Exploring lateral root formation in the context of a 'clock and wavefront' model

描述（由申请人提供）：周期结构是在不同生物系统的发育过程中形成的。本提案的主要目的是在脊椎动物体体周期性形成的“时钟-波前”模型建立的框架内，研究植物侧根（LRs）的周期性形成。体细胞发生模型提出，一个移动的分子振荡器，即分割时钟，设定了体细胞形成的周期。时钟信号通过与“波前”两个相反的信号梯度的相互作用转化为周期性片段的空间模式，在“波前”，细胞变得有能力形成响应时钟信号的体。这种“时钟-波前”机制解释了沿脊椎动物轴的体的周期性序列形成。在根中也发现了一个移动的分子振荡器，它的破坏改变了LR的形成。此外，在根中已经预测到一种激素梯度，我们有证据表明存在第二种梯度。我们提出“时钟-波前”机制可能是多种多细胞真核生物形成周期结构的共同调控策略。为了验证我们的假设，即“时钟和波前”机制在LR开发中起作用，我们将解决三个具体目标。振荡的行为将被检验并建立数学模型。我们将检验类维生素a梯度在根中起作用的假设，并检验梯度与振荡的相互作用。此外，LR形成的自然变异将用于识别参与这一过程的基因。分析荧光素酶在转基因植物中形成的振荡和梯度的主要方法是荧光素酶报告基因的实时成像。振荡的响应和随后形成LR的能力将通过化学和分子生物学方法对梯度进行操作来检查。这些实验的结果将用于建立振荡行为及其与梯度相互作用的数学模型。最后，通过关联研究和数量性状位点分析，利用LR形成的自然变异来鉴定参与这一过程的基因。这些研究构成了一种分析LR发展的新方法，并将揭示LR周期性是如何建立和维持的基本问题。

DESCRIPTION (provided by applicant): Periodic structures are formed during development in diverse biological systems. The main objective of this proposal is to examine the periodic formation of lateral roots (LRs) in plants, within the framework established by the 'clock-and-wavefront' model for the periodic formation of somites in vertebrates. The model for somitogenesis proposes that a traveling molecular oscillator, the segmentation clock, sets the period of somite formation. The clock signal is translated into a spatial pattern of periodic segments by interaction with two opposing signaling gradients at the 'wavefront', which is where cells become competent to form somites in response to the clock signal. This 'clock-and-wavefront' mechanism accounts for the periodic serial formation of somites along the vertebrate axis. A traveling molecular oscillator has also been identified in roots and disruption of it alters LR formation. Moreover, one hormone gradient is already predicted in the root and we have evidence implicating a second gradient. We propose that the 'clock-and-wavefront' mechanism may be a common regulatory strategy in the formation of periodic structures in diverse multicellular eukaryotes. To test our hypothesis that a 'clock-and-wavefront' mechanism is operating in LR development, three specific aims will be addressed. The behavior of the oscillation will be examined and mathematically modeled. The hypothesis that a retinoid gradient operates in the root will be tested and the interaction of the gradient with the oscillation will be examined. Additionally, natural variation in LR formation will be used to identify genes involved in this process. The primary method in analyzing the oscillation and the gradient in LR formation will be real-time imaging of luciferase reporters in transgenic plants. The response of the oscillation and subsequent competency to form a LR will be examined upon manipulation of the gradients by chemical and molecular biological methods. The results of these experiments will be used to mathematically model the behavior of the oscillation and its interaction with the gradient. Finally, natural variation in LR formation will be used to identify genes involved in this process by association studies and analysis of quantitative trait loci. These studies constitute a novel way of analyzing LR development and will reveal insight into the fundamental question of how LR periodicity is established and maintained. PUBLIC HEALTH RELEVANCE: Plant biomass is critical for all aspects of human health as it is the primary source of shelter, fiber, food, and increasingly fuel. Developing root systems that maximize utilization of the subterranean environment is key to improving all agronomically important traits and has been proposed as a mechanism to sequester excess atmospheric carbon into the soil to help mitigate global climate change. Understanding the mechanisms regulating lateral roots formation within the root system is vital to the effort to increase plant biomass, which will have broad implications on human health issues.