Presenter: Jeffery M. Kimbrough 
Advisor(s): Heike Winter Sederoff  
Author(s): Jeffery M. Kimbrough, Raul Salinas-Mondragon, Christopher Brown and Heike Winter Sederoff
Graduate Program: Botany 

Title: Fast and Transient Transcriptional Regulation of Gravitropism in A. thaliana Root Tips  

Abstract: Plant roots sense changes in their orientation towards the vector of gravity and mechanical stimulation, which ultimately leads to a differential growth response. To understand the regulation of gene expression involved in gravitropism, we carried out a time-course analysis of whole genome transcript abundance changes throughout the first hour of gravitropic and mechanical stimulation in the Arabidopsis root apices using microarray technology. Rapid, transient changes in the relative abundance of specific transcripts occurred in response to gravity and mechanical stimulation. Our results indicate both the relative abundance and timing of events are important for establishment of gene expression cascades for either stimulus (Kimbrough et al., 2004).
A novel lipid binding domain protein encoding gene was significantly up-regulated within 1 minute following gravity stimulation in the Arabidopsis root tips. We have shown that its transcription is mediated by the signaling molecule IP₃ , and that it is specifically expressed in the root tip as both a transcript and a protein. Transgenic plants over-expressing this gene/protein exhibit a lethal phenotype. Further functional characterization of this gene and its family will give new insights into signal transduction elements and pathways involved in root gravitropism and their integration with other stress responses.