53 research outputs found
Viral silencing suppressors: Tools forged to fine-tune host-pathogen coexistence
RNA silencing is a homology-dependent gene inactivation mechanism that regulates a wide range of biological processes including antiviral defense. To deal with host antiviral responses viruses evolved mechanisms to avoid or counteract this, most notably through expression of viral suppressors of RNA silencing. Besides working as silencing suppressors, these proteins may also fulfill other functions during infection. In many cases the interplay between the suppressor function and other “unrelated” functions remains elusive. We will present host factors implicated in antiviral pathways and summarize the current status of knowledge about the diverse viral suppressors’ strategies acting at various steps of antiviral silencing in plants. Besides, we will consider the multi-functionality of these versatile proteins and related biochemical processes in which they may be involved in fine-tuning the plant-virus interaction. Finally, we will present the current applications and discuss perspectives of the use of these proteins in molecular biology and biotechnology
Poszt-transzkripcionális gĂ©ncsendesĂtĂ©s Ă©s szupressziĂł molekuláris mechanizmusának feltárása növĂ©nyekben = Unraveling the mechanism of Post-transcriptional gene silencing and suppression in plants
Az RNS silencing, egy gĂ©ninaktiváciĂłs mechanizmus, amely szinte az összes eukariĂłta szervezetben működik, Ă©s magába foglalja az állati RNS interferencia Ă©s a növĂ©nyi poszt-ranszkripcionális gĂ©ncsendesĂtĂ©s (PTGS) jelensĂ©gĂ©t. A növĂ©nyekben a PTGS mint antivirális mechanizmus is működik. Kutatásaink folyamán feltártuk, hogy a vĂrus RNS erĹ‘s másodlagos szerkezettel bĂrĂł rĂ©szei aktiválják a PTGS alapĂş antivirális mechanizmust oly mĂłdon, hogy a DICER nevezetű RNAse III tĂpusĂş enzim kis 21-26 nukleotid hosszĂş RNS molekulákká, Ăşn. siRNS-ekkĂ© darabolják a másodlagos szerkezettel bĂrĂł vĂrus RNS szakaszokat. A vĂrus fertĹ‘zte növĂ©nyekben felhalmozĂłdĂł siRNS-ek beĂ©pĂĽlnek a PTGS másik effector komplexebe a RISC-be amely vĂrus specfikus siRNS-ek miatt specifikusan gátolja a vĂrus RNS kifejezĹ‘dĂ©sĂ©t. Igazoltuk, hogy ez a gátlás a vĂrus genom specifikus vágásával megy vĂ©gbe. A vĂrusok az evolĂşciĂł során silencing szupresszor fehĂ©rjĂ©k termelĂ©sĂ©vel válaszoltak a növĂ©nyek antivirális reakciĂłjára. LaboratĂłriumunkban a világon elĹ‘ször sikerĂĽlt feltárnunk egy ilyen silencing szupresszor fehĂ©rje (Cymbidium ringspot vĂrus kĂłdolta p19 fehĂ©rje) kristályszerkezetĂ©t Ă©s molekuláris működĂ©sĂ©t. MegállapĂtottuk, hogy a p19 szupresszor fehĂ©rje a siRNS-ek megkötĂ©sĂ©vel gátolja az antivirális RISC felĂ©pĂĽlĂ©sĂ©t, Ăgy a PTGS alapĂş antivirális választ. Igazoltuk továbbá, hogy ez a molekuláris mechanizmus altalánosan elterjedt a növĂ©nyi vĂrus kĂłdolta silencing szupresszor fehĂ©rjĂ©k működĂ©sĂ©ben. | RNA silencing is conserved in a broad range of eukaryotes and includes the phenomena of RNA interference in animals and posttranscriptional gene silencing (PTGS) in plants. In higher plants, PTGS acts as an antiviral system, and we have explored that antiviral PTGS is induced by viral dsRNAs or structured single-stranded RNAs (ssRNAs) that are processed into small interfering RNAs (siRNAs) by RNase III-like enzymes such as DICER. These virus specific siRNAs than guide the sequences pecific degradation of target viral RNAs by the RNA-induced silencing complex (RISC). We also showed that antiviral RISC, which programmed by the virus specific siRNAs mediates the cleavage of a target viral RNA when there is perfect or nearly perfect base pairing between the target. To counteract an antiviral RNA silencing response, plant viruses evolved and express silencing suppressor proteins. At the first time we explored the structure and molecular bases of a silencing suppressor protein. We have shown that the 19 kDa protein (p19) of Cymbidium ringspot virus is a systemic silencing suppressor that prevents the assembly of antiviral RISC complexis by binding and sequestering of siRNAs, thus inhibiting the PTGS based antiviral response. Moreover we also confirmed that sequestering of siRNA is a common strategy of silencing suppressor proteins, encoded by plant viruses
