Special Issue "Viroid-2018: International Conference on Viroids and Viroid-Like RNAs"
A special issue of Viruses (ISSN 1999-4915).
Deadline for manuscript submissions: 31 March 2019
Viroids are a very intriguing type of infectious agent of higher plants, since they are exclusively constituted by a relatively small molecule (246–401 nt) of circular RNA. Particularly, all evidence indicates that viroid RNAs do not code for proteins. However, despite this simplicity, when viroid RNAs enter appropriate host cells they manage to replicate, move through the plant, and avoid the host defensive response, causing, in many instances, diseases that are most relevant to important agricultural crops. From their discovery in the late 1960s and early 1970s, a great deal is known about viroid biology and biochemistry, and the pathology of viroid diseases. However, more needs to be discovered about aspects, such as viroid replication, traffic and interaction with the host plant; structure of viroid molecules and functional domains; viroid transmission, pathogenesis and disease control; viroid diagnosis and identification of new viroid species. All these topics and more are to be discussed at Viroid-2018, an international conference on viroids and viroid-like RNAs that will be held in Valencia (Spain) 5–7 July, 2018. I invite all researchers in the viroid community, and particularly the participants of Viroid-2018, to present their recent discoveries about all aspects of viroid and viroid-like RNA biology in this Special Issue.
Dr. José-Antonio Daròs
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- viroid-like RNA
- viroid replication
- viroid movement
- viroid structure
- viroid transmission
- viroid pathogenesis
- anti-viroid strategies
- viroid diagnosis
- new viroid species
The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.
Authors: Theodor O. Diener
Abstract: Viroids, the smallest known infectious pathogens, have been isolated only from infected higher plants. Why not from animals? Do they not exist in animals, or do we need methodolo- gies different from those used with plant viroids? Judging from literature, few efforts have been made to find animal viroids, which is surprising, because the first virus discovered was also a plant virus, tobacco mosaic virus, which was only later followed by the discovery of the first animal viruses and eventually to the thousands of viruses now comprising the virus kingdom. Thus, in analogy with the history of virus discovery, one would expect animal viroids not only to exist, but possibly to far outstrip the number and importance of plant viroids.
A search for cited publications touching on the above question yielded few hits and no convincing evidence of the existence of animal viroids, but also not sufficient negative data to conclude that animal viroids do not exist .
What might possibly explain the apparent disinterest of animal- (human-) virologists in the viroid discovery and its possibly important consequences beyond plant pathology? Offhand, we may point out three reasons:
1. an imagined complexity of the plant virologists’ methodologies used for the isolation and characterization of plant viroids, best expressed by Ding , who thought “the classical approaches technically demanding and time consuming,” and thus discouraging in comparison to modern technologies with their plug-in platforms and ready-made intermediates;
2. an excessive anthropocentric bias of many animal and medical investigators, who a priori discount results obtained in plant systems in the mistaken belief that they were of little concern to them, despite the fact that many important biological concepts were first developed in plant, not animal systems, such as, for example, those of mutation, the fundamental laws of genetics, the existence of submicroscopic (viruses) and subviral (viroids) organisms;
3. an understandable hesitation, particularly by young, budding scientists, to enter a field of inquiry that may---or may not---yield pathbreaking new scientific insights, in preference to choosing less dramatic research, which likely leads to publishable results and good positions. They thereby reduce the number of scientists available to attack the more fundamental scientific questions and run the risk of becoming well trained technologists, but not scientists.
Here, I discuss the meager crop of publications I located with some possible significance regarding the existence of animal viroids.
1, Diener, T. O. J. Virol. Antivir. Res, 2016; 5: 4
2. Zhang, Z. et al.PLoS Pathog. 10: e1004553
Title: Next-Generation Sequencing and CRISPR-Cas Proteins in Viroid Research and Diagnostics
Authors: Ahmed Hadidi
Abstract: Advances in next-generation sequencing (NGS) capabilities and the discovery during the last few years that bacteria and archaea have heritable adaptive immunity mediated through clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated Cas proteins, have led to transformative advances in molecular biology, notably DNA and RNA sequencing, gene editing and molecular diagnostics. NGS combined with informatics has been applied to viroids for almost a decade. NGS provides highly efficient, rapid, low cost high-throughput sequencing of viroid genomes and of the 21-24 nt viroid-derived small RNAs (vd-sRNAs) generated during the infection process. These vd-sRNAs, cover frequently the whole viroid genome. NGS has been used in a number of viroid studies including, but not limited to, discovery of novel viroids or viroid variants, detection and identification of known viroids, extending the known viroid host range, viroid-host interactions, viroid evolution and pathogenesis, mutation and quasispecies composition, mRNA targeting, symptom expression, and others. The potential applications of the CRISPR-Cas proteins for targeting viroid-specific nucleotide sites for genome editing were recently reported. Functionally relevant motifs of potato spindle tuber viroid, peach latent mosaic viroid and avocado sunblotch viroid that could be specifically targeted by CRISPR-based technologies were highlighted. The CRISPR-Cas systems have been utilized very recently for detection of two ssRNA human viruses, one synthetic ssRNA and one synthetic dsDNA in a single reaction by visual read out in less than 1.5 h. Multitarget RNA tests by the CRISPR-Cas systems have a good potential for its application as a rapid and accurate diagnostic assay for viroids.
Keywords: clustered regularly interspaced short palindromic repeats (CRISPR); CRISPR-Cas proteins; gene editing; molecular diagnostics; next-generation sequencing (NGS); viroids