Regulatory Systems Controlling Plant Cell Axis Formation and Regenerative Stem Cell Formation

在多细胞生物中，细胞获得不同的细胞命运以形成功能上有意义的身体模式的分子机制，称为生物模式形成，在很大程度上仍然未知。对模式形成的更好的分子理解对于避免大多数多细胞生物，特别是植物中计划外的癌细胞增殖，以及优化生长，资源分配，某些类型的抗逆性，从而提高产量非常重要。产量的提高反过来又与世界生态、经济和人类发展的利益有关。理解模式形成的一个关键组成部分是确定定义各种干细胞壁龛的精确分子决定因素。特别是在植物中，我们对干细胞生态位形成的分子认识不足严重阻碍了育种和生物技术，因为它使许多农学上非常重要的植物物种难以进行体外再生，而体外再生是无性繁殖、性状大规模评估、濒危物种拯救和转化的先决条件。近年来，为了更好地理解模式形成，在许多模式生物中取得了重大进展，主要基于遗传方法，其次是大规模基因组学和靶向分子策略。在植物中，这些方法已经融合在多细胞模式与单个植物细胞极性获取的迷人细胞生物学互连中。事实证明，大量看似独立的模式过程，包括胚胎轴的形成，顶端分生组织的内部组织，芽和根的侧枝器官的形成，甚至叶根形成和维管模式的形成，都可以归因于一个单一的简单分子，吲哚乙酸（IAA，一种生长素“植物激素”）通过单个细胞的极性运输和反馈控制分布。生长素被感知并翻译成基因调控反应，包括通过生长素反应（转录）因子（ARFs）及其Aux/IAA家族的核共调节因子控制其运输(1)。基于对生长素转录调控基因的广泛研究，本提案概述了以下策略：(a)使用特定的遗传开关来显著提高植物再生特性以及干细胞在侧分生组织中的活性；(b)基于小化合物筛选的结果分析控制植物干细胞特性的其他途径。(c)通过一种新型的ARF变异，继续揭示ARF- aux /IAA调控网络的功能基因组学；(d)基于已确定的数量性状位点，确定控制血管细胞特性的新调控因子。

The molecular mechanisms by which cells in multicellular organisms acquire distinct cell fates to form functionally meaningful body patterns, termed biological pattern formation, are still largely unknown. A better molecular understanding of pattern formation is important for avoidance of unscheduled cancerous cell proliferation in most multicellular organisms and specifically in plants also for optimized growth, resource allocation, certain types of stress resistance and hence improved yield. Yield improvements, in turn, are associated with benefits for the world’s ecology, economy and human development. A critical component in understanding pattern formation is the identification of the precise molecular determinants that define various stem cell niches. Specifically in plants, our insufficient molecular insights into stem cell niche formation has severely handicapped breeding and biotechnology, as it has kept many agronomically highly important plant species recalcitrant to in-vitro regeneration, a prerequisite for vegetative propagation, mass assessment of traits, rescue of endangered species and transformation. In recent years, significant progress to better understand pattern formation has been made in a number of model organisms, predominantly based on genetic approaches followed by large-scale genomic and targeted molecular strategies. In plants, these approaches have converged in the fascinating cell-biological interconnection of multicellular patterning with polarity acquisition of the individual plant cell. As it turned out, a huge number of seemingly separate patterning processes, including embryo axis formation, internal organization in both apical meristems, the formation of lateral organs in shoots and roots and even phyllotaxis and vascular patterning could be attributed to the polar transport and feed-back controlled distribution of a single simple molecule, indole-acetic acid (IAA, an auxin "phytohormone”) through individual cells. Auxin is perceived and translated into gene-regulatory responses, including those controlling its transport by Auxin Response (transcription) Factors (ARFs) and their nuclear co-regulators of the Aux/IAA family (1). Based on extensive work with the auxin transcriptional regulation genes, this proposal outlines strategies to (a) use specific genetic switches to dramatically increase plant regeneration properties as well as stem cell activities in lateral meristems, (b) analyze other pathways controlling stem cell properties in plants based on the results of small compound screens, (c) continue to unravel the functional genomics of the ARF-Aux/IAA regulatory network through a novel type of ARF variants and (d) identify novel regulators controlling vascular cell properties based on identified Quantitative Trait Loci.