Differential Subnuclear Localization of RNA Strands of Opposite Polarity Derived from an Autonomously Replicating Viroid[W]

Qi, Yijun; Ding, Biao

doi:10.1105/tpc.016576

Cited by 92 publications

(96 citation statements)

References 66 publications

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“…Therefore, processing of HSVd dimeric transcripts appears to be a polarity intrinsic property, which dictates the susceptibility to and the specificity of the reactions mediated by the host enzymes. The recent finding that in infected cultured cells and plants, PSTVd (Ϫ) strands accumulate in the nucleoplasm, whereas the (ϩ) strands are localized in the nucleolus and in the nucleoplasm, provides an explanation for this different behavior and suggests that processing of the (ϩ) strands occurs in the nucleolus (28), where processing of the precursors of rRNAs and tRNAs also takes place (see ref. 57 for a review).…”

Section: Transgenic Arabidopsis Expressing Hsvd Dimeric (؊) Rnas Accumentioning

confidence: 99%

“…The resulting head-to-tail (ϩ) multimers are cleaved into unit-length strands and subsequently ligated into the final progeny of monomeric (ϩ) circular RNAs by an RNase and an RNA ligase, respectively. This asymmetric version of the rolling-circle mechanism is followed by Potato spindle tuber viroid (PSTVd) (21,22) and other members of the family Pospiviroidae, which replicate in the nucleus (23)(24)(25)(26)(27)(28). In contrast, Avocado sunblotch viroid (ASBVd) and other members of the family Avsunviroidae, which replicate in the chloroplast, follow a symmetric version in which the (Ϫ) multimers are processed to the monomeric (Ϫ) circular forms, the template for the second half of the replication cycle that is symmetric to the first (29)(30)(31)(32).…”

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confidence: 99%

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Arabidopsis thaliana has the enzymatic machinery for replicating representative viroid species of the family Pospiviroidae

Daròs

Flores

2004

Proc. Natl. Acad. Sci. U.S.A.

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Viroids, subviral noncoding RNAs, replicate, move, and incite diseases in plants. Viroids replicate through a rolling-circle mechanism in which oligomeric RNAs of one or both polarities are cleaved and ligated into the circular monomers. Attempts to transmit viroids to Arabidopsis have failed for unknown reasons. To tackle this question, Arabidopsis was transformed with cDNAs expressing dimeric (؉) transcripts of representative species of the families Pospiviroidae and Avsunviroidae, which replicate in the nucleus and the chloroplast, respectively. Correct processing to the circular (؉) monomers was always observed, demonstrating that Arabidopsis has the appropriate RNase and RNA ligase. Northern blot hybridization also revealed the multimeric (؊) RNAs of Citrus exocortis viroid and Hop stunt viroid (HSVd) of the family Pospiviroidae, but not of Avocado sunblotch viroid of the family Avsunviroidae, showing that the first RNA-RNA transcription of the rolling-circle mechanism occurs in Arabidopsis for the two nuclear viroids and that their multimeric (؊) RNAs remain unprocessed as in typical hosts. Moreover, transgenic Arabidopsis expressing HSVd dimeric (؊) transcripts accumulated the circular (؉) monomers, although at low levels, together with the unprocessed primary transcript that served as the template for the second RNA-RNA transcription. Agroinoculation of Arabidopsis with the dimeric (؉) Citrus exocortis viroid, HSVd, and Coleus blumei viroid 1 cDNAs showed that these viroids could not move to distal plant parts, in contrast with the situation observed in their experimental hosts. Therefore, deficiencies in movement or low replication appear to be the factors limiting infectivity of some viroids in Arabidopsis.S ince Arabidopsis thaliana was adopted as the model organism for higher plants, multiple tools, resources, and experimental approaches have been developed that facilitate research with this system (1). Principal among them is the availability of the complete sequence of the Arabidopsis genome (2). Research on plant viruses has also benefited from the use of such a versatile system. In particular, studies with viruses that naturally or experimentally infect Arabidopsis have led to the identification of host factors involved in their amplification (3, 4) and movement (5, 6) and in posttranscriptional gene silencing-mediated phenomena that include disease induction (7) and plant defense responses (8, 9). However, no viroid has been reported to infect Arabidopsis so far.Viroids are small, noncoding circular RNAs of 246-401 nucleotides able to replicate autonomously in certain plants (see refs. 10-12 for reviews). Despite this minimal genome, viroids, in addition to their replication, are able to direct their intracellular, intercellular, and long-distance movement (13-15) and to activate host defense mechanisms (16-18) that in some cases are insufficient to block the induction of pathogenic effects. For these functions, viroids need to interact with multiple host factors, the identification of which wou...

