Agius Claire, Eamens Andrew L, Millar Anthony A, Watson John M, Wang Ming-Bo
Division of Plant Industry, CSIRO, Canberra, ACT, Australia.
Methods Mol Biol. 2012;894:17-38. doi: 10.1007/978-1-61779-882-5_2.
Given the widespread impact of RNA silencing on the Arabidopsis thaliana genome, it is indeed remarkable that this means of gene regulation went undiscovered for so long. Since the publication of landmark papers in 1998 (Fire et al., Nature 391:806-811, 1998; Waterhouse et al., Proc Natl Acad Sci U S A 95:13959-13964, 1998), intense research efforts have resulted in much progress from the speculation of Mello and colleagues that "the mechanisms underlying RNA interference probably exist for a biological purpose" (Fire et al., Nature 391:806-811, 1998). Across the eukaryotic kingdom, with the notable exception of Saccharomyces cerevisiae (Moazed, Science 326:544-550, 2009), the importance of small RNA-driven gene regulation has been recognized and implicated in central developmental processes as well as in aberrant and diseased states. Plants have by far the most complex RNA-based control of gene expression (Wang et al., Floriculture, ornamental and plant biotechnology, vol. III, 2006). Four distinct RNA silencing pathways have been recognized in plants, albeit with considerable conservation of the molecular components. These pathways are directed by various small RNA species, including microRNAs (miRNAs), trans-acting small interfering RNAs (siRNA) (ta-siRNAs), repeat-associated siRNAs (ra-siRNAs), and natural antisense transcript siRNAs (nat-siRNAs). The effective functionality of each of these pathways appear to be fundamental to the integrity of A. thaliana. Furthermore, in response to viral invasion, plants synthesize viral sRNAs as a means of defense. This process may in fact reflect the ancient origins of RNA silencing: plants may have evolved RNA silencing pathways as a defense mechanism against foreign nucleic acid species in the absence of an immune system (Wang and Metzlaff, Curr Opin Plant Biol 8:216-222, 2005). The generation of viral siRNAs is a particularly interesting illustration of RNA silencing as it provides a context to explore the potential to harness a naturally occurring system to the end goal of artificially engineering viral resistance.
鉴于RNA沉默对拟南芥基因组具有广泛影响，这种基因调控方式长期未被发现着实令人惊讶。自1998年标志性论文发表以来（Fire等人，《自然》391:806 - 811，1998；Waterhouse等人，《美国国家科学院院刊》95:13959 - 13964，1998），经过深入研究，梅洛及其同事推测“RNA干扰背后的机制可能具有生物学意义”（Fire等人，《自然》391:806 - 811，1998），现已取得了很大进展。在整个真核生物界，除了酿酒酵母（Moazed，《科学》326:544 - 550，2009）这一显著例外，小RNA驱动的基因调控的重要性已得到认可，并与核心发育过程以及异常和疾病状态相关。到目前为止，植物拥有基于RNA的最复杂的基因表达调控机制（Wang等人，《花卉栽培、观赏植物与植物生物技术》，第三卷，2006）。在植物中已识别出四种不同的RNA沉默途径，尽管分子成分有相当程度的保守性。这些途径由各种小RNA种类引导，包括微小RNA（miRNA）、反式作用小干扰RNA（siRNA）（ta - siRNA）、重复相关siRNA（ra - siRNA）和天然反义转录本siRNA（nat - siRNA）。这些途径中每一种的有效功能似乎对于拟南芥的完整性至关重要。此外，为应对病毒入侵，植物合成病毒sRNA作为一种防御手段。这一过程实际上可能反映了RNA沉默的古老起源：在缺乏免疫系统的情况下，植物可能进化出RNA沉默途径作为抵御外来核酸种类的防御机制（Wang和Metzlaff，《植物生物学当前观点》8:216 - 222，2005）。病毒siRNA的产生是RNA沉默的一个特别有趣的例证，因为它为探索利用自然发生的系统实现人工工程抗病毒这一最终目标的潜力提供了背景。
