The Angiosperm Sieve Tube System: Elucidating Gene Regulatory Networks Involved in Phosphate Acquisition & Homeostasis

在未来的几十年里，我们的全球社会将面临一个重大的挑战，即实现足够的农业生产来维持不断增长的人口，改变食物偏好和增加对生物燃料的生产需求。这一挑战既要求大幅度提高粮食总产量，同时又要求在养分和水分供应受限的情况下维持作物产量。在这方面，磷(P)是所有植物和动物的主要常量营养素需求，将是增加全球粮食生产的主要挑战。这一挑战的基础是双重的。首先，土壤中含有各种形式的磷，包括无机磷和有机磷，在许多农业土壤中，低水平的有效磷限制了一般生物质生产和作物产量潜力。现代农业实践试图通过以肥料的形式施用磷来克服这一问题，这种方法对产量的增加作出了重大贡献。然而，全球可获得的磷资源是有限的，并且正在迅速减少。第二，现代作物品种的培育是以牺牲磷利用效率为代价来提高产量的。因此，为了确保未来农业生产力的高（和增加）水平，植物科学家必须更好地了解控制植物体内磷稳态的分子事件。目前的研究正在解决植物根系所采用的机制，以搜索和挖掘土壤环境中各种可用形式的磷。在这个项目中，重点将放在确定植物所采用的内部信号系统的分子基础上。这使得土壤与根和芽器官之间产生互动反应，以优化磷的获取和分配，在土壤中磷有效度有限的情况下支持生长（和产量）。所产生的知识将补充其他研究小组的工作，这些研究小组将共同成为基于基因组学的育种计划的关键资源，其最终目标是在减少磷肥施用的情况下开发具有增强生长能力和高产潜力的农作物。实现这一目标将有助于确保满足所有国家人民的营养需要。所有生成的数据都可以通过项目网站和长期存储库访问。生产足够的粮食来维持不断增长的人口是具有挑战性的，因为需要在磷酸盐（Pi）肥料可用性将成为限制条件的情况下这样做。要解决这些问题，就需要开发具有更高Pi利用效率的作物。在这方面，人们早就知道根系对磷的吸收是由根到茎（木质部）和枝到根（韧皮部）信号控制的。然而，在这些血管信号通路中起作用的分子成分仍然知之甚少。本项目旨在确定这些信号的性质，这些信号在协调植物对Pi的吸收和利用中起作用。这些研究将涉及利用功能基因组学、计算生物学、细胞、生理和蛋白质化学方法，以解决以下目标：(a)确定位于源叶片内的pi感应细胞；(b)确定哪些pi上调的韧皮部汁液RNA物种移动到根/茎尖；(c)鉴定根/茎尖内接收和响应这些韧皮部RNA的细胞。这些知识将补充其他小组正在进行的努力，并为旨在提高植物Pi利用效率的基于基因组学的育种计划奠定基础。

In the coming decades, our global society will face a significant challenge in terms of achieving agricultural production sufficient to sustain the expanding population, changing food preferences and increasing production demands for biofuels. This challenge represents both a need for a substantial increase in overall food production and, at the same time, sustaining crop yields under conditions where nutrient and water availability will serve as limiting conditions. In this regard, phosphorus (P), a major macronutrient requirement for all plants and animals, will represent a major challenge for increasing global food production. The basis for this challenge is two-fold. First, soils contain P in various forms, including inorganic (Pi) and organic phosphates, and in many agricultural soils, low levels of available P place constraints on general biomass production and crop yield potential. Modern agricultural practice has sought to overcome this problem through application of P, in the form of fertilizer, and this approach has contributed substantially to yield increases. However, global available P resources are finite and rapidly being diminished. Second, modern crop species have been bred for increased yield at the expense of P use efficiency. Thus, to ensure future high (and increased) levels of agricultural productivity, plant scientists must develop a better understanding of the molecular events involved in controlling P homeostasis in plants. Current studies are addressing the mechanisms employed by the root system of the plant to search and mine the soil environment for the various available forms of P. In this project, a focus will be placed on identifying the molecular basis of the internal signaling systems, employed by plants, that allows for an interactive response between the soil and the root and shoot organs to optimize P acquisition and allocation to support growth (and yield) in the presence of limited P availability within the soil. Knowledge generated will complement work by other research groups that, collectively, will serve as a pivotal resource for genomics-based breeding programs, with the ultimate goal of developing agricultural crops with enhanced ability for growth and high yield potential under reduced Pi fertilizer application. Achieving this goal would help to ensure that the nutritional needs are met for the peoples of all countries. All data generated will be accessible through a project website and through long-term repositories. Producing sufficient food to sustain an expanding population is challenging because of the need to do so under conditions where phosphate (Pi)-fertilizer availability will become a limiting condition. Achieving a solution to these problems will require the development of crop plants with enhanced Pi use efficiency. In this regard, it has long been known that Pi uptake by the root system is controlled by root-to-shoot (xylem) and shoot-to-root (phloem) signaling. However, the molecular components that function in these vascular signaling pathways remain poorly understood. This project aims to identify the nature of these signals that function in coordinating Pi uptake and utilization by the plant. These studies will involve the utilization of functional genomics, computational biology, cellular, physiological and protein chemistry approaches, to address the following objectives: (a) identify the Pi-sensing cells located within source leaves; (b) determine which Pi-upregulated phloem sap RNA species move to the root/shoot apex; and (c) identify cells within the root/shoot apex that receive and respond to these phloem RNA species. This knowledge will complement ongoing efforts by other groups and establish a foundation for genomics-based breeding programs aimed at improving plant Pi use efficiency.