Department of Plant and Soil Sciences and KTRDC, University of Kentucky, Lexington, KY 40546, USA.
Semin Cell Dev Biol. 2010 Oct;21(8):782-9. doi: 10.1016/j.semcdb.2010.07.009. Epub 2010 Aug 4.
MicroRNAs (miRNAs) are 21-23 nucleotide (nt) non-coding RNAs that play a key role in regulating the expression of protein-coding genes at post-transcriptional levels in plants and animals. MiRNA genes, which serve as genetic buffers and regulators, are primarily located in the intergenic regions of the plant genome. The similar structure of a miRNA promoter to that of a protein-coding gene signifies the likely origin of miRNA genes from the latter. Imperfect "inverted repeats", the hallmark of miRNA genes that defines the asymmetry of the "stem-loop" region of the miRNA precursors (pre-miRNAs), reflect the evolution of miRNA genes from the inverted duplication of their target genes over a long period of time. The deep conservation of most miRNAs and the presence of some of the non-conserved, species-specific miRNAs among various plant species demonstrate a continuous, but frequently an uneven evolutionary process of miRNA genes. Thus, duplication, inversion, mutation, amplification, and other types of genetic drift from protein-coding genes might be the primary events in the genesis and evolution of the miRNA genes. Subsequent co-evolution of the miRNA genes and their target genes ensures the maintenance and the fine-tuning nature of a dynamic gene regulatory network governed by miRNAs in plants.
微小 RNA（miRNA）是 21-23 个核苷酸（nt）的非编码 RNA，在动植物中，它们在后转录水平上对蛋白质编码基因的表达起着关键的调控作用。miRNA 基因作为遗传缓冲和调节物，主要位于植物基因组的基因间区。miRNA 启动子的结构类似于蛋白质编码基因，表明 miRNA 基因可能来源于后者。不完全的“反向重复”是 miRNA 基因的特征，定义了 miRNA 前体（pre-miRNA）“茎环”区域的不对称性，反映了 miRNA 基因是在其靶基因的反向重复过程中，经过长时间的进化而产生的。大多数 miRNA 的高度保守性，以及在不同植物物种中存在一些非保守的、物种特异性的 miRNA，表明 miRNA 基因的进化是一个连续的，但常常是不均匀的过程。因此，从蛋白质编码基因的复制、反转录、突变、扩增和其他类型的遗传漂变可能是 miRNA 基因起源和进化的主要事件。随后 miRNA 基因与其靶基因的共同进化确保了 miRNA 调控的动态基因调控网络在植物中的维持和精细调节特性。
