to silence different endogenous citrus genes was further confirmed. Since CLBV-based vectors are known to be stable and induce VIGS in successive flushes for several months, these vectors provide an important genomic tool and it is expected that they will be useful to analyze gene function by reverse genetics in the long-lived citrus plants.
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Affiliation(s)
- Jesus Agüero
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - María del Carmen Vives
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - Karelia Velázquez
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - José Antonio Pina
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - Luis Navarro
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - Pedro Moreno
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain
| | - Jose Guerri
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias (IVIA), Ctra. Moncada-Náquera Km. 4.5, Moncada, 46113 Valencia, Spain.
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38
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Senthil-Kumar M, Mysore KS. Tobacco rattle virus-based virus-induced gene silencing in Nicotiana benthamiana. Nat Protoc 2014; 9:1549-62. [PMID: 24901739 DOI: 10.1038/nprot.2014.092] [Citation(s) in RCA: 201] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) is widely used in various plant species to downregulate the expression of a target plant gene. TRV is a bipartite, positive-strand RNA virus with the TRV1 and TRV2 genomes. To induce post-transcriptional gene silencing (PTGS), the TRV2 genome is genetically modified to carry a fragment of the target gene and delivered into the plant (along with the TRV1 genome) by agroinoculation. TRV1- and TRV2-carrying Agrobacterium strains are then co-inoculated into 3-week-old plant leaves by one of three methods: a needleless syringe, the agrodrench method or by pricking with a toothpick. Target gene silencing occurs in the newly developed noninoculated leaves within 2-3 weeks of TRV inoculation. The TRV-VIGS protocol described here takes only 4 weeks to implement, and it is faster and easier to perform than other gene silencing techniques that are currently available. Although we use Nicotiana benthamiana as an example, the protocol is adaptable to other plant species.
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Affiliation(s)
- Muthappa Senthil-Kumar
- 1] Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma, USA. [2] National Institute of Plant Genome Research, New Delhi, India
| | - Kirankumar S Mysore
- Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma, USA
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39
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Wang N, Zhang D, Wang Z, Xun H, Ma J, Wang H, Huang W, Liu Y, Lin X, Li N, Ou X, Zhang C, Wang MB, Liu B. Mutation of the RDR1 gene caused genome-wide changes in gene expression, regional variation in small RNA clusters and localized alteration in DNA methylation in rice. BMC PLANT BIOLOGY 2014; 14:177. [PMID: 24980094 PMCID: PMC4083042 DOI: 10.1186/1471-2229-14-177] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 06/03/2014] [Indexed: 05/08/2023]
Abstract
BACKGROUND Endogenous small (sm) RNAs (primarily si- and miRNAs) are important trans/cis-acting regulators involved in diverse cellular functions. In plants, the RNA-dependent RNA polymerases (RDRs) are essential for smRNA biogenesis. It has been established that RDR2 is involved in the 24 nt siRNA-dependent RNA-directed DNA methylation (RdDM) pathway. Recent studies have suggested that RDR1 is involved in a second RdDM pathway that relies mostly on 21 nt smRNAs and functions to silence a subset of genomic loci that are usually refractory to the normal RdDM pathway in Arabidopsis. Whether and to what extent the homologs of RDR1 may have similar functions in other plants remained unknown. RESULTS We characterized a loss-of-function mutant (Osrdr1) of the OsRDR1 gene in rice (Oryza sativa L.) derived from a retrotransposon Tos17 insertion. Microarray analysis identified 1,175 differentially expressed genes (5.2% of all expressed genes in the shoot-tip tissue of rice) between Osrdr1 and WT, of which 896 and 279 genes were up- and down-regulated, respectively, in Osrdr1. smRNA sequencing revealed regional alterations in smRNA clusters across the rice genome. Some of the regions with altered smRNA clusters were associated with changes in DNA methylation. In addition, altered expression of several miRNAs was detected in Osrdr1, and at least some of which were associated with altered expression of predicted miRNA target genes. Despite these changes, no phenotypic difference was identified in Osrdr1 relative to WT under normal condition; however, ephemeral phenotypic fluctuations occurred under some abiotic stress conditions. CONCLUSIONS Our results showed that OsRDR1 plays a role in regulating a substantial number of endogenous genes with diverse functions in rice through smRNA-mediated pathways involving DNA methylation, and which participates in abiotic stress response.