NövĂ©nyvĂrusok replikáciĂłjában, a tĂĽnet kialakulásában Ă©s a növĂ©ny vĂ©dekezĂ©si rendszerĂ©ben szerepet játszĂł gazdagĂ©nek azonosĂtása Ă©s vizsgálata = Identification and analyses of altered patterns of gene expression in compatible host elicited by plant virus infection
Az poszt-transzkripcionális gĂ©n csendesĂtĂ©s (PTGS) egy hatĂ©kony antivirális vĂ©dekezĂ©si rendszer növĂ©nyekben. Adataink azt mutatták, hogy amĂg a vad tĂpusĂş vĂrus (CymRSV) az egĂ©sz növĂ©nyt megfertĹ‘zi addig a p19 (a vĂrus PTGS szuppresszor fehĂ©rjĂ©je) deficiens vĂrus felhalmozĂłdása csak az erekre Ă©s azok környĂ©kĂ©re korlátozĂłdik. Ezek az eredmĂ©nyek arra utaltak, hogy a p19 kĂ©pes megakadályozni a PTGS mobil szignál által kiváltott aktiválĂłdását a fertĹ‘zĂ©si front elĹ‘tt, elĹ‘idĂ©zve a növĂ©ny általános fertĹ‘zöttsĂ©gĂ©t. Továbbiakban, azonosĂtottuk a PTGS alapvetĹ‘ szerepĂ©t a DI RNS mediálta tĂĽnet csökkentĂ©sben. Adataink megmutatták a PTGS asszociált 21nt siRNS-sek szerepĂ©t a szisztemikus szignalizáciĂłs esemĂ©nyekben. AzonosĂtottuk a DI RNS-ek 5' vĂ©gi szakaszát mint a tĂĽnet mĂłdosĂtásban szerepet játszĂł legfontosabb rĂ©giĂłt. LĂ©trehoztunk egy Arabidopsis protoplaszton alapulĂł szinkronizált infekciĂłs rendszert Ă©s azonosĂtottunk egy endogĂ©n gĂ©nt, amely teljes "shut off"-t mutat vĂrus fertĹ‘zött növĂ©nyben. MĂłdisĂtott LNA oligonukleotidok felhasználásával lĂ©trehoztunk egy olyan Ă©rzĂ©keny kis RNS detektálási rendszert, amely lehetĹ‘vĂ© teszi a vĂrus ertĹ‘zĂ©sben szerepet játszĂł miRNS-ek kimutatását mind northern blot analĂzissel mind in situ hibridizáciĂłval. | In plants post-transcriptional gene silencing (PTGS) is an ancient and effective defense mechanism against virus infection. We showed that in contrast to the uniform accumulation of CymRSV throughout systemically infected leaves, the presence of p19 (PTGS suppressor of the virus) deficient virus was confined to and around the vascular bundles. These results suggest that the role of p19 is to prevent the onset of mobile signal induced systemic PTGS ahead the virus infection front leading to generalized infection. We also showed that the activation of PTGS plays a pivotal role in DI RNA-mediated interference. Our data identified the pivotal role of 21 nt siRNAs in PTGS signaling. In addition we identified a 5' proximal sequence element of DI RNAs as the most important symptom determinant region. We established a Arabidopsis protoplast based synchronized infection system and identified an endogenous gene showing complete shut off in virus infected plants. Moreover, we enhanced the sensitivity of detecting mature microRNAs by LNA modified oligonucleotides probes, which may open the way of northern blot and in situ detection of miRNAs playing important in symptom development
Az RNS silencing mechanizmusának vizsgálata állati és növényi modelleken = Mechanism of RNS silencing in animal and plant model organism
A Cymbidium ringspot vĂrussal fertĹ‘zött növĂ©nyekbĹ‘l származĂł kis RNS-ek analĂzise során azt találtuk, hogy a virális kis RNS-ek a genom kitĂĽntetett helyeirĹ‘l keletkeznek Ă©s a a virális kis RNS-ek 80%-a a pozitĂv, 20%-a a negatĂv szálrĂłl kĂ©pzĹ‘dik. Ez az arány megegyezik a genomi RNS-ek szálarányával. EredmĂ©nyeinkbĹ‘l az következik, hogy a virális kis RNS-ek nem a virus ds replikatĂv intermedierjĂ©rĹ‘l, hanem az egyszálĂş genomi RNS-ek másodlagos szerkezettel rendelkezĹ‘ rĂ©giĂłirĂłl keletkeznek. Az RNS silencing szupresszorokkal vĂ©gzett munkánk alapján megállapĂtottuk, hogy a vizsgált virális szupresszorok mind a növĂ©nyi, mind az állati rendszerekben a kis RNS-ek megkötĂ©sĂ©vel gátolják a RISC komplexek, ezáltal a si- Ă©s miRNS indukálta RNS silencing kialakulását. Mivel az általunk vizsgált vĂrusok taxonĂłmiailag