Collaborative Project: Cellular and Molecular Studies on Plasmodesmata

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The proposed research will integrate biophysical, biochemical, cellular, physiological and genetic studies on plasmodesmata (pd) to establish an appropriate framework that will then allow an investigation of the cellular processes by which the plant regulates its cell-to-cell communication system. Biophysical studies will be performed on a simple cellular system in order to determine the unitary pd conductance. Such measurements are essential for a further sub-structural analysis of the pd, as well as to provide a rigorous foundation for detailed studies on the cellular controls that orchestrate cell-to-cell size exclusion limits. Physiological studies on the role of pd in solute fluxes will also be performed. Since pd are likely to be an important determinant of organ development, an experimental system will be established that will permit identification of the processes that control secondary pd formation. In this ongoing collaboration (between Beachy and Dr. William Lucas of the University of California, Davis), it has been established that transgenic tobacco plants in which the 30 kDa movement protein (MP) of TMV is expressed have pd whose size exclusion limits are up-regulated to sizes in excess of 9.4 kDa. The mode by which the 30 kDa TMV-MP effects this change will be further explored. It is hypothesized that this protein interacts directly with the plasmodesma. Based on this concept, biochemical isolation and purification of pd proteins are proposed. A genetic system in Arabidopsis will be developed to permit the identification and isolation of genes involved in virus movement and pd function. Plasmodesmata are microscopic channels between individual plant cells. Intercellular communication by passage of molecules through these channels is critical for the normal development and physiological function of the entire plant. In certain plant viral infections, the virus gains access to the cell interior at a localized site and passes from cell to cell through the plasmodesmata throughout the plant. Passage of the virus through plasmodesmata is facilitated by a virally encoded protein which effectively enlarges the plasmodesmatal channel. This research will take advantage of the viral protein to identify and study the components of the plant plasmodesmata. Knowledge of the components of plasmodesmata will facilitate further studies of the formation of plasmodesmata and the mechanisms by which molecular traffic through the plasmodesmata is regulated. The results of this research will be important contributions to basic knowledge of cell to cell communication in plants.