Abstract
BackgroundIn the past few decades, non-coding RNAs (ncRNAs) have emerged as important regulators of gene expression in eukaryotes. Most studies of ncRNAs in plants have focused on the identification of silencing microRNAs (miRNAs) and small interfering RNAs (siRNAs). Another important family of ncRNAs that has been well characterized in plants is the small nucleolar RNAs (snoRNAs) and the related small Cajal body-specific RNAs (scaRNAs). Both target chemical modifications of ribosomal RNAs (rRNAs) and small nuclear RNAs (snRNAs). In plants, the snoRNA genes are organized in clusters, transcribed by RNA Pol II from a common promoter and subsequently processed into mature molecules. The promoter regions of snoRNA polycistronic genes in plants are highly enriched in two conserved cis-regulatory elements (CREs), Telo-box and Site II, which coordinate the expression of snoRNAs and ribosomal protein coding genes throughout the cell cycle.ResultsIn order to identify novel ncRNA genes, we have used the snoRNA Telo-box/Site II motifs combination as a functional promoter indicator to screen the Arabidopsis genome. The predictions generated by this process were tested by detailed exploration of available RNA-Seq and expression data sets and experimental validation. As a result, we have identified several snoRNAs, scaRNAs and 'orphan' snoRNAs. We also show evidence for 16 novel ncRNAs that lack similarity to any reported RNA family. Finally, we have identified two dicistronic genes encoding precursors that are processed to mature snoRNA and miRNA molecules. We discuss the evolutionary consequences of this result in the context of a tight link between snoRNAs and miRNAs in eukaryotes.ConclusionsWe present an alternative computational approach for non-coding RNA detection. Instead of depending on sequence or structure similarity in the whole genome screenings, we have explored the properties of promoter regions of well-characterized ncRNAs. Interestingly, besides expected ncRNAs predictions we were also able to recover single precursor arrangement for snoRNA-miRNA. Accompanied by analyses performed on rice sequences, we conclude that such arrangement might have interesting functional and evolutionary consequences and discuss this result in the context of a tight link between snoRNAs and miRNAs in eukaryotes.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2221-x) contains supplementary material, which is available to authorized users.
Highlights
In the past few decades, non-coding RNAs have emerged as important regulators of gene expression in eukaryotes
Computational approach to the identification of novel ncRNAs containing Telo-box and Site II regulatory elements To systematically identify novel non-coding RNA genes directed by Telo-box and Site II elements (TeloSII) cis-regulatory elements in Arabidopsis, we assembled a customized pipeline (Fig. 1)
We considered a region as a candidate promoter if both the Telo-box and Site II elements (TeloSII) were found in a sequence window of 1 kb as suggested earlier by Gaspin et al [27]
Summary
In the past few decades, non-coding RNAs (ncRNAs) have emerged as important regulators of gene expression in eukaryotes. Most studies of ncRNAs in plants have focused on the identification of silencing microRNAs (miRNAs) and small interfering RNAs (siRNAs). Another important family of ncRNAs that has been well characterized in plants is the small nucleolar RNAs (snoRNAs) and the related small Cajal body-specific RNAs (scaRNAs). In silico approaches represent another important strategy for the identification of novel ncRNAs in a variety of sequenced genomes Most of these techniques use algorithms that consider structural RNA features that are conserved in known RNA families. We propose a distinct approach that employs conserved promoter elements of plant snoRNA genes for the identification of novel ncRNAs in the Arabidopsis genome
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