Ito Hidetaka
Faculty of Science, Hokkaido University, Kita-ku, Sapporo, Japan.
Genes Genet Syst. 2013;88(1):3-7. doi: 10.1266/ggs.88.3.
RNA interference is now a well-recognized post-transcriptional mechanism for regulation of gene expression in both animals and plants. In this process, microRNAs (miRNAs) direct silencing complexes to complementary RNA sequences, leading to either degradation or repression of translation. Plants also contain another type of small RNA, small interfering RNAs (siRNAs), that play a role in gene silencing by directing cytosine methylation activities of complementary DNA sequences and thus, differ from miRNAs. This nuclear regulation system is referred to as RNA-directed DNA methylation (RdDM). In plant genomes, transposable elements were initially thought to be regulated by DNA methylation alone. However, several recent reports have revealed that siRNAs and RdDM also play crucial roles in silencing of transposons and endogenous repeats. It is also becoming apparent that transposons are subjected to different levels of regulation in response to developmental and environmental cues. Transposons are tightly regulated in germ cells to protect the host genome from transgenerational mutagenic activity. In plants, transposons are also activated by biotic and abiotic stress. The regulation of transposons in these different situations has been associated with both the DNA methylation and siRNA-mediated regulation systems, suggesting that plants likely evolved "multi-lock" systems for transposon regulation to ensure tight control during the developmental phase and environmental changes.
RNA干扰现在是一种在动物和植物中都得到充分认可的转录后基因表达调控机制。在这个过程中，微小RNA（miRNA）引导沉默复合体作用于互补RNA序列，导致翻译的降解或抑制。植物还含有另一种类型的小RNA，即小干扰RNA（siRNA），它通过引导互补DNA序列的胞嘧啶甲基化活动在基因沉默中发挥作用，因此与miRNA不同。这种核调控系统被称为RNA指导的DNA甲基化（RdDM）。在植物基因组中，转座子最初被认为仅受DNA甲基化调控。然而，最近的几份报告表明，siRNA和RdDM在转座子和内源性重复序列的沉默中也起着关键作用。越来越明显的是，转座子会根据发育和环境线索受到不同程度的调控。转座子在生殖细胞中受到严格调控，以保护宿主基因组免受跨代诱变活性的影响。在植物中，转座子也会被生物和非生物胁迫激活。这些不同情况下转座子的调控与DNA甲基化和siRNA介导的调控系统都有关联，这表明植物可能进化出了“多重锁定”的转座子调控系统，以确保在发育阶段和环境变化期间进行严格控制。
