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Deep-sequencing of the peach latent mosaic viroid reveals new aspects of population heterogeneity.

ABSTRACT: Viroids are small circular single-stranded infectious RNAs characterized by a relatively high mutation level. Knowledge of their sequence heterogeneity remains largely elusive and previous studies, using Sanger sequencing, were based on a limited number of sequences. In an attempt to address sequence heterogeneity from a population dynamics perspective, a GF305-indicator peach tree was infected with a single variant of the Avsunviroidae family member Peach latent mosaic viroid (PLMVd). Six months post-inoculation, full-length circular conformers of PLMVd were isolated and deep-sequenced. We devised an original approach to the bioinformatics refinement of our sequence libraries involving important phenotypic data, based on the systematic analysis of hammerhead self-cleavage activity. Two distinct libraries yielded a total of 3,939 different PLMVd variants. Sequence variants exhibiting up to ?17% of mutations relative to the inoculated viroid were retrieved, clearly illustrating the high level of divergence dynamics within a unique population. While we initially assumed that most positions of the viroid sequence would mutate, we were surprised to discover that ?50% of positions remained perfectly conserved, including several small stretches as well as a small motif reminiscent of a GNRA tetraloop which are the result of various selective pressures. Using a hierarchical clustering algorithm, the different variants harvested were subdivided into 7 clusters. We found that most sequences contained an average of 4.6 to 6.4 mutations compared to the variant used to initially inoculate the plant. Interestingly, it was possible to reconstitute and compare the sequence evolution of each of these clusters. In doing so, we identified several key mutations. This study provides a reliable pipeline for the treatment of viroid deep-sequencing. It also sheds new light on the extent of sequence variation that a viroid population can sustain, and which may give rise to a quasispecies.

SUBMITTER: Glouzon JP

PROVIDER: S-EPMC3907566 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Deep-sequencing of the peach latent mosaic viroid reveals new aspects of population heterogeneity.

Glouzon Jean-Pierre Sehi JP Bolduc François F Wang Shengrui S Najmanovich Rafael J RJ Perreault Jean-Pierre JP

PloS one 20140130 1

Viroids are small circular single-stranded infectious RNAs characterized by a relatively high mutation level. Knowledge of their sequence heterogeneity remains largely elusive and previous studies, using Sanger sequencing, were based on a limited number of sequences. In an attempt to address sequence heterogeneity from a population dynamics perspective, a GF305-indicator peach tree was infected with a single variant of the Avsunviroidae family member Peach latent mosaic viroid (PLMVd). Six month ...[more]

PMID: 24498066

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Project description:BackgroundIt has been observed that following viroid infection, there is an accumulation of viroid-derived siRNAs in infected plants. Some experimental results suggest that these small RNAs may be produced by the plant defense system to protect it from infection, indicating that viroids can elicit the RNA-silencing pathways. The objective of this study is to identify in the peach latent mosaic viroid (PLMVd), a model RNA genome, the regions that are most susceptible to RNA interference machinery.ResultsThe RNA isolated from an infected tree have been used to sequence in parallel viroid species and small non-coding RNA species. Specifically, PLMVd RNAs were amplified, cloned and sequenced according to a conventional approach, while small non-coding RNAs were determined by high-throughput sequencing. The first led to the typing of 18 novel PLMVd variants. The second provided a library of small RNAs including 880 000 sequences corresponding to PLMVd-derived siRNAs, which makes up 11.2% of the sequences of the infected library. These siRNAs contain mainly 21-22 nucleotide RNAs and are equivalently distributed between the plus and the minus polarities of the viroid. They cover the complete viroid genome, although the amount varies depending on the regions. These regions do not necessarily correlate with the double-stranded requirement to be a substrate for Dicer-like enzymes. We noted that some sequences encompass the hammerhead self-cleavage site, indicating that the circular conformers could be processed by the RNA-silencing machinery. Finally, a bias in the relative abundance of the nature of the 5' nucleotides was observed (A, U >> G, C).ConclusionsThe approach used provided us a quantitative representation of the PLMVd-derived siRNAs retrieved from infected peach trees. These siRNAs account for a relatively large proportion of the small non-coding RNAs. Surprisingly, the siRNAs from some regions of the PLMVd genome appear over-represented, although these regions are not necessarily forming sufficiently long double-stranded structures to satisfy Dicer-like criteria for substrate specificity. Importantly, this large library of siRNAs gave several hints as to the components of the involved silencing machinery.

Dataset Information

Deep-sequencing of the peach latent mosaic viroid reveals new aspects of population heterogeneity.

Publications

Deep-sequencing of the peach latent mosaic viroid reveals new aspects of population heterogeneity.

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