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Affiliation(s)
- Ningning Wang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
- Faculty of Agronomy, Jilin Agricultural University, Changchun 130118, China
- Commonwealth Scientific and Industrial Research Organisation Plant Industry, Canberra, Australian Capital Territory 2601, Australia
| | - Di Zhang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Zhenhui Wang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Hongwei Xun
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Jian Ma
- Faculty of Agronomy, Jilin Agricultural University, Changchun 130118, China
| | - Hui Wang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Wei Huang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Ying Liu
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Xiuyun Lin
- Jilin Academy of Agricultural Sciences, Changchun 130033, China
| | - Ning Li
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Xiufang Ou
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
| | - Chunyu Zhang
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
- School of Food Production Technology and Biotechnology, Changchun Vocational Institute of Technology, Changchun, China
| | - Ming-Bo Wang
- Commonwealth Scientific and Industrial Research Organisation Plant Industry, Canberra, Australian Capital Territory 2601, Australia
| | - Bao Liu
- Key Laboratory of Molecular Epigenetics of Ministry of Education (MOE), Northeast Normal University, Changchun 130024, China
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Liou MR, Huang YW, Hu CC, Lin NS, Hsu YH. A dual gene-silencing vector system for monocot and dicot plants. PLANT BIOTECHNOLOGY JOURNAL 2014; 12:330-43. [PMID: 24283212 DOI: 10.1111/pbi.12140] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 09/18/2013] [Accepted: 10/14/2013] [Indexed: 05/16/2023]
Abstract
Plant virus-based gene-silencing vectors have been extensively and successfully used to elucidate functional genomics in plants. However, only limited virus-induced gene-silencing (VIGS) vectors can be used in both monocot and dicot plants. Here, we established a dual gene-silencing vector system based on Bamboo mosaic virus (BaMV) and its satellite RNA (satBaMV). Both BaMV and satBaMV vectors could effectively silence endogenous genes in Nicotiana benthamiana and Brachypodium distachyon. The satBaMV vector could also silence the green fluorescent protein (GFP) transgene in GFP transgenic N. benthamiana. GFP transgenic plants co-agro-inoculated with BaMV and satBaMV vectors carrying sulphur and GFP genes, respectively, could simultaneously silence both genes. Moreover, the silenced plants could still survive with the silencing of genes essential for plant development such as heat-shock protein 90 (Hsp90) and Hsp70. In addition, the satBaMV- but not BaMV-based vector could enhance gene-silencing efficiency in newly emerging leaves of N. benthamiana deficient in RNA-dependant RNA polymerase 6. The dual gene-silencing vector system of BaMV and satBaMV provides a novel tool for comparative functional studies in monocot and dicot plants.
