Deciphering the Golgi Apparatus: From Imaging to Genes

The Golgi apparatus is a vital organelle in eukaryotic cells. It grabs and processes secretory materials synthesized by the endoplasmic reticulum (ER) before sorting them to their destination. The Golgi also receives materials from vacuoles/lysosomes and the plasma membrane for further recycling to other compartments within the cell (1) ( Figure 1 ). Given the vital role of the Golgi in a cell, it is important to understand how this organelle attains and maintains its structural and functional integrity during the intense processes of membrane traffic. Despite an equally central role of the Golgi in membrane traffic in eukaryotes, the organization of this organelle has some unique features in each cell system. Therefore, the wealth of information available on the structure and activity of the Golgi in one system is not always directly transferable to others. However, certain morphological and functional aspects are common among cell systems. Therefore, studying the factors that regulate organelle biogenesis and organization of the Golgi apparatus is important in basic cell biology of eukaryotes and may also contribute to a better understanding of how different cell systems have evolved. In this study, we report on the identification of Golgi mutants in plant cells. We have developed a screen that is a promising strategy not only for the identification of genes responsible for the morphological and functional integrity of the plant Golgi but could also provide fundamental information on other multicellular systems for which the power of forward genetics cannot be exploited as easily as in Arabidopsis. The Golgi occupies a central role in membrane traffic. A) Schematic representation of trafficking pathways in a plant cell (reviewed in 1 ). (a) Anterograde and retrograde protein transport from the ER to the cis Golgi and back. Proteins leaving the Golgi may have different destinations: some will be directed to the lytic (b) or protein storage vacuole (PSV, c), others will reach the plasma membrane (PM, d). The Golgi also receives retrograde flow of proteins from the PM (d). The Golgi appears to be also involved in a transport route to the chloroplast (28) (e). B) Confocal microscopy image of a tobacco leaf epidermal cell expressing the known ER/Golgi marker, ERD2–GFP (3) , and an ER membrane marker, yellow fluorescent protein–Vap (unpublished data). A Golgi stack and an ER tubule are labeled with an arrowhead and an arrow, respectively. Scale bar = 5 μm.