kĂĽlönbözĹ‘ családokba sorolhatĂłk, ezĂ©rt azt a következtetĂ©s is levonhatjuk, hogy a siRNS kötĂ©sen alapulĂł RNS silencing gátlás egy szĂ©leskörűen elterjedt RNS silencing szupressziĂłs stratĂ©gia. JĂłl jellemzett kis RNS kötĹ‘ RNS silencing szupresszorral rendelkezĹ‘ vĂrusok hatását vizsgáltuk a a kis RNS-ek 3 vesszĹ‘ vĂ©g metiláciĂłjára. EredmĂ©nyeink azt mutatják, hogy a TEV HCPro hatĂ©konyan, mĂg a CIRV p19 kevĂ©ssĂ© gátolja meg a virális siRNS-ek Ă©s bizonyos endogĂ©n miRNS-ek 3 vesszĹ‘ vĂ©gĂ©nek metiláciĂłját. Sejtfrakcionálásos eredmĂ©nyeink alapján feltĂ©telezhetjĂĽk, hogy a kis RNS-ek metiláciĂłja nemcsak a sejtmagban, hanem a citoplazmában is bekövetkezhet. | A survey of virus-specific siRNAs characterized by a sequence analysis of siRNAs from plants infected with Cymbidium ringspot virus showed that viral siRNA sequences have a nonrandom distribution along the length of the viral genome, suggesting that viral siRNAs derived from highly structured regions of the single stranded viral genome, rather than the ds replicative intermedier. Analyzing several silencing suppressors representing different families of viruses showed that each inhibit the intermediate step of RNA silencing via binding to siRNAs, although the molecular features required for duplex siRNA binding differ among these proteins. None of the suppressors affected the activity of preassembled RISC complexes. In contrast, each suppressor uniformly inhibited the siRNA-initiated RISC assembly pathway by preventing RNA silencing initiator complex formation. We investigated the 3' modification of silencing-related small RNAs in plants infected with viruses expressing small RNA silencing suppressors. We found that CIRV had only a slight effect on viral siRNA 3' modification, but TEV significantly inhibited the 3' modification of si/miRNAs. This suggests that the 3' modification of viral siRNAs occurs in the cytoplasm, though miRNA 3' modification likely takes place in the nucleus as well
Az RNS silencing szerepe, mechanizmusa a vĂrus gazda kölcsönhatásban = The role and the mechanism of RNA silencing in the plant virus interplay
Az RNS silencing, egy gĂ©ninaktiváciĂłs mechanizmus, amely szinte az összes eukariĂłta szervezetben működik. Kutatásaink során feltártuk a Cymbidium ringspot vĂrus genomrĂłl kĂ©zĹ‘dĹ‘ small interferálĂł (si) RNS eredetĂ©t nagy hatĂ©konyságĂş 454 (Life Science) Ă©s Soplexa (illumina) szekvenalĂł rendszerek alkalmazásával. A vĂrus genomrĂłl származĂł kis RNS-eket rátĂ©rkĂ©peztĂĽk a vĂrus genomjára, amely alapján "forrĂł pontokat" tudtunk azonosĂtani. Igazoltuk,hogy virus siRNS-ek tĂşlnyomĂł töbsĂ©ge a virus pozitĂv szálárĂłl származik, Ă©s 21-22 nukleotid (nt) hosszĂş. MegállapĂtottuk, hogy vĂrus siRNS-ekkel töltött RISC (RNA Induced Silencing Complex) komplexek szekvenciaspecifikusan hasĂtják a vĂrus genomot. Számos silencing szupresszor fehĂ©rje (p19, HC-Pro, Ă©s p122) rĂ©szletes analĂzisĂ©vel igazoltuk, hogy a növĂ©ny antivirális válaszát, a vĂrus kĂłdolta silencing szupresszorok hatĂ©konyan gátolják. BizonyĂtottuk, hogy a siRNS-ek specifikus kötĂ©se Ă©s inaktiválása a legelterjedtebb stratĂ©gia a silencing szupresszor fehĂ©rjĂ©k között. Feltártuk, hogy a silencing szuppresszor fehĂ©rjĂ©k egy jelentĹ‘s csoportja gátolja növĂ©nyek endogĂ©n siRNS Ă©s miRNS biogenezisĂ©t. A silencing szupressor feherjĂ©k interakciĂłja az endogen silencing Ăştvonalakkal feltehetĹ‘en a magyarázata a vĂrus okozta tĂĽnetek kialakulásának, hiszen a szupresszor fehĂ©rjĂ©k sĂşlyosan zavarja növĂ©ny egyedfejlĹ‘dĂ©sĂ©t. | RNA silencing is a gene inactivation mechanism, which is conserved in a broad range of eukaryotes. The central players in RNA-mediated gene silencing are the small 21-24 nucleotide long RNA molecules engaged in sequence-specific interactions to inhibit gene expression. RNA silencing fulfils fundamental regulatory roles, as well as antiviral functions. We profiled viral siRNAs using two different high-throughput sequencing platforms. Both deep sequencing