Cell division is a central event in the development of all multicellular organisms but it is especially important for plant development. Because plant cells are surrounded by a rigid cellulose cell wall that renders them incapable of movement, the spatial and temporal patterns of cell division play a central role in defining the ultimate architecture of the organism. Cell division is the result of two main events; first the accurate partitioning of the genetic material during nuclear division, then the partitioning of the cytoplasm and its contents during cytokinesis. Plants partition their cytoplasm by building a new cell wall from the inside-out between the two sets of daughter chromosomes. While the events of plant cytokinesis, especially as it occurs in somatic cells and during endosperm cellularization, are known in detail at an ultrastructural level, our understanding at the molecular level is quite limited. Furthermore despite the striking differences between cytokinesis in plants and animals, recent studies have revealed a common requirement for membrane trafficking. Consequently insights into the cellular mechanisms of plant cytokinesis are likely to shed light on vesicle trafficking events that occur during cytokinesis in both plant and animal cells. The focus of this proposal is on patellin 1, a novel Arabidopsis Sec14-like phosphoinositide-binding protein, we originally identified in a screen for membrane-associated F-actin-binding proteins. Patellin 1 is found associated with punctate cytoplasmic structures and localizes during cytokinesis to the expanding and maturing cell plate. Based on its localization, biochemical properties, and sequence similarity to Sec14p (a Saccharomyces cerevisiae protein that is essential for secretion) and GOLD domain membrane trafficking proteins we hypothesize that patellin 1 plays a critical role in membrane trafficking events during plant cytokinesis. The specific aims are to: 1) determine if patellin 1 play an essential role in plant cytokinesis by characterizing T-DNA insertion knock-out mutants, 2) determine if patellin 1 interacts with known proteins of the secretory machinery by identifying and characterizing interacting proteins using affinity binding, coimmunoprecipitation and yeast two-hybrid approaches and 3) characterize the dynamic behavior of patellin 1 during cytokinesis by confocal imaging of patellin 1 ::GFP fusions in transformed BY2 cell lines and and Arabidopsis plants, as a means of better defining patellin 1's role in membrane traffic during cell plate development. Completion of the specific research aims will provide insight into the cellular role of patellin 1 during the maturation stage of cytokinesis.