Specialized cell types allow plants to shed entire organs—such as leaves, flowers and fruit—through a carefully orchestrated process of cell separation (abscission). Although abscission has been a topic of scientific curiosity since the days of the Greek botanist Theophrastus, and classic experiments carried out during the past century demonstrated its regulation by the plant hormones ethylene and auxin, very little is known about the pathways that direct cellular differentiation of separation zones, their response to hormones, and the vesicle trafficking and enzyme secretion necessary for cell separation. The research focus of the Liljegren lab is to investigate the molecular mechanisms controlling cell separation in the Arabidopsis flower. 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 forward and reverse 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 fruit-specific separation zones essential for Arabidopsis fruit opening. We are currently characterizing the function of NEVERSHED, a gene required for floral organ-specific shedding and mapping mutations in two additional genes—LOVES-ME-NOT and STAMENSTAY—that prevent floral organ separation. Since many genes involved in plant cell separation will likely be missed in traditional mutant screens due to widespread genetic redundancy, we are also pursuing novel approaches to survey the expression profiles of separation zone cells and identify genes that may control their differentiation and response to hormone signaling. Future functional studies of these candidate genes will allow us to continue uncovering the intersecting pathways that control this remarkable biological process.  |
