Transcriptome-Wide Analysis of Uncapped mRNAs in Arabidopsis Reveals Regulation of mRNA Degradation

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Abstract
The composition of the transcriptome is determined by a balance between mRNA synthesis and degradation. An important route for mRNA degradation produces uncapped mRNAs, and this decay process can be initiated by decapping enzymes, endonucleases, and small RNAs. Although uncapped mRNAs are an important intermediate for mRNA decay, their identity and abundance have never been studied on a large scale until recently. Here, we present an experimental method for transcriptome-wide profiling of uncapped mRNAs that can be used in any eukaryotic system. We applied the method to study the prevalence of uncapped transcripts during the early stages of Arabidopsis thaliana flower development. Uncapped transcripts were identified for the majority of expressed genes, although at different levels. By comparing uncapped RNA levels with steady state overall transcript levels, our study provides evidence for widespread mRNA degradation control in numerous biological processes involving genes of varied molecular functions, implying that uncapped mRNA levels are dynamically regulated. Sequence analyses identified structural features of transcripts and cis-elements that were associated with different levels of uncapping. These transcriptome-wide profiles of uncapped mRNAs will aid in illuminating new regulatory mechanisms of eukaryotic transcriptional networks.