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Affiliation(s)
- Ming-Ru Liou
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan; Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
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Li F, Huang C, Li Z, Zhou X. Suppression of RNA silencing by a plant DNA virus satellite requires a host calmodulin-like protein to repress RDR6 expression. PLoS Pathog 2014; 10:e1003921. [PMID: 24516387 PMCID: PMC3916407 DOI: 10.1371/journal.ppat.1003921] [Citation(s) in RCA: 136] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Accepted: 12/24/2013] [Indexed: 11/19/2022] Open
Abstract
In plants, RNA silencing plays a key role in antiviral defense. To counteract host defense, plant viruses encode viral suppressors of RNA silencing (VSRs) that target different effector molecules in the RNA silencing pathway. Evidence has shown that plants also encode endogenous suppressors of RNA silencing (ESRs) that function in proper regulation of RNA silencing. The possibility that these cellular proteins can be subverted by viruses to thwart host defense is intriguing but has not been fully explored. Here we report that the Nicotiana benthamiana calmodulin-like protein Nbrgs-CaM is required for the functions of the VSR βC1, the sole protein encoded by the DNA satellite associated with the geminivirus Tomato yellow leaf curl China virus (TYLCCNV). Nbrgs-CaM expression is up-regulated by the βC1. Transgenic plants over-expressing Nbrgs-CaM displayed developmental abnormities reminiscent of βC1-associated morphological alterations. Nbrgs-CaM suppressed RNA silencing in an Agrobacterium infiltration assay and, when over-expressed, blocked TYLCCNV-induced gene silencing. Genetic evidence showed that Nbrgs-CaM mediated the βC1 functions in silencing suppression and symptom modulation, and was required for efficient virus infection. Moreover, the tobacco and tomato orthologs of Nbrgs-CaM also possessed ESR activity, and were induced by betasatellite to promote virus infection in these Solanaceae hosts. We further demonstrated that βC1-induced Nbrgs-CaM suppressed the production of secondary siRNAs, likely through repressing RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) expression. RDR6-deficient N. benthamiana plants were defective in antiviral response and were hypersensitive to TYLCCNV infection. More significantly, TYLCCNV could overcome host range restrictions to infect Arabidopsis thaliana when the plants carried a RDR6 mutation. These findings demonstrate a distinct mechanism of VSR for suppressing PTGS through usurpation of a host ESR, and highlight an essential role for RDR6 in RNA silencing defense response against geminivirus infection.
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Affiliation(s)
- Fangfang Li
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, China
| | - Changjun Huang
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, China
| | - Zhenghe Li
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, China
| | - Xueping Zhou
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou, China
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
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42
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Boccara M, Sarazin A, Thiébeauld O, Jay F, Voinnet O, Navarro L, Colot V. The Arabidopsis miR472-RDR6 silencing pathway modulates PAMP- and effector-triggered immunity through the post-transcriptional control of disease resistance genes. PLoS Pathog 2014; 10:e1003883. [PMID: 24453975 PMCID: PMC3894208 DOI: 10.1371/journal.ppat.1003883] [Citation(s) in RCA: 166] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Accepted: 11/28/2013] [Indexed: 11/18/2022] Open
Abstract
RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) is a key RNA silencing factor initially characterized in transgene silencing and virus resistance. This enzyme also contributes to the biosynthesis of endogenous short interfering RNAs (siRNAs) from non-coding RNAs, transposable elements and protein-coding transcripts. One class of protein-coding transcripts that have recently emerged as major sources of RDR6-dependent siRNAs are nucleotide-binding leucine-rich repeat (NB-LRR) proteins, a family of immune-receptors that perceive specific pathogen effector proteins and mount Effector-Triggered Immunity (ETI). Nevertheless, the dynamic post-transcriptional control of NB-LRR transcripts during the plant immune response and the functional relevance of NB-LRRs in signaling events triggered by Pathogen-Associated Molecular Patterns (PAMPs) remain elusive. Here, we show that PTI is constitutive and sensitized in the Arabidopsis rdr6 loss-of-function mutant, implicating RDR6 as a novel negative regulator of PTI. Accordingly, rdr6 mutant exhibits enhanced basal resistance towards a virulent Pseudomonas syringae strain. We further provide evidence that dozens of CC-NB-LRRs (CNLs), including the functionally characterized RPS5 gene, are post-transcriptionally controlled by RDR6 both constitutively and during PTI. These CNL transcripts are also regulated by the Arabidopsis microRNA miR472 and knock-down of this miRNA recapitulates