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Section: Transgenic Arabidopsis Expressing Hsvd Dimeric (؊) Rnas Accumentioning

confidence: 99%

mentioning

confidence: 99%

Arabidopsis thaliana has the enzymatic machinery for replicating representative viroid species of the family Pospiviroidae

Daròs

Flores

2004

Proc. Natl. Acad. Sci. U.S.A.

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“…Because srPSTVds are functional guide RNAs in RISC and because PSTVd does not have silencing suppressor activities, resistance of PSTVd replication may be simply attributed to its nuclear localization, especially its localization in the nucleolus (36,65), shielding the viroid RNA molecules from the RISC machinery that is localized in the cytoplasm. However, RNA silencing at the posttranscriptional level can occur in the nucleus in Caenorhabditis elegans (60), and silencing of nucleolar RNAs has been observed in trypanosomatids (51), although whether these occur in the plant nucleus remains to be determined.…”

Section: Vol 81 2007 Viroid Rna Serves As Substrate For Dicer-like mentioning

confidence: 99%

“…Such minus strands then serve as the replication intermediates to direct synthesis of concatemeric, linear plus strands, which are finally cleaved into monomers and circularized. While the minus strands are anchored in the nucleoplasm, the plus strands traffic into the nucleolus, presumably for processing (65).…”

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confidence: 99%

A Structured Viroid RNA Serves as a Substrate for Dicer-Like Cleavage To Produce Biologically Active Small RNAs but Is Resistant to RNA-Induced Silencing Complex-Mediated Degradation

Itaya¹,

Zhong²,

Bundschuh

et al. 2007

J Virol

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185

177

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RNA silencing is a potent means of antiviral defense in plants and animals. A hallmark of this defense response is the production of 21-to 24-nucleotide viral small RNAs via mechanisms that remain to be fully understood. Many viruses encode suppressors of RNA silencing, and some viral RNAs function directly as silencing suppressors as counterdefense. The occurrence of viroid-specific small RNAs in infected plants suggests that viroids can trigger RNA silencing in a host, raising the question of how these noncoding and unencapsidated RNAs survive cellular RNA-silencing systems. We address this question by characterizing the production of small RNAs of Potato spindle tuber viroid (srPSTVds) and investigating how PSTVd responds to RNA silencing. Our molecular and biochemical studies provide evidence that srPSTVds were derived mostly from the secondary structure of viroid RNAs. Replication of PSTVd was resistant to RNA silencing, although the srPSTVds were biologically active in guiding RNA-induced silencing complex (RISC)-mediated cleavage, as shown with a sensor system. Further analyses showed that without possessing or triggering silencing suppressor activities, the PSTVd secondary structure played a critical role in resistance to RISC-mediated cleavage. These findings support the hypothesis that some infectious RNAs may have evolved specific secondary structures as an effective means to evade RNA silencing in addition to encoding silencing suppressor activities. Our results should have important implications in further studies on RNA-based mechanisms of host-pathogen interactions and the biological constraints that shape the evolution of infectious RNA structures.A major focus of current biology is to understand how a pathogen has evolved mechanisms to achieve a balance among several interrelated activities that are crucial to establish a full infection: evading or suppressing host defense, minimizing destructive interference of host metabolism, and maximizing utilization of host factors to support replication and systemic spread. A full understanding of these mechanisms is not only necessary to build a foundation for developing technologies to combat pathogen diseases but also can provide fundamental mechanistic insights into the regulation of basic cellular processes.Recent studies have discovered small RNA-mediated gene silencing as a powerful antiviral mechanism in plants and animals (6,22,25,47,49,50,72,77,84,(87)(88)(89)98). Furthermore, small RNA-mediated gene silencing plays essential roles in regulating a wide variety of growth and development processes (4-6, 11, 13, 17, 23, 28, 42). A key mediator of RNA silencing is several classes of 21-to 24-nucleotide (nt) small RNAs.MicroRNAs (miRNAs) are produced by cleavage of hairpin RNA precursors encoded by the genome of an organism. Short interfering RNAs (siRNAs) are generated by cleavage of double-stranded RNAs (dsRNAs) that may originate from several sources, including cellular genomes, viral replication intermediates, aberrant cellular RNAs, overexpresse...

