Specialized cell types allow plants to shed their structures-such as leaves, flowers and fruit-through a carefully orchestrated process of cell separation. Surprisingly little is known about the genetic pathways that underlie the cellular differentiation of separation zones, their responses to the hormones ethylene and auxin, and the vesicle trafficking and enzyme secretion necessary for cell separation. The research focus of the Liljegren lab is to investigate the molecular mechanisms that control cell separation using the Arabidopsis flower as a model system. As in many other higher plants, Arabidopsis flowers contain pattern elements which allow distinct separation events such as floral organ shedding, fruit opening, and seed dispersal to take place during their life cycle. Through genetic approaches, we and our colleagues have identified key transcriptional regulators-the redundant SHATTERPROOF MADS-box genes and a novel bHLH gene, INDEHISCENT-that control differentiation of the separation zones essential for fruit opening. Currently, we are characterizing the functions of several genes required for floral organ shedding, including NEVERSHED, LOVES-ME-NOT and STAMENSTAY. We have recently discovered that NEVERSHED regulates vesicle trafficking during flower development and are now using sensitized screens to identify additional components of a pathway that likely controls the movement and secretion of specific molecules during the shedding process.