Molecular Mechanism of Protein Transport into Chloroplasts

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Many essential metabolic pathways in plant cells occur within the chloroplast. Although some of the proteins and enzymes required for these processes are synthesized within the chloroplast itself, the vast majority of these proteins are synthesized as precursors in the cytoplasm of plant cells and are subsequently transported into chloroplasts. Import of these proteins into chloroplasts is mediated by an import apparatus located on the chloroplast surface. The long-term goal of this project is to identify the proteins that constitute the import apparatus of the model plant Arabadopsis and to clarify the biochemical mechanisms by which individual proteins of the import apparatus contribute to the transport of precursor proteins into chloroplasts. This project uses a genetic approach to investigate the function of selected proteins that operate as the molecular motor of the import machinery, by providing the driving force for the transport process. Transgenic plants will be constructed in which the normal Arabadopsis protein has been either inactivated or replaced with an altered form of the protein. Cell biological and biochemical experiments will then be used to evaluate the effect of the gene alterations on the transport process. The transport process will be studied in plants expressing either one altered protein or multiple altered proteins. This strategy will elucidate the functions of individual proteins and also provide information about interactions between the various proteins. The new understanding of protein import derived from this project will be useful for efforts that involve the engineering of various chloroplast-specific metabolic pathways. For instance, novel enzymes that synthesize unique fatty acids could be targeted to chloroplasts to create plants with modified fatty acids that have improved nutritional or industrial value. Hence, this research will both advance our basic understanding of protein targeting to chloroplasts and have the practical impact by improving our ability to engineer and modify plants for a variety of uses.