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“…Recentemente, Qi & Ding (2003b), em um elegante trabalho envolvendo hibridização , propuseram um modelo para a replicação e transporte do PSTVd no interior do núcleo da célula: (i) após a passagem do viróide do citoplasma para o núcleo, ocorre a síntese das moléculas de ambas (iii) as moléculas de polaridade positiva são transportadas as novas moléculas (positivas) retornam ao nucleoplasma e em seguida passam ao citoplasma para serem transportadas célula-a-célula. Assim, como já demonstrado para outros RNAs (Lewis & Tollervey, 2000), o nucléolo deve ser o sítio de processamento dos membros da família , os quais devem conter "motivos" para a localização e transporte para esta organela (Qi & Ding, 2003a).…”

Section: Fig 1 -Aunclassified

Viróides e virusóides: relíquias do mundo de RNA

et al. 2006

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RESUMOAté meados do século XX, os vírus eram considerados os representantes mais simples da escala biológica. A descoberta dos RNAs satélites e dos viróides por volta de 1970 foi surpreendente, pois comprovou-se a existência de uma nova classe de moléculas auto-replicativas ainda mais simples, denominada agentes sub-virais. Há indícios de que os viróides e virusóides (que formam uma classe de RNAs satélites), teriam feito parte do "Mundo de RNA" (que precedeu o mundo atual baseado no DNA e proteínas), podendo ser considerados fósseis moleculares dessa era antiga. A simplicidade desses agentes sub-virais e o fato de que a molécula de RNA deve interagir diretamente com fatores do hospedeiro para o desenvolvimento do seu ciclo infeccioso colocam esses patógenos como um modelo para o estudo de processos metabólicos celulares. Nos últimos anos, tem-se observado um volume grande de publicações visando elucidar aspectos da interação viróide/hospedeiro, como os mecanismos da patogênese, movimento dos viróides nas plantas hospedeiras, silenciamento gênico e atividades das ribozimas. Mudanças recentes ocorridas na taxonomia desses patógenos com a criação de famílias, moleculares da interação viróide/hospedeiro. Estão incluídas também algumas características dos virusóides e sua relação evolutiva com os viróides.Palavras-chave adicionais: Interação patógeno/hospedeiro, silenciamento gênico, evolução, ribozima, RNA satélite, patogênese, taxonomia, ABSTRACT Viroids and virusoids: relics of the RNA worldBy the middle of the last century, viruses were considered as the simplest biological entities. The discovery of satellite RNAs and viroids by 1970 was surprising because it revealed the existence of a novel class of self-replicating molecules even simpler, named subviral agents. There are evidences that viroids and virusoids (a class of satellite RNAs) were part of the so-called "RNA world" (that preceded our present world based on DNA and proteins) and for this reason they can be considered as molecular fossils of this ancient period. The simplicity of these subviral agents and the fact that the RNA molecule must interact directly with host factors for completing their infective cycle make these pathogens a model for the study of cellular processes. In the last years, a large number of publications have widened our knowledge of the viroid-host interactions, including pathogenesis mechanisms, movement through the host, gene silencing and ribozyme activity. Recent changes have been introduced in the taxonomy of these pathogens, with the creation of families, genera and species, and new viroids have also been found. The purpose of this review is to present the reader with these recent advances in viroid research, mainly on taxonomy, phylogeny and in molecular aspects of the viroid-host interaction. Some characteristics of virusoids and their evolutionary relationship with viroids are also included.

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Differential Subnuclear Localization of RNA Strands of Opposite Polarity Derived from an Autonomously Replicating Viroid[W]

Cited by 92 publications

References 66 publications

Arabidopsis thaliana has the enzymatic machinery for replicating representative viroid species of the family Pospiviroidae

Arabidopsis thaliana has the enzymatic machinery for replicating representative viroid species of the family Pospiviroidae

A Structured Viroid RNA Serves as a Substrate for Dicer-Like Cleavage To Produce Biologically Active Small RNAs but Is Resistant to RNA-Induced Silencing Complex-Mediated Degradation

Viróides e virusóides: relíquias do mundo de RNA

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