the PTI and basal resistance phenotypes observed in the rdr6 mutant background. Furthermore, both miR472 and rdr6 mutants were more resistant to Pto DC3000 expressing AvrPphB, a bacterial effector recognized by the disease resistance protein RPS5, whereas transgenic plants overexpressing miR472 were more susceptible to this bacterial strain. Finally, we show that the enhanced basal and RPS5-mediated resistance phenotypes observed in the rdr6 mutant are dependent on the proper chaperoning of NB-LRR proteins, and might therefore be due to the enhanced accumulation of CNL proteins whose cognate mRNAs are no longer controlled by RDR6-dependent siRNAs. Altogether, this study supports a model whereby the miR472- and RDR6-mediated silencing pathway represents a key regulatory checkpoint modulating both PTI and ETI responses through the post-transcriptional control of disease resistance genes. Virus resistance relies in some plant-viral interactions on the RNA-DEPENDANT RNA POLYMERASE 6 (RDR6), a major actor of RNA silencing that acts at the post-transcriptional level. Here, we demonstrate that RDR6 also plays a role in basal defense and race-specific resistance. RDR6 and the microRNA miR472, which targets the mRNAs of disease resistance genes of coiled-coil nucleotide-binding leucine-rich-repeats family (e.g. RPS5), act in cooperation to control post-transcriptionally these immune receptors. Induction of these resistance genes is primed in rdr6- and miR472-elicited mutants and this effect is associated with an enhanced basal and race-specific immunity in these backgrounds.
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Affiliation(s)
- Martine Boccara
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
- Université Pierre et Marie Curie, Paris, France
- * E-mail: (MB); (LN); (VC)
| | - Alexis Sarazin
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
| | - Odon Thiébeauld
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
| | - Florence Jay
- ETH Zurich, Department of Biology, Chair of RNA biology, Zurich, Switzerland
| | - Olivier Voinnet
- ETH Zurich, Department of Biology, Chair of RNA biology, Zurich, Switzerland
| | - Lionel Navarro
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
- * E-mail: (MB); (LN); (VC)
| | - Vincent Colot
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
- * E-mail: (MB); (LN); (VC)
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43
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Boccara M, Sarazin A, Thiébeauld O, Jay F, Voinnet O, Navarro L, Colot V. The Arabidopsis miR472-RDR6 silencing pathway modulates PAMP- and effector-triggered immunity through the post-transcriptional control of disease resistance genes. PLoS Pathog 2014. [PMID: 24453975 DOI: 10.1371/journal.ppat.100388] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2023] Open
Abstract
RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) is a key RNA silencing factor initially characterized in transgene silencing and virus resistance. This enzyme also contributes to the biosynthesis of endogenous short interfering RNAs (siRNAs) from non-coding RNAs, transposable elements and protein-coding transcripts. One class of protein-coding transcripts that have recently emerged as major sources of RDR6-dependent siRNAs are nucleotide-binding leucine-rich repeat (NB-LRR) proteins, a family of immune-receptors that perceive specific pathogen effector proteins and mount Effector-Triggered Immunity (ETI). Nevertheless, the dynamic post-transcriptional control of NB-LRR transcripts during the plant immune response and the functional relevance of NB-LRRs in signaling events triggered by Pathogen-Associated Molecular Patterns (PAMPs) remain elusive. Here, we show that PTI is constitutive and sensitized in the Arabidopsis rdr6 loss-of-function mutant, implicating RDR6 as a novel negative regulator of PTI. Accordingly, rdr6 mutant exhibits enhanced basal resistance towards a virulent Pseudomonas syringae strain. We further provide evidence that dozens of CC-NB-LRRs (CNLs), including the functionally characterized RPS5 gene, are post-transcriptionally controlled by RDR6 both constitutively and during PTI. These CNL transcripts are also regulated by the Arabidopsis microRNA miR472 and knock-down of this miRNA recapitulates the PTI and basal resistance phenotypes observed in the rdr6 mutant background. Furthermore, both miR472 and rdr6 mutants were more resistant to Pto DC3000 expressing AvrPphB, a bacterial effector recognized by the disease resistance protein RPS5, whereas transgenic plants overexpressing miR472 were more susceptible to this bacterial strain. Finally, we show that the enhanced basal and RPS5-mediated resistance phenotypes observed in the rdr6 mutant are dependent on the proper chaperoning of NB-LRR proteins, and might therefore be due to the enhanced accumulation of CNL proteins whose cognate mRNAs are no longer controlled by RDR6-dependent siRNAs. Altogether, this study supports a model whereby the miR472- and RDR6-mediated silencing pathway represents a key regulatory checkpoint modulating both PTI and ETI responses through the post-transcriptional control of disease resistance genes.
