Evolution of Plant MicroRNAs
Published Online: 16 APR 2012
Copyright © 2001 John Wiley & Sons, Ltd. All rights reserved.
How to Cite
Tamas, D. 2012. Evolution of Plant MicroRNAs. eLS. .
- Published Online: 16 APR 2012
Microribonucleic acids (miRNAs) are small noncoding regulatory molecules encoded in the genome and generated through several processing steps. They recognise specific messenger RNAs and regulate their expression by cleavage or by translational inhibition. MiRNAs were only discovered approximately 10 years ago but it quickly became evident that they play an important role in development and stress responses. Initially it was thought that all miRNAs are conserved in plants because the technology only allowed to sequence the most abundant miRNAs. However, the development of next generation sequencing technologies allowed researchers to generate millions of sequencing reads in a sample, which resulted in the identification of the less abundant miRNAs. Analysis of large-scale sequencing data revealed that the number of nonconserved miRNAs is much larger than previously thought. This review focuses on the evolution of plant MIRNA genes from protein-coding genes by describing the difference between conserved and nonconserved MIRNA families.
MicroRNAs are small noncoding regulatory molecules.
Primary miRNA transcripts are folded into a stem–loop secondary structure, which is cleaved twice by DICER-LIKE1 releasing the microRNA duplex.
One strand of the microRNA duplex is incorporated into an ARGONAUTE complex and guides the complex to specific mRNAs.
The ARGONAUTE complex usually cleaves the target mRNA but it also suppresses the translation of noncleaved mRNAs.
Some MIRNA genes are ancient and conserved in all embryophytes but there are nonconserved MIRNA families that are only in angiosperms or specific to monocots or dicots. A large number of MIRNA families are even divergent between dicot families.
New MIRNA genes can potentially evolve from any inverted repeats but the most evidence exists for generation from inverse duplication of protein-coding genes followed by deletions and mutations.
Indirect evidence suggests rapid birth and death of MIRNA genes: approximately 1–3 MIRNA genes per million years in the Arabidopsis lineage.
Nonconserved MIRNA genes are weakly expressed, imprecisely processed, show uniform nucleotide divergence and many lack targets, suggesting that they are evolving neutrally.
Nonconserved MIRNA genes could be a source of ‘regulatory diversity’, which can be selected for if they acquire target genes and that is advantageous for the plant, maybe in a new environment.
- small noncoding RNA;
- gene expression regulation;