Regulation of the Orientation of Cell Expansion in Plants

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The long term goal of this project is to understand the molecular mechanisms that regulate the orientation of cell expansion. The shape of plant organs depends heavily on the ability of cells to direct expansion in specific orientations. The quality of agricultural products such as cotton is dependent on highly oriented cell expansion. A genetic analysis of cell expansion in the root of Arabidopsis has identified mutants with abnormally oriented expansion. Of particular interest is the cobra mutation which results in cells that appear to expand radially rather than longitudinally. A detailed analysis of the cobra phenotype led to the hypothesis that the COBRA gene product regulates the transition from radial to longitudinal expansion. The COBRA gene has been positionally cloned and its deduced amino acid sequence indicates that the COBRA protein is anchored to the plasma membrane and that a portion of the protein could interact with the cell wall. Evidence that COBRA activity is regulated at the transcriptional level comes from the finding that there are increased levels of COB RNA in root cells that are undergoing the transition from radial to longitudinal expansion. The goal of this proposal is to test the hypothesis that COBRA is a regulator of oriented cell expansion and to use COBRA to characterize the molecular mechanisms by which oriented cell expansion is controlled. This will be done by determining the normal expression and localization of COBRA RNA and protein and by analyzing the effects of altering these expression patterns. COBRA will then be used as the starting point to build an understanding of the molecular interactions that regulate oriented cell expansion.