IOS: Interpretation of Stem Cell Promoting Transcription Factor Gradient

University Of California-Riverside, Riverside CA

Investigators

Abstract

The growing tips of plant shoots give rise to all aboveground organs, such as leaves, flowers, and fruits. To continuously develop these organs throughout their lives, plants must maintain pools of stem cells - i.e., cells with the capacity to adopt numerous possible fates. Despite the differentiation of these stem cells into unique above-ground organs, these stem cell pools remain relatively constant. Precisely how plants (and other organisms) manage this delicate balance of stem cell maintenance and differentiation remains an important outstanding question in the field of biology. To further address this question, this project will use gene manipulation methods, biochemical analyses, and high-resolution live imaging to precisely describe how the gene expression processes that regulate this balance are controlled in plant stem cells. Understanding this delicate balance of stem cell maintenance and differentiation will facilitate the development of crop plants with optimal biomass and grain yield, as well as broadly provide new paradigms for gene regulation. Additionally, the dynamic live imaging of gene expression will be integrated into an outreach campaign aimed at explaining inquiry-based scientific learning techniques to high school students from lower income and Latino-dominated local area schools (http://cybersam.ucr.edu/Plone/lab-outreach-2). The project will additionally train a postdoctoral fellow, a graduate student and several undergraduate students in methods and principles of gene regulation in actively developing tissues. In Arabidopsis, WUSCHEL (WUS), a stem cell promoting transcription factor, moves from the rib meristem (RM) into the stem cell domain/central zone (CZ) where it represses transcription of differentiation promoting transcription factors and activates transcription of its own negative regulator-CLAVATA3 (CLV3) by directly binding the promoters. How WUS manages to activate CLV3 at a distance from the RM, and how it activates some genes and represses others is not understood. Unpublished work from the Gonehal Lab reveals that WUS binds several closely spaced cis-elements with different affinities (a cis-regulatory module [CRM]) in the CLV3 enhancer region as monomer and as dimer at lower and higher protein concentrations, respectively. The in vivo cis-element manipulations and manipulation of the WUS protein levels reveal that WUS utilizes the CRM to repress CLV3 at higher WUS concentration in the RM and activate at lower concentration in the CZ. This work aims to understand the regulation of spatio-temporal precision of CLV3 expression by understanding the mode and mechanism of action of the CLV3 CRM, characterize WUS binding cis-elements in a gene repressed by WUS and understand mechanisms of concentration-dependent transcriptional discrimination through functional analysis of putative co-factors that interact with WUS. This activity will lead to a new paradigm in transcriptional regulation in plants and in concentration-dependent transcriptional regulation in general. Insights obtained from this work will facilitate comparative analysis of transcriptional regulation in shoot and root stem cell niches.