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Discovering the mechanism of transcription factor-controlled cell size

Reference	BB/G019894/2
Principal Investigator / Supervisor	Professor Liam Dolan
Co-Investigators / Co-Supervisors
Institution	University of Oxford
Department	Plant Sciences
Funding type	Research
Value (£)	447,097
Status	Completed
Type	Research Grant
Start date	01/01/2010
End date	31/12/2012
Duration	36 months

Abstract

Cell growth is regulated during the development of unicellular and multicellular organisms and is a key determinant of organism morphology. We discovered a master regulator of root hair cell growth in Arabidopsis thaliana called RSL4. The aim of this research proposal is to determine the role of the RSL4 in the control of root hair growth. The disappearance of RSL4 determines the time at which root hair growth stops. To investigate how cells control the time at which they stop growing we propose to characterise the mechanism by which RSL4 is removed from hair cells. We will characterise the role of the Destruction-box in RSL4 in the removal of this protein from hair cells as growth ceases. To identify proteins required for the removal of RSL4 we will carry out a mutant screen to identify mutant plants in which RSL4 destruction is defective resulting in the formation of long root hairs. Characterisation of these genes will define the mechanism by which RSL4 is removed from the cell and by extension how cells stop growing. We hypothesise that environmental signals and stresses control growth by increasing RSL4 transcription and the duration during which RSL4 is present in cells. We will test this hypothesis directly and use genetic approaches to verify our results. This will provide a mechanistic insight into the mechanism by which environmental factors modulate an endogenous developmental pathway. Given that RSL4 is sufficient to control root hair growth we predict that RSL4 controls the transcription of genes that effect growth. We will identify these genes using a variety of techniques including chromatin immunoprecipitation coupled with micro array analysis. This will not only identify key players in the growth process but it will also show how these genes are regulated by RSL4. These experiments will define a novel mechanism of growth control and provide tools to generate crop plants with enhanced nutrient uptake efficiency.

Summary

We discovered a master regulator of root hair cell growth in Arabidopsis thaliana called RSL4. Root hairs are important for the uptake of nutrients from the soils such as phosphate and iron and breeding plants with long root hairs has led to the development of cultivars of beans that have higher yields that conventional cultivars. Therefore understanding the mechanism of RSL4-mediated root hair growth is an important goal for enhancing crop yields but also offers the opportunity to understand the fundamental biological processes of cell growth. Our preliminary characterisation of the role of RSL4 in root hair growth gives rise to three hypotheses that we will test in the proposed research: 1. We predict that the presence of RSL4 in a cell confers growth potential and its subsequent removal signals the cessation of growth. Put another way it means that growth occurs when RSL4 is present in the cell and then when RSL4 protein disappears growth ceases. We will test this hypothesis and identify proteins that are required for the destruction of RSL4 protein. 2. We predict that when environmental factors modulate root hair growth they do so by changing the abundance of RSL4 protein in the root hair cell. Growing plants in low phosphate causes plants to produce longer root hairs allowing the plant to mine more soil for this valuable nutrient. We predict that low phosphate increases root hair length by increasing the levels and the time at which RSL4 is present in root hair cells. 3. We predict that RSL4 regulates the expression of genes that are involved in root hair cell growth. We will identify the genes that are regulated by RSL4 and determine their role in growth. This will identify a set of genes involved in root hair growth. These proposed experiments will define a novel mechanism of growth control and provide tools to generate crop plants with enhanced nutrient uptake efficiency.

Committee	Closed Committee - Genes & Developmental Biology (GDB)
Research Topics	Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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