techniques revealed a strong bias in viral siRNAs for the positive strand of the virus and identified regions on the viral genome that produced viral siRNA in much higher abundance than other regions. We also analysed the viral RNA targeting by virus induced gene silencing in tombusvirus infected plants, and we show evidence that antiviral response is based on viral RNA cleavage by RNA-induced silencing effector complex (RISC) programmed by virus-specific siRNAs.. To counteract RNA silencing, viruses express silencing suppressors that interfere with both siRNA- and microRNA-guided silencing pathways. We used comparative approaches to analyse the molecular mechanism of suppression by three well-studied silencing suppressors. We found that silencing suppressors p19, p21 and HC-Pro each inhibit the RISC assembly. We demonstrated that these suppressors are able to interact with the endogenous silencing pathways suggesting that these interactions have an important role in the development of virus-induced symptoms
The nonstop decay and the RNA silencing systems operate cooperatively in plants
Translation-dependent mRNA quality control systems protect the protein homeostasis of eukaryotic cells by eliminating aberrant transcripts and stimulating the decay of their protein products. Although these systems are intensively studied in animals, little is known about the translation-dependent quality control systems in plants. Here, we characterize the mechanism of nonstop decay (NSD) system in Nicotiana benthamiana model plant. We show that plant NSD efficiently degrades nonstop mRNAs, which can be generated by premature polyadenylation, and stop codon-less transcripts, which are produced by endonucleolytic cleavage. We demonstrate that in plants, like in animals, Pelota, Hbs1 and SKI2 proteins are required for NSD, supporting that NSD is an ancient and conserved eukaryotic quality control system. Relevantly, we found that NSD and RNA silencing systems cooperate in plants. Plant silencing predominantly represses target mRNAs through endonucleolytic cleavage in the coding region. Here we show that NSD is required for the elimination of 5' cleavage product of mi- or siRNA-guided silencing complex when the cleavage occurs in the coding region. We also show that NSD and nonsense-mediated decay (NMD) quality control systems operate independently in plants
Distinct Effects of p19 RNA Silencing Suppressor on Small RNA Mediated Pathways in Plants
RNA silencing is one of the main defense mechanisms employed by plants to fight viruses. In change, viruses have evolved silencing suppressor proteins to neutralize antiviral silencing. Since the endogenous and antiviral functions of RNA silencing pathway rely on common components, it was suggested that viral suppressors interfere with endogenous silencing pathway contributing to viral symptom development. In this work, we aimed to understand the effects of the tombusviral p19 suppressor on endogenous and antiviral silencing during genuine virus infection. We showed that ectopically expressed p19 sequesters endogenous small RNAs (sRNAs) in the absence, but not in the presence of virus infection. Our presented data question the generalized model in which the sequestration of endogenous sRNAs by the viral suppressor contributes to the viral symptom development. We further showed that p19 preferentially binds the perfectly paired ds-viral small interfering RNAs (vsiRNAs) but does not select based on their sequence or the type of the 5’ nucleotide. Finally, co-immunoprecipitation of sRNAs with AGO1 or AGO2 from virus-infected plants revealed that p19 specifically impairs vsiRNA loading into AGO1 but not AGO2. Our findings, coupled with the fact that p19-expressing wild type Cymbidium ringspot virus (CymRSV) overcomes the Nicotiana benthamiana silencing based defense killing the host, suggest that AGO1 is the main effector of antiviral silencing in this host-virus combination
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