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Affiliation(s)
- Martine Boccara
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France ; Université Pierre et Marie Curie, Paris, France
| | - Alexis Sarazin
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
| | - Odon Thiébeauld
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
| | - Florence Jay
- ETH Zurich, Department of Biology, Chair of RNA biology, Zurich, Switzerland
| | - Olivier Voinnet
- ETH Zurich, Department of Biology, Chair of RNA biology, Zurich, Switzerland
| | - Lionel Navarro
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
| | - Vincent Colot
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Centre National de la Recherche Scientifique UMR8197, Institut National de la Santé et de la Recherche Médicale U1024, Paris, France
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Dalakouras A, Wassenegger M. Revisiting RNA-directed DNA methylation. RNA Biol 2013; 10:453-5. [PMID: 23324611 PMCID: PMC3672289 DOI: 10.4161/rna.23542] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Revised: 01/07/2013] [Accepted: 01/09/2013] [Indexed: 11/19/2022] Open
Abstract
RNA-directed DNA methylation (RdDM) involves sequence-specific guiding of the de novo methylation machinery to complementary genomic DNA by RNA molecules. It is still elusive whether guide RNAs bind directly to DNA or to nascent transcripts produced from it. Even the nature of the guide RNAs is not elucidated. RNA interference (RNAi) studies provided a link between RNAi and RdDM indicating that small interfering RNAs (siRNAs) trigger and guide cytosine methylation. The "siRNA hypothesis" is generally accepted. However, recent data demonstrated that RdDM is not always associated with the accumulation of corresponding siRNAs. RdDM triggers may differ from guide RNAs and further studies are needed to clarify if guide RNAs are small or long RNAs, if they are single or double stranded and if they target DNA or nascent transcript.
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Affiliation(s)
| | - Michael Wassenegger
- RLP AgroScience GmbH; AlPlanta-Institute for Plant Research; Neustadt, Germany
- Centre for Organismal Studies (COS) Heidelberg; University of Heidelberg; Heidelberg, Germany
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45
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Szittya G, Burgyán J. RNA Interference-Mediated Intrinsic Antiviral Immunity in Plants. Curr Top Microbiol Immunol 2013; 371:153-81. [DOI: 10.1007/978-3-642-37765-5_6] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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46
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Kawakatsu T, Wakasa Y, Yasuda H, Takaiwa F. RNA silencing induced by an artificial sequence that prevents proper transcription termination in rice. PLANT PHYSIOLOGY 2012; 160:601-12. [PMID: 22843666 PMCID: PMC3461542 DOI: 10.1104/pp.112.202689] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Posttranscriptional gene silencing (PTGS) is a sequence-specific mRNA degradation caused by small RNA, such as microRNA (miRNA) and small interfering RNA (siRNA). miRNAs are generated from MIRNA loci, whereas siRNAs originate from various sources of double-stranded RNA. In this study, an artificial RNA silencing inducible sequence (RSIS) was identified in rice (Oryza sativa). This sequence causes PTGS of 5' or 3' flanking-sequence-containing genes. Interestingly, two target genes can be simultaneously suppressed by linking a unique target sequence to either the 5' or 3' end of RSIS. Multiple gene suppression can be also achieved though a single transformation event by incorporating the multisite gateway system. Moreover, RSIS-mediated PTGS occurs in nuclei. Deep sequencing of small RNAs reveals that siRNAs are produced from RSIS-expressing cassettes and transitive siRNAs are produced from endogenous target genes. Furthermore, siRNAs are typically generated from untranscribed transgene terminator regions. The read-through transcripts from the RSIS-expression cassette were consistently observed, and most of these sequences were not polyadenylated. Collectively, this data indicates that RSIS inhibits proper transcription termination. The resulting transcripts are not polyadenylated. These transcripts containing RSIS become templates for double-stranded RNA synthesis in nuclei. This is followed by siRNA production and target degradation of target genes.
