Viroids and Viroid Diseases of Plants

Flores, Ricardo; Serio, Francesco Di; Navarro, Beatriz; Durán-Vila, N.; Owens, Robert A.

doi:10.1002/9781118025666.ch12

Cited by 18 publications

(19 citation statements)

References 197 publications

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“…The evidence supporting this notion is compelling and includes detection and characterization in plants infected by members of both families of viroid-derived small RNAs (vd-sRNAs) with the typical properties of the small interfering (si) and micro (mi) RNAs, which by loading the RNA-induced silencing complex (RISC), guide it against specific targets (see for a review Flores et al, 2011a). Some of the vd-sRNAs may be relevant for pathogenesis.…”

Section: Concluding Reflections and Prospectsmentioning

confidence: 99%

Viroids: From Genotype to Phenotype Just Relying on RNA Sequence and Structural Motifs

Flores¹,

Serra²,

Minoia³

et al. 2012

Front. Microbio.

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As a consequence of two unique physical properties, small size and circularity, viroid RNAs do not code for proteins and thus depend on RNA sequence/structural motifs for interacting with host proteins that mediate their invasion, replication, spread, and circumvention of defensive barriers. Viroid genomes fold up on themselves adopting collapsed secondary structures wherein stretches of nucleotides stabilized by Watson–Crick pairs are flanked by apparently unstructured loops. However, compelling data show that they are instead stabilized by alternative non-canonical pairs and that specific loops in the rod-like secondary structure, characteristic of Potato spindle tuber viroid and most other members of the family Pospiviroidae, are critical for replication and systemic trafficking. In contrast, rather than folding into a rod-like secondary structure, most members of the family Avsunviroidae adopt multibranched conformations occasionally stabilized by kissing-loop interactions critical for viroid viability in vivo. Besides these most stable secondary structures, viroid RNAs alternatively adopt during replication transient metastable conformations containing elements of local higher-order structure, prominent among which are the hammerhead ribozymes catalyzing a key replicative step in the family Avsunviroidae, and certain conserved hairpins that also mediate replication steps in the family Pospiviroidae. Therefore, different RNA structures – either global or local – determine different functions, thus highlighting the need for in-depth structural studies on viroid RNAs.

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Section: Concluding Reflections and Prospectsmentioning

confidence: 99%

Viroids: From Genotype to Phenotype Just Relying on RNA Sequence and Structural Motifs

Flores¹,

Serra²,

Minoia³

et al. 2012

Front. Microbio.

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“…The approximately 30 viroid species reported so far have been assigned to the taxonomic families Pospiviroidae , grouping the type species Potato spindle tuber viroid (PSTVd) and many others that replicate and accumulate in the nucleus, and Avsunviroidae , clustering the type species Avocado sunblotch viroid (ASBVd) and three other viroids replicating and accumulating in plastids (mainly chloroplasts; Owens et al, 2011). Members of both families induce severe diseases in certain hosts, although in some viroid-host combinations the infection remains latent (Flores et al, 2011). Viroid diseases are characterized by macroscopic symptoms that may include stunting, alterations affecting leaves (epinasty, vein clearing, distortion, discoloration, mottling, and necrosis) and bark (cankers, scaling, cracking), and malformations of tubers, flowers, and fruits (in the last two organs frequently accompanied with color breaking).…”

Section: Introductionmentioning

confidence: 99%

Cytopathic Effects Incited by Viroid RNAs and Putative Underlying Mechanisms

Serio¹,

Stradis²,

Delgado³

et al. 2013

Front. Plant Sci.

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Viroids are infectious agents identified only in plants so far. In contrast to viruses, the genome of viroids is composed of a tiny circular RNA (250–400 nt) not coding for proteins, but containing in its compact structure all the information needed for parasitizing the transcriptional and RNA trafficking machineries of their hosts. Viroid infections are frequently accompanied by cellular and developmental disorders that ultimately result in macroscopic symptoms. The molecular events linking the structural domains of viroid RNAs with cellular and macroscopic alterations remain largely unexplored, although significant progress has been lately achieved in one specific viroid-host combination, highlighting the ability of viroids to strongly interfere with their host RNA regulatory networks. Cytopathic effects induced by nuclear-replicating viroids, which were investigated since early studies on viroids, consist in irregular proliferations of cell membranes (paramural bodies or plasmalemmasomes), cell wall distortions, and chloroplast malformations. Different alternatives have been proposed regarding how these cytological alterations may influence the onset of macroscopic symptoms. Recently, the cytopathology and histopathology incited by a chloroplast-replicating viroid have been investigated in depth, with defects in chloroplast development having been related to specific molecular events that involve RNA silencing and impairment of chloroplast ribosomal RNA maturation. On this basis, a tentative model connecting specific cytopathologic alterations with symptoms has been put forward. Here, early and more recent studies addressing this issue will be reviewed and reassessed in the light of recent advances in the regulatory roles of small RNAs.

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“…Viroids are naked, circular, long non-coding RNA pathogens that range in size from 246 to 467 nt, causing plant diseases of economic importance [14]. They were reported for the first time in 1971 in the spindle tuber disease of potato [8].…”

Section: -General Aspectsmentioning

confidence: 99%

“…Dahlia latent viroid) and await approval by the International committee on taxonomy of viruses (ICTV) [17]. Since their first discovery, viroid infections have been reported in every continent with different economic impact depending on their host and the local phytosanitary measures [14,18]. In the 2014 quarantine pest list of the European and Mediterranean plant protection organization (EPPO) there are three viroids of the Pospiviroidae family present: Coconut cadangecadang viroid, Chrysanthemun stunt viroid and Potato tuber spindle viroid (PSTVd) and one, Tomato apical stunt viroid, in the alert list [19].…”

Section: -General Aspectsmentioning

confidence: 99%