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

University Of California-Davis, Davis CA

Investigators

Abstract

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.