Trafficking of the Potato spindle tuber viroid between tomato and Orobanche ramosa

Viroids are the smallest known pathogenic agents. They are noncoding, single-stranded, closed-circular, "naked" RNAs, which replicate through RNA-RNA transcription. Viroids of the Avsunviroidae family possess a hammerhead ribozyme in their sequence, allowing self-cleavage during their replication. To date, viroids have only been detected in plant cells. Here, we investigate the replication of Avocado sunblotch viroid (ASBVd) of the Avsunviroidae family in a nonconventional host, the yeast Saccharomyces cerevisiae. We demonstrate that ASBVd RNA strands of both polarities are able to self-cleave and to replicate in a unicellular eukaryote cell. We show that the viroid monomeric RNA is destabilized by the nuclear 3 and the cytoplasmic 5 RNA degradation pathways. For the first time, our results provide evidence that viroids can replicate in other organisms than plants and that yeast contains all of the essential cellular elements for the replication of ASBVd.Viroids are the smallest and the simplest eukaryotic known pathogens (12). They are single-stranded circular RNAs capable of infecting plants and range from 246 to 401 nucleotides (nt). However, some variants of 120 or 475 nt are referenced in the subviral RNA database (47). Unlike viruses, they do not code for any protein, they are devoid of capsid or envelope, and are highly structured (13, 58). More than 34 viroid species have been described; they are divided into two families: the Pospiviroidae and the Avsunviroidae. Viroids of the Pospiviroidae family replicate via an RNA rolling-circle mechanism in the nucleus, and in the chloroplasts for the members of the Avsunviroidae family. Viroids move through the plant via the phloem and plasmodesmata that are part of the plant's vascular system and are transmitted by mechanical means, vegetative reproduction, and via seeds and insects (14,15,42). Members of the Avsunviroidae family such as Avocado sunblotch viroid (ASBVd) contain a catalytic hammerhead ribozyme and replicate through the following mechanism (20,21,53). The infectious monomeric circular RNA, which has positive-strand [(ϩ)] polarity, is transcribed by a host RNA polymerase, yielding oligomeric negative strands that self-cleave via the viroid ribozyme into monomers and circularize into negative-strand [(Ϫ)] circular viroids. These RNA species serve as templates to form (ϩ) polarity RNAs following the same steps in a symmetrical manner. According to this replication mechanism, the ribozyme undergoes self-cleavage on RNAs of both polarities. Therefore, both (ϩ) and (Ϫ) monomeric circular RNAs accumulate in tissues infected by Avsunviroidae.Based on these characteristics, ancestral viroids might have been present in an ancient RNA world (11, 23), one of the major scenarios of evolution in which the functional properties of nucleic acids and proteins observed today would have originally been performed by ancestral RNA molecules (2,30,37,41). In this context, it is interesting to explore the behavior of viroids and of other phylogenetically related satellit...

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“…The mutation frequency is probably low, as was observed for PSTVd variants isolated from Orobanche ramosa (59).…”

Section: Discussionmentioning

confidence: 69%

Replication ofAvocado Sunblotch Viroidin the YeastSaccharomyces cerevisiae

Delan-Forino

Maurel

Torchet

2011

J Virol

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“…Viroid host range expansion represents one of the best examples of the fastest natural evolution of RNA sequences/structures, involving no protein coding, to attain new biological functions. Recent work showed unidirectional trafficking of PSTVd from tomato to parasitic plant Orobanche ramosa and identified of O. ramosa ‐originated PSTVd variants that replicate with different efficiencies in tomato 122. This introduced a promising new experimental system to study the mechanisms of RNA trafficking and replication as well as viroid host range determination.…”

Section: Resultsmentioning

confidence: 99%

Viroids: self‐replicating, mobile, and fast‐evolving noncoding regulatory RNAs

Ding

2010

WIREs RNA

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Viroids are small, circular, and noncoding RNAs that infect plants. They replicate in the nucleus or chloroplast and then traffic from cell to cell and from organ to organ to establish systemic infection. Viroids achieve nearly all of the biological functions by directly interacting with host cellular factors. Viroid replication, together with replication of human hepatitis delta virus, demonstrates the biological novelty and significance of RNA-dependent RNA polymerase activities of DNA-dependent RNA polymerases. Viroid systemic infection uncovers a new biological principle--the role of three-dimensional RNA structural motifs mediating RNA trafficking between specific cells. Viroid diseases are virtually the consequences of host gene regulation by noncoding RNAs. A viroid RNA has the highest in vivo mutation rate among all known nucleic acid replicons. The host range of many viroids is expanding, essentially as a result of continuing and fast evolution of noncoding sequences/structures to gain new biological functions. Here, I discuss recent progress in these areas, emphasizing the broad significance of viroid research to the discovery of fundamental biological principles.

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“…However, there is evidence that phloem-mobile virus particles move between host and parasite in the holoparasite Phelipanche (syn. Orobanche ) ramosa [14] and phloem continuity has been observed in Orobanche crenata [15] . The mechanisms of transport between host phloem and parasite phloem likely vary in different parasites from direct phloem connections [15] to transport via apoplastic pathways.…”

Section: Introductionmentioning

confidence: 99%

Functional genomics of a generalist parasitic plant: Laser microdissection of host-parasite interface reveals host-specific patterns of parasite gene expression

et al. 2013

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BackgroundOrobanchaceae is the only plant family with members representing the full range of parasitic lifestyles plus a free-living lineage sister to all parasitic lineages, Lindenbergia. A generalist member of this family, and an important parasitic plant model, Triphysaria versicolor regularly feeds upon a wide range of host plants. Here, we compare de novo assembled transcriptomes generated from laser micro-dissected tissues at the host-parasite interface to uncover details of the largely uncharacterized interaction between parasitic plants and their hosts.ResultsThe interaction of Triphysaria with the distantly related hosts Zea mays and Medicago truncatula reveals dramatic host-specific gene expression patterns. Relative to above ground tissues, gene families are disproportionally represented at the interface including enrichment for transcription factors and genes of unknown function. Quantitative Real-Time PCR of a T. versicolor β-expansin shows strong differential (120x) upregulation in response to the monocot host Z. mays; a result that is concordant with our read count estimates. Pathogenesis-related proteins, other cell wall modifying enzymes, and orthologs of genes with unknown function (annotated as such in sequenced plant genomes) are among the parasite genes highly expressed by T. versicolor at the parasite-host interface.ConclusionsLaser capture microdissection makes it possible to sample the small region of cells at the epicenter of parasite host interactions. The results of our analysis suggest that T. versicolor’s generalist strategy involves a reliance on overlapping but distinct gene sets, depending upon the host plant it is parasitizing. The massive upregulation of a T. versicolor β-expansin is suggestive of a mechanism for parasite success on grass hosts. In this preliminary study of the interface transcriptomes, we have shown that T. versicolor, and the Orobanchaceae in general, provide excellent opportunities for the characterization of plant genes with unknown functions.

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Trafficking of the Potato spindle tuber viroid between tomato and Orobanche ramosa

Cited by 15 publications

References 45 publications

Replication ofAvocado Sunblotch Viroidin the YeastSaccharomyces cerevisiae

Replication ofAvocado Sunblotch Viroidin the YeastSaccharomyces cerevisiae

Viroids: self‐replicating, mobile, and fast‐evolving noncoding regulatory RNAs

Functional genomics of a generalist parasitic plant: Laser microdissection of host-parasite interface reveals host-specific patterns of parasite gene expression

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