Protein targeting to the chloroplast outer membrane and Toc complex assembly and function

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Eukaryotic cells are sub-divided into numerous membrane-bound organelles that provide specialized environments for many biochemical pathways that are indispensable for survival. The cells of plants are distinguished from most other eukaryotes by the presence of a class of essential organelles called plastids. The most well-known plastids are chloroplasts, which house the reactions of photosynthesis, a process upon which all life depends. The vast majority of proteins found within each organelle are encoded by genes in the nucleus and are translated in the cytosol. Cells therefore rely on protein trafficking systems to ensure these proteins are delivered to their proper sub-cellular compartment. Although targeting systems have been described for all organelles, the mechanisms of protein recognition and translocation are not well understood. The long-term goal of my research program is to contribute to the understanding of the mechanism of protein targeting and import into chloroplasts, as a model for intracellular protein trafficking and organelle biogenesis in all eukaryotes, and as it pertains to plant growth and development. Protein import into chloroplasts relies on proteinaceous complexes located at the double membrane that surrounds the organelle. The focus of my research program is to understand how the chloroplast protein import apparatus is assembled at the chloroplast surface, and how the precision of protein import is achieved by these translocons. We will use a combination of molecular, biochemical and biophysical approaches to complement in vivo approaches to answer these questions. Specifically, we will investigate how proteins are targeted to the chloroplast outer membrane, how complexes responsible for initiating import into chloroplasts are assembled, and determine the basis for their substrate specificity. Detailed knowledge of how proteins are imported into chloroplasts is important for understanding photosynthesis and plant growth and development. Furthermore, the work will contribute to our overall understanding of intracellular protein trafficking, which is a fundamental cellular process essential for the growth and survival of all organisms.