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47
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Liu D, Shi L, Han C, Yu J, Li D, Zhang Y. Validation of reference genes for gene expression studies in virus-infected Nicotiana benthamiana using quantitative real-time PCR. PLoS One 2012; 7:e46451. [PMID: 23029521 PMCID: PMC3460881 DOI: 10.1371/journal.pone.0046451] [Citation(s) in RCA: 242] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 08/30/2012] [Indexed: 02/04/2023] Open
Abstract
Nicotiana benthamiana is the most widely-used experimental host in plant virology. The recent release of the draft genome sequence for N. benthamiana consolidates its role as a model for plant-pathogen interactions. Quantitative real-time PCR (qPCR) is commonly employed for quantitative gene expression analysis. For valid qPCR analysis, accurate normalisation of gene expression against an appropriate internal control is required. Yet there has been little systematic investigation of reference gene stability in N. benthamiana under conditions of viral infections. In this study, the expression profiles of 16 commonly used housekeeping genes (GAPDH, 18S, EF1α, SAMD, L23, UK, PP2A, APR, UBI3, SAND, ACT, TUB, GBP, F-BOX, PPR and TIP41) were determined in N. benthamiana and those with acceptable expression levels were further selected for transcript stability analysis by qPCR of complementary DNA prepared from N. benthamiana leaf tissue infected with one of five RNA plant viruses (Tobacco necrosis virus A, Beet black scorch virus, Beet necrotic yellow vein virus, Barley stripe mosaic virus and Potato virus X). Gene stability was analysed in parallel by three commonly-used dedicated algorithms: geNorm, NormFinder and BestKeeper. Statistical analysis revealed that the PP2A, F-BOX and L23 genes were the most stable overall, and that the combination of these three genes was sufficient for accurate normalisation. In addition, the suitability of PP2A, F-BOX and L23 as reference genes was illustrated by expression-level analysis of AGO2 and RdR6 in virus-infected N. benthamiana leaves. This is the first study to systematically examine and evaluate the stability of different reference genes in N. benthamiana. Our results not only provide researchers studying these viruses a shortlist of potential housekeeping genes to use as normalisers for qPCR experiments, but should also guide the selection of appropriate reference genes for gene expression studies of N. benthamiana under other biotic and abiotic stress conditions.
