Discovering the mechanism of transcription factor-controlled cell size

Lead Research Organisation: University of Oxford
Department Name: Plant Sciences

Abstract

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.

Technical Summary

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.

Publications

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Description The aim of this project is to characterise the function of RSL4 in the growth of root hair cells. This is of important academic interest since we know little about the specific mechanisms that control the growth of cells in plants. It has applied importance because being able to manipulate root hair size in plants will allow the development of crop varieties with enhanced nutrient uptake abilities.

This project has demonstrated that a protein called RSL4 is a master regulator of root hair growth in Arabidopsis. Ongoing research is characterising the mechanism by which RSL4 controls growth. Preliminary evidence indicates that the proteolytic turnover of RSL4 is important for the regulation of root hair growth.
Exploitation Route Technology based on RSL genes' ability to modulate root hair growth will allow the development of crop varieties with enhanced nutrient uptake. We are trying to move this into crops. We are engaging with a technology transfer company (Plant Bioscience Ltd) to develop patented technology that is based on the ability of RSL proteins to modulate root hair length. This has led to a licensing agreement with Dow Agri-sciences with whom we are working closely.
Sectors Agriculture, Food and Drink

 
Description We have used the findings to generate wheat and rice lines with enhanced growth. These are being evaluated in field trials.
First Year Of Impact 2013
Sector Agriculture, Food and Drink
Impact Types Economic