Collaborative Research: Regulation of exocytic membrane trafficking required for cytokinesis and polarized cell expansion

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The plasma membrane is the outer membrane of all cells that regulates the entry and exit of material between the inside of the cell and its environment. In plants, the plasma membrane is surrounded by a cell wall that provides additional mechanical strength and protection. Production of large amounts of new plasma membrane and cell wall material is essential for plant cell division and expansion. In addition, regulation of the activity, distribution, and abundance of proteins located at the plasma membrane is highly critical for numerous cellular processes essential for growth and health of plants, including nutrient uptake, hormone signaling, pathogen perception, stress responses, and construction of the cell wall. This project will focus on understanding how the delivery of material required for plasma membrane formation and maintenance is controlled in dividing and expanding cells. Broader Impact activities include the intrinsic merit of the research as it is expected that the information gained in these studies will lead to the development of new tools and strategies for enhancing yield and quality of crop plants necessary for food security and energy independence through the improved production of biofuels and other agronomically important products. In addition to its economic and scientific benefits, this project will also provide important research training for young scientists at the undergraduate and graduate level. Students involved in this project will receive advanced training in the areas of biochemistry, genetics, and microscopy fundamental to modern cell biology research.In plants, the multisubunit SCD complex is essential for the delivery of membrane, proteins, and cell wall material to the plasma membrane by a process known as exocytosis. Major subunits of the SCD complex include the DENN domain-containing protein, SCD1 (stomatal cytokinesis defective1) and the coiled-coil protein, SCD2, which have previously been shown to be necessary for membrane trafficking required for cytokinesis and cell growth in Arabidopsis thaliana. Additionally, biochemical studies have identified another subunit of the SCD complex, MyTH1, which is related to the membrane-binding domain of metazoan class I myosins. Homologs of SCD complex subunits are present in land plants and green algae as well as other eukaryotes but were lost in yeast and metazoans, suggesting that the SCD complex is of ancient evolutionary origin. The specific aims of this project are to 1) define the biochemical activity and regulation of the SCD complex, 2) delineate the network of protein-protein and protein-lipid interactions that govern SCD complex assembly and membrane association required for exocytic membrane trafficking and 3) perform comparative studies of SCD1, SCD2, and MyTH1 homologs in the model systems Arabidopsis and Physcomitrium (Physcomitrella) patens. These combined approaches will provide insights into critical conserved and divergent functions of SCD complex subunits, necessary for exocytic trafficking, extending across the evolutionary distance between angiosperms and bryophytes. In addition, as the mechanisms of exocytosis have to date been primarily studied in yeast and metazoan model systems lacking the SCD complex, this project will generate fundamental knowledge of the exocytic molecular machinery of other plants and eukaryotes, which are important for the diversity and health of marine, freshwater, and terrestrial ecosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.