Mechanisms governing floral stem cell maintenance and miRNA functions in Arabidop

发育生物学的一个基本问题是多能干细胞是如何维持的，以及它们如何在多细胞生物中分化成不同的谱系。模式植物拟南芥（Arabidopsis thaliana）的花发育为解决干细胞生物学中的关键问题提供了一个很好的系统。我们的长期目标之一是揭示控制花干细胞维持和终止的机制。我们和其他人已经发现了一个尚不完整的由三种转录因子叠加的基于microRNA （miRNA）的转录后机制的网络，该机制支配着花干细胞的维持。在本研究中，我们将通过鉴定花干细胞调控的核心成分来扩展这一网络。我们将1)鉴定这两个关键转录因子的靶基因，2)将新发现的花干细胞调控因子ARF2、ARF3和ARF4，以及调控这三个转录因子基因的小RNA纳入现有的花干细胞调控框架，3)探索Polycomb蛋白在花干细胞终止中的作用。mirna是影响包括发育在内的许多生物过程的序列特异性调控分子。反式sirna （ta- sirna）是一类具有重要发育作用的植物特异性mirna样小rna。另一个长期研究目标是剖析小rna的生物发生和作用模式的一般机制，并研究特定mirna或ta- sirna的生物发生或活性如何在发育过程中被调节。虽然miRNA生物发生的主要框架已经建立，但miRNA如何抑制靶基因的表达目前仍存在很大争议。在了解特定小rna的活动如何在发育环境中受到调节方面，该领域还处于非常早期的阶段。解剖mirna的作用模式和理解小RNA活性在发育过程中如何被调节的关键是识别介导或调节小RNA活性的蛋白质。我们已经鉴定出两个这样的蛋白，AGO10和AMP1在小rna介导的靶基因调控中。本研究旨在揭示这两种蛋白的分子功能。这项工作无疑将为干细胞调控和miRNA功能提供新的见解。了解干细胞在植物体内是如何维持和终止的，将有助于得出支配干细胞生物学的基本原理，并有助于干细胞在再生医学中的最终应用。由于miRNA在植物和动物之间的生物发生和功能机制高度保守，我们在miRNA功能机制理解方面的进展将直接影响我们利用小rna的力量来对抗病原体和人类疾病的能力。

DESCRIPTION (provided by applicant): A fundamental question in developmental biology is how pluripotent stem cells are maintained and how they differentiate into various lineages in multicellular organisms. Flower development in the model plant Arabidopsis thaliana offers a great system to address key questions in stem cell biology. One of our long-term goals is to uncover the mechanisms that govern the maintenance and termination of floral stem cells. We and others have uncovered an as yet incomplete network of three transcription factors superimposed by a microRNA (miRNA)-based posttranscriptional mechanism that governs the maintenance of floral stem cells. In the proposed research, we will expand this network by identifying core components at the heart of floral stem cell regulation. We will 1) identify target genes of the two key transcription factors, 2) incorporate the newly identified floral stem cell regulators, ARF2, ARF3 and ARF4, and the small RNA that regulates the three transcription factor genes into the existing framework of floral stem cell regulation, and 3) probe the role of the Polycomb group proteins in floral stem cell termination. miRNAs are sequence-specific regulatory molecules that impact numerous biological processes including development. The trans-acting siRNAs (ta-siRNAs) are a class of plant-specific, miRNA-like small RNAs with important developmental roles. Another long-term research goal is to dissect the general mechanisms underlying the biogenesis and mode of action of small RNAs and to study how the biogenesis or activities of specific miRNAs or ta-siRNAs are modulated in development. Whereas the major framework of miRNA biogenesis is established, how miRNAs inhibit target gene expression is highly controversial at present. The field is at its very early stages of understanding how the activities of specific small RNAs are regulated in developmental contexts. A key to dissecting the mode of action of miRNAs and understanding how small RNA activity is regulated in development is to identify proteins that mediate or modulate the activities of small RNAs. We have identified two such proteins, AGO10 and AMP1 in small RNA-mediated target gene regulation. The proposed research is aimed at uncovering the molecular functions of these two proteins. The proposed work will undoubtedly provide novel insights into stem cell regulation and miRNA function. Understanding how stem cells are maintained and terminated in plants will help derive basic principles that govern stem cell biology and contribute to the ultimate use of stem cells in regenerative medicine. Due to the highly conserved mechanisms underlying miRNA biogenesis and function between plants and animals, an advance in the mechanistic understanding of miRNA function from our work will directly impact our abilities to harness the power of small RNAs to fight pathogens and human diseases. PUBLIC HEALTH RELEVANCE: Understanding how stem cells are maintained and how they differentiate is key to harnessing the power of stem cells for regenerative medicine in the future. This research will reveal major players in the transcriptional and post-transcriptional networks that govern the temporal regulation of stem cells. This research will also advance our understanding of the mode of action of miRNAs, regulatory molecules that impact all aspects of biology and whose mis-regulation is associated with human diseases.