Evolution of plant microRNA gene families

MicroRNAs(miRNAs)are important post-transcriptional regulators of their target genes in plants and animals,miR-NAs are usually 20-24 nucleotides long.Despite their unusually small sizes,the evolutionary history of miRNA genefamilies seems to be similar to their protein-coding counterparts.In contrast to the small but abundant miRNA familiesin the animal genomes,plants have fewer but larger miRNA gene families.Members of plant miRNA gene familiesare often highly similar,suggesting recent expansion via tandem gene duplication and segmental duplication events.Although many miRNA genes are conserved across plant species,the same gene family varies significantly in size andgenomic organization in different species,which may cause dosage effects and spatial and temporal differences in targetgene regulations.In this review,we summarize the current progress in understanding the evolution of plant miRNA genefamilies.