Signal Transduction in Root Gravitropism

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

MCB0212099 PI: Gilroy, Simon PROJECT ABSTRACT Gravity is a fundamental signal that regulates plant growth and form. Despite its importance to plant success, the cellular and molecular events whereby higher plants sense and respond to this most pervasive and constant of environmental signals are essentially unknown. In the root, gravity is perceived in the columella cells of the root cap and this signal is converted to oriented growth in the elongation zone through a mechanism likely involving asymmetrical auxin redistribution. The goal of this research project is to define the cell and molecular nature of the initial gravity-related signaling events generated in the columella cells, using the roots of Arabidopsis thaliana as a model system. Previous research has identified changes in cytoplasmic and cell wall pH as important initial events in gravity signaling in the root cap columella cells. In addition, recent evidence suggests highly localized changes in Ca2+, likely close to membrane surfaces, also accompany some of the earliest events of gravity perception in these cells. Research will therefore concentrate on characterizing how these gravity-related H+ and Ca2+ fluxes are generated and how they are modulated by putative components of the gravity signal transduction system such as the actomyosin cytoskeleton. In addition, transgenic Ca2+ sensors based on the Cameleon green fluorescent protein Ca2+ sensor will be constructed and targeted to the vacuolar, endoplasmic reticulum and plasma membranes. These novel sensors will be used to assess whether membrane-associated Ca2+ microdomains are indeed associated with gravity signaling. The final goal of the research program is to develop single cell mRNA profiling for the columella cells in order to catalog gene expression patterns within the different regions of the root cap. Initial analysis will be targeted at profiling the actin and myosin gene families as these represent strong candidates for encoding parts of the force transmissive network that generates the biochemical signaling events of gravity perception. Plant growth and form are inextricably linked to the developmental impacts of gravity. Yet, despite its fundamental role in regulating development, the precise mechanism whereby plants sense and respond to gravity remains unknown. Results from this research program will therefore seek to define the molecular machinery of the root that allows it to sense gravitational forces. The project will focus on developing microscope-based imaging approaches to visualize the dynamic changes in the levels of ions that are thought to signal the gravity stimulus to the sensitive cells of the root. An understanding of these signaling events should not only help provide a more complete understanding of how plants sense and respond to their environment, but also holds the potential to uncover strategies to regulate plant development through manipulating the responsiveness of defined components of this plant gravity sensing system.