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Affiliation(s)
- Deshui Liu
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Lindan Shi
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Chenggui Han
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Jialin Yu
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Dawei Li
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
| | - Yongliang Zhang
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing, China
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Yoon JY, Han KS, Park HY, Choi SK. Comparative analysis of RNA silencing suppression activities between viral suppressors and an endogenous plant RNA-dependent RNA polymerase. Virus Genes 2012; 44:495-504. [PMID: 22354861 DOI: 10.1007/s11262-012-0725-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2011] [Accepted: 02/07/2012] [Indexed: 10/28/2022]
Abstract
RNA silencing is an evolutionarily conserved system that functions as an antiviral mechanism in eukaryotes, including higher plants. To counteract this, several plant viruses express silencing suppressors that inhibit RNA silencing in host plants. Here, we show that both 2b protein from peanut stunt virus (PSV) and a hairpin construct (designated hp-RDR6) that silences endogenous RNA-dependent RNA polymerase 6 (RDR6) strongly suppress RNA silencing. The Agrobacterium infiltration system was used to demonstrate that both PSV 2b and hp-RDR6 suppressed local RNA silencing as strongly as helper component (HC-Pro) from potato virus Y (PVY) and P19 from tomato bush stunt virus (TBSV). The 2b protein from PSV eliminated the small-interfering RNAs (siRNAs) associated with RNA silencing and prevented systemic silencing, similar to 2b protein from cucumber mosaic virus (CMV). On the other hand, hp-RDR6 suppressed RNA silencing by inhibiting the generation of secondary siRNAs. The small coat protein (SCP) of squash mosaic virus (SqMV) also displayed weak suppression activity of RNA silencing. Agrobacterium-mediated gene transfer was used to investigate whether viral silencing suppressors or hp-RDR6 enhanced accumulations of green fluorescence protein (GFP) and β-glucuronidase (GUS) as markers of expression in leaf tissues of Nicotina benthamiana. Expression of both GFP and GUS was significantly enhanced in the presence of PSV 2b or CMV 2b, compared to no suppression or the weak SqMV SCP suppressor. Co-expression with hp-RDR6 also significantly increased the expression of GFP and GUS to levels similar to those induced by PVY HC-Pro and TBSV P19.
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Affiliation(s)
- Ju-Yeon Yoon
- Department of Horticulture and Landscape, Seoul Women's University, Seoul, 139-774, Republic of Korea
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49
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Huang C, Qian Y, Li Z, Zhou X. Virus-induced gene silencing and its application in plant functional genomics. SCIENCE CHINA-LIFE SCIENCES 2012; 55:99-108. [PMID: 22415680 DOI: 10.1007/s11427-012-4280-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2011] [Accepted: 12/13/2011] [Indexed: 12/13/2022]
Abstract
Virus-induced gene silencing is regarded as a powerful and efficient tool for the analysis of gene function in plants because it is simple, rapid and transformation-free. It has been used to perform both forward and reverse genetics to identify plant functional genes. Many viruses have been developed into virus-induced gene silencing vectors and gene functions involved in development, biotic and abiotic stresses, metabolism, and cellular signaling have been reported. In this review, we discuss the development and application of virus-induced gene silencing in plant functional genomics.
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Affiliation(s)
- Changjun Huang
- State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China
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50
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Characterization and functional analysis of GhRDR6, a novel RDR6 gene from cotton (Gossypium hirsutum L.). Biosci Rep 2012; 32:139-51. [PMID: 21679158 DOI: 10.1042/bsr20100086] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
RDR6 (RNA-dependent RNA polymerase 6) is not only involved in virus resistance but also plays an important role in natural plant development. In the present study, a novel RDR gene, named GhRDR6 (Gossypium hirsutum RDR6), was isolated from cotton (G. hirsutum L.). Alignment and evolutionary relationship analyses showed that GhRDR6 was more closely related to RDR6 than to other RDRs. Expression analysis indicated that this single-copy gene is constitutively expressed in the roots, stems and leaves. Semi-quantitative RT-PCR (reverse transcription-PCR) showed that GhRDR6 was up-regulated by the application of various phytohormones, including MeJA [methyl JA (jasmonate)], ABA (abscisic acid), JA, α-naphthylacetic acid, gibberellins and ET (ethylene). In addition, GhRDR6 expression increased in response to wounding, cold (4°C) and NaCl treatments, but not by drought. Furthermore, overexpression of GhRDR6 in transgenic Nicotiana benthamiana plants resulted in root lengths longer than the wide-type during the seeding stage. Interestingly, the GhRDR6-overexpressing plants displayed reduced tolerance to oxidative damage, resulting in reduced ABA-sensitivity, but they tolerated freezing. Moreover, resistance to potato virus Y was enhanced in transgenic N. benthamiana plants. These results suggest that GhRDR6 may play an important role in plant defence responses and a pivotal role in plant development.
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