Dissecting the Molecular Pathways that Coordinate Lateral Root Initiation with Environmental Signals

植物完全依赖于它们附近可用的资源。不幸的是，营养物质的可用性和分布在环境中是不断变化的。植物必须能够感知这些变化并做出适当的反应。这种发育可塑性在植物根系中可以明显观察到。根系是一个高度分支的结构，从土壤中提取水分和养分。侧根的数量和位置都受到环境因素的显著影响。这使得植物能够优化其根系以适应其独特的栖息地，有效地竞争土壤资源并在不利条件下生存。侧根由母根成熟的中柱鞘细胞形成。我们几乎不了解中柱鞘细胞是如何被触发重新进入细胞周期并重新分化以产生侧根原基的。同样，对于某些中柱鞘细胞是如何在邻近细胞处于静止状态时被选择增殖的，我们所知甚少。最后，外界条件是如何被感知的，以及这些信息是如何被整合到决定新的侧根将在何时何地形成的，这些都是不清楚的。本提案的目的是剖析调节侧根起始的机制。我们的主要策略包括分析我们最近从拟南芥中分离出的侧根起始突变体lin1。野生型拟南芥在某些环境条件下会显著抑制侧根的形成，而lin1突变体则保持了高度分枝的根系。此外，lin1显示了生长素积累模式的改变，生长素是一种已知对侧根形成至关重要的激素。我们将克隆LIN1基因，并利用遗传学、生理学和基因组学方法对LIN1通路进行表征。这些研究将开始揭示植物生物学中的一个基本谜团：如何做出决定来协调植物的发育与环境线索？它们还将影响我们对植物在营养生长过程中如何能够选择性地激活细胞增殖和器官发生的理解。通过关注根系，我们的工作也将为植物适应水分和养分胁迫提供重要的见解，并可能导致能够在不利条件下生存的作物的发展。

Plants are completely dependent on the resources that are available in their immediate vicinity. Unfortunately, nutrient availability and distribution are in constant flux in the environment. Plants must be able to sense these changes and respond appropriately. This developmental plasticity can be clearly observed in the plant root system. The root system is a highly branched structure that extracts water and nutrients from the soil. Both the number and placement of lateral roots are dramatically affected by environmental cues. This allows the plant to optimize its root system to its unique habitat, compete effectively for soil resources and survive adverse conditions. Lateral roots are formed from mature pericycle cells in the parent root. We have almost no understanding of how pericycle cells are triggered to re-enter the cell-cycle and re-differentiate to create the lateral root primordium. Similarly, very little is known about how certain pericycle cells are selected to proliferate while their neighbors remain quiescent. Finally, it is unclear how external conditions are sensed and the information integrated into decisions about where and when a new lateral root will be formed. The objective of this proposal is to dissect the mechanisms that regulate the initiation of lateral roots. Our main strategy involves the analysis of a lateral root initiation mutant, lin1, that we have recently isolated in Arabidopsis thaliana. While wild-type Arabidopsis plants drastically repress lateral root initiation under certain environmental conditions, the lin1 mutant maintains a highly branched root system. Furthermore, lin1 shows altered patterns of accumulation of auxin, a hormone known to be critical for lateral root initiation. We will clone the LIN1 gene and characterize the LIN1 pathway using genetic, physiological and genomic approaches. These studies will begin to shed light on one of the fundamental mysteries in plant biology: How are the decisions made that coordinate plant development with environmental cues? They will also impact our understanding of how plants are able to selectively activate cell proliferation and organogenesis during vegetative growth. By focusing on the root system, our work will also provide important insights into plant adaptation to water and nutrient stress and may lead to the development of crops able to survive under adverse conditions.