Eukaryotic cells are organized into numerous membrane-bound organelles that segregate many of the biochemical pathways that are indispensable for survival. The cells of plants and algae are distinguished from those of other eukaryotes by the presence of a specific class of organelles called plastids. The most well-known plastids are chloroplasts, which house the reactions of photosynthesis, a process upon which all life depends. Most, if not all, proteins that comprise cellular organelles are encoded in the nucleus and translated in the cytoplasm. Cells therefore rely on elaborate protein trafficking systems to ensure these proteins are distributed from the cytoplasm 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 understand the mechanism of protein targeting and import into chloroplasts. We are interested in this system as it serves as a model for intracellular protein trafficking and organelle biogenesis in all eukaryotes, and because plastids play a central role in plant growth and development.  Not only do chloroplasts house the reactions of photosynthesis, but plastids are also the sites of other essential biochemical pathways such as amino acid and lipid biosynthesis. Protein import into chloroplasts relies on translocon complexes located at the double membrane envelope that surrounds the organelle. The focus of my research program is to understand how the pecision of protein import into chloroplasts is achieved by these translocons. Knockout mutants of the model plant Arabidopsis thaliana lacking individual translocon components will be used to determine how pairs of translocon components work together to decode specific plastid proteins. This strategy will be coupled with established in vitro protein-protein interaction assays to determine which components associate with one another, and in so doing impart specificity to the protein recognition function of the translocon. A more thorough understanding of the mechanism of protein import into chloroplasts and how the process is regulated will contribute to our broader understanding of plant growth and development.