Regulation of gene expression by novel plant-specific small nucleolar RNAs

植物的多样性，植物如何生长发育，以及它们如何应对外界刺激，如病原体/害虫的攻击或逆境条件，都取决于植物物种的基因含量和基因表达的调控。基因在许多不同的水平上受到调控。一个重要的水平是基因的开启或关闭，或上升或下降，称为转录控制。第二个水平发生在基因转录或复制成RNA之后，称为转录后控制。在这个水平上，rna可以以不同的方式加工或靶向破坏或降解。有许多不同的转录后控制机制，其中选择性剪接和小RNA分子靶向是最重要的两种。选择性剪接是指基因转录物的不同部分以不同的组合连接在一起，从而从一个基因中产生多个信使RNA （mRNA）。由此产生的mrna可以被翻译成具有不同功能的蛋白质，或者可以作为降解的目标。小RNA分子如microRNAs （miRNAs）或短干扰RNA （sirna）可以与靶mrna碱基配对并诱导其降解，从而沉默靶基因的表达。这介绍了通过其他通常小的调节rna的碱基配对的特定相互作用来调节mrna的概念。细胞中的许多基本过程依赖于小RNA与其他大RNA物种相互作用的活性。例如，在核糖体中发现的核糖体RNA （rRNA）物种的产生需要小核仁RNA （snoRNAs）将前体rRNA切割成特定的rRNA。信使rna由前体mrna通过剪接过程产生，其中内含子被识别和去除。这一过程依赖于小核rna对内含子信号的识别和剪接反应本身。最近，数百种mirna和sirna通过促进靶mrna的降解或干扰其翻译而被确定为表达调节剂。虽然不同的小rna家族被认为与相当特定的目标rna相互作用并调节，但已经发现了一些例子，在这些例子中，小rna获得了其他小rna的特征，从而使它们的功能范围不像以前认为的那样有限。SnoRNAs通过碱基配对参与rRNA的产生。在动物中，已经发现一些snoRNAs（称为“孤儿”snoRNAs）不与rnas碱基对，但可以与mrna碱基对。一些人类孤儿snoRNAs能够影响mrna的选择性剪接，这显示了snoRNAs新功能的进化。我们已经在植物中发现了孤儿snorna，特别是一组全新的植物特异性snorna。这些snoRNAs与mrna具有互补性，本提案的主要目的是表征这些新的snoRNAs及其作为植物基因调控新模式与mrna功能相互作用的意想不到的潜力。了解基因调控各个方面的复杂性和微妙性对于理解植物如何生长和生存以及预测对变化环境的反应非常重要。这种调节模式本身就是表达控制领域的兴趣所在。此外，由于它依赖于一种稳定的RNA，该RNA可以靶向mrna并与mrna进行碱基配对，因此存在着以一种受调节的方式修饰snoRNA以靶向其他特定基因和过程的潜力。这些信息将成为旨在理解调节基因表达和生物过程的相互作用网络的系统方法的一个组成部分。

Plant diversity, how plants grow and develop, and how they respond to external stimuli such as attack by pathogens/pests or stress conditions, all depend on the gene content of the plant species and the regulation of expression of the genes. Genes are regulated at many different levels. One important level is where genes are turned on or off or up or down - called transcriptional control. A second level occurs after the gene is transcribed or copied into RNA - called post-transcriptional control. At this level RNAs can be processed in different ways or targeted for destruction or degradation. There are many different mechanisms of post-transcriptional control of which alternative splicing and targeting by small RNA molecules are two of the most important. Alternative splicing is where different portions of a gene transcript are joined in different combinations to generate more than one messenger RNA (mRNA) from a gene. The resultant mRNAs can be translated into proteins with different functions or can be targeted for degradation. Small RNA molecules such as microRNAs (miRNAs) or short-interfering RNAs (siRNAs) can base-pair with target mRNAs and induce their degradation thereby silencing expression of the target gene. This introduces the concept of regulation of mRNAs by the specific interaction via base-pairing of other, usually small, regulatory RNAs. Many essential processes in the cell depend on the activity of small RNAs interacting with other, larger RNA species. For example, the production of ribosomal RNA (rRNA) species found in ribosomes requires small nucleolar RNAs (snoRNAs) to cut the precursor rRNA into specific rRNAs. Messenger RNAs are produced from precursor mRNAs by the process of splicing where introns are recognised and removed. This process depends on small nuclear RNAs for recognition of intron signals and the splicing reaction itself. More recently, hundreds of miRNAs and siRNAs have been identified as regulators of expression by promoting degradation of target mRNAs or interfering with their translation. While different families of small RNAs are thought to interact with and regulate fairly specific sets of target RNAs, examples have been found where small RNAs have picked up the characteristics of other small RNAs such that their range of functionality is not as restricted as previously thought. SnoRNAs are involved in production of rRNA via base-pairing. In animals, some snoRNAs (called 'orphan' snoRNAs) have been found which do not base-pair with rRNAs but instead can base-pair with mRNAs. Some of the human orphan snoRNAs are able to affect alternative splicing of mRNAs showing the evolution of novel functions for snoRNAs. We have found orphan snoRNAs in plants and, in particular, a group of entirely novel, plant-specific snoRNAs. These snoRNAs have complementarity to mRNAs and the major thrust of this proposal is to characterise these new snoRNAs and their unexpected potential to functionally interaction with mRNAs as a new mode of gene regulation in plants. Knowledge of the complexity and subtlety of all aspects of gene regulation is important in understanding how plants grow and survive and in the prediction of responses to changing environments. This mode of regulation is of interest per se in the field of expression control. In addition, because it relies on a stable RNA which can target and base-pair with mRNAs, the potential exists to modify the snoRNA to target other specific genes and processes in a regulated manner. Such information will be an integral part of systems approaches aimed at understanding the interaction networks which regulate gene expression and biological processes.