Regulation of Shoot Development by the Maize Meristem

高等植物的茎尖分生组织在植物的整个生命周期中，最终负责在胚胎后向茎部添加新的细胞、组织和器官。在营养发育过程中，分生组织以重复的方式产生叶片和茎组织。随着营养发育的进展，新形成的器官分化的方式可能会发生变化，这一过程称为相变。一旦进入生殖阶段，茎分生组织形成或成为花分生组织，这启动了一个可预测和确定的花器官序列。关于营养芽顶端分生组织的功能，如如何启动侧枝器官，在多大程度上决定侧枝器官如何分化，以及营养分生组织如何召集成花序或花的分生组织，仍有许多有待研究。本文提出的研究重点是探讨是什么控制着茎尖发生的各种发育过程。实验将在玉米植株上进行，并将利用我们为玉米开发的茎部分生组织培养技术。我们之前的分生组织培养实验表明，从营养发育到生殖发育的变化和相变过程都受到整个植物发生的全局信号的控制。我们提出了一组实验，旨在了解玉米的全球信号是如何与分生组织自主活动协调的。将讨论以下问题：玉米向开花过渡所需的不确定基因的表达如何受到培养诱导的茎尖重置的影响？2. 当分生组织被迫经历长时间的营养发育时，它是如何重组的？3. 当一个成年分生组织被分离并形成一个完整的新芽时，所有的阶段特异性表型是否都被重置？如果在特定基因（PI-Blotched）中发生重置，该位点的甲基化状态如何受到影响？4. 在幼年期延长和繁殖延迟的突变背景下，这种较慢的个体发育是由于来自叶片原基的信号改变（较弱）的结果吗？异时突变的表达依赖于植物的生长阶段，还是依赖于萌发后1分钟的自由运行测量？这些问题的答案将增加我们对茎个体发育过程中发生的全局变化的理解，以及茎分生组织（器官发生的部位）在指导这些变化中的作用。

Irish 9728518 The shoot apical meristem of higher plants is ultimately responsible for the post-embryonic addition of new cells, tissues, and organs to the shoot through-out the life of the plant. During vegetative development, the meristem initiates leaves and stem tissue in a repetitive manner. As vegetative development progresses, the manner in which newly formed organs differentiate may vary, in a process termed phase change. Once in the reproductive phase, shoot meristems form or become floral meristems, which initiate a predictable and determinate sequence of floral organs. Much remains to be learned about the functioning of the vegetative shoot apical meristem, such as how it initiates lateral organs, to what extent it determines how those organs differentiate, and how the vegetative meristem is convened to an inflorescence or floral meristem. The focus of the research proposed here is to ask to what controls various developmental processes that occur at the shoot apex. The experiments will be conducted using the maize plant, and will take advantage of a technique, shoot meristem culture, that we have developed for maize. Our previous experiments using meristem culture indicated that both the change from vegetative to reproductive development and the process of phase change are under the control of global signaling that occurs throughout the plant. We propose a set of experiments that are aimed at understanding how global signaling in maize is coordinated with meristem-autonomous activities. The following questions will be addressed: 1. How is the expression of indeterminate, a gene required for the transition to flowering in maize, affected by the culture-induced resetting of a shoot apex? 2. How is the meristem reorganized when it is forced to undergo a prolonged period of vegetative development? 3. Are all phase-specific phenotypes reset when an adult meristem is isolated and forms a complete new shoot? If resetting occurs in a specific gene (PI-Blotched), how is the methylation state of that locus affected? 4. In mutant backgrounds in which the juvenile phase is prolonged and reproduction delayed, is this slower ontogeny the result of altered (weaker) signaling from leaf primordia? Is the expression of heterochronic mutations dependent on the phase of the plant, or on a free-running measurement o1' time after germination? The answers to these questions will increase our understanding of the global changes that occur during shoot ontogeny and the role of the shoot meristem, the site of organogenesis, in directing these changes.