Introns of plant pri‐miRNAs enhance miRNA biogenesis

Dawid Bielewicz,Andrea Barta,Maria Kalyna,Malgorzata Kalak,David Windels,Zofia Szweykowska‐Kulinska,Franck Vazquez,Artur Jarmolowski

doi:10.1038/embor.2013.62

Abstract

Plant MIR genes are independent transcription units that encode long primary miRNA precursors, which usually contain introns. For two miRNA genes, MIR163 and MIR161, we show that introns are crucial for the accumulation of proper levels of mature miRNA. Removal of the intron in both cases led to a drop-off in the level of mature miRNAs. We demonstrate that the stimulating effects of the intron mostly reside in the 5'ss rather than on a genuine splicing event. Our findings are biologically significant as the presence of functional splice sites in the MIR163 gene appears mandatory for pathogen-triggered accumulation of miR163 and proper regulation of at least one of its targets.

Highlights

MicroRNAs are 20–22-nt-long small RNAs that regulate the expression of genes involved in critical developmental programmes or in response to specific environmental conditions [1,2,3,4,5]
To evaluate the significance of introns in pri-miRNAs and whether they influence the level of mature miRNAs, we introduced original or mutated MIR163 constructs controlled by the native MIR163 promoter in the mir163-2 mutant (Fig 1A)
Our experiments have shown that the intron of MIR163 is required for proper biogenesis and function of its mature miRNA

Summary

Introduction

MicroRNAs (miRNAs) are 20–22-nt-long small RNAs that regulate the expression of genes involved in critical developmental programmes or in response to specific environmental conditions [1,2,3,4,5]. A set of 15–20 miRNA families that are evolutionarily highly conserved and serve in the regulation of crucial developmental programmes have been identified. The other miRNA families are lineage- or species-specific, and serve in the regulation of specialized aspects of plant life [6]. Processing of the pri-miRNAs occurs in two steps by the RNAse III enzyme DICER-LIKE1 (DCL1) and its main double-strand RNA-binding partner DRB1/HYL1 [10,11,12]. The biogenesis and function of miRNAs are tightly regulated at several levels to ensure that proper regulation of the mRNA targets is maintained and adjusted in changing environmental conditions that includes posttranscriptional feedback regulation of DCL1 and AGO1 mRNA levels [16]

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Results

Conclusion