Chloroplast Protein Transport in the Moss Physcomitrella Patens

University Of California-Davis, Davis CA

Investigators

Abstract

Chloroplasts are the subcellular compartment responsible for photosynthesis, the process that uses the energy of sunlight to convert carbon dioxide and water to sugar and oxygen. Photosynthesis is accomplished by complexes of proteins within the chloroplast, which are encoded by both nuclear genes and chloroplast genes. Approximately 90% of the chloroplast proteins are actually synthesized outside the chloroplast and must be imported from the cytoplasm prior to their assembly into the photosynthetic apparatus. Most of these proteins enter the chloroplast through a general translocation machinery located in the chloroplast envelope. While the identities of some of these translocation proteins are known, their specific roles are only now being elucidated. This application proposes to examine the function of two proteins thought to play a role in envelope protein translocation, Toc64 and stromal Hsp70. The experiments will be performed in the moss Physcomitrella patens, a model plant in which introduced foreign genes readily recombine in the nucleus with the homologous endogenous genes, allowing for targeted gene knockout and replacement. This process of homologous recombination will be used to the eliminate Toc64 and Hsp70 genes, and the mutant plants will be examined for defects chloroplast maturation and development. Chloroplasts will also be isolated from the mutant plants and used in biochemical experiments designed to identify defects in the chloroplast import machinery. Efforts to selectively improve crop traits will necessarily include targeting proteins to the chloroplasts, where much of the metabolic activity of a plant cell occurs. Thus a full understanding of the mechanisms through which chloroplasts import proteins, the subject of the proposed research, is crucial for realizing the full potential of plant genetic engineering on improving human health and nutrition. In addition, this research will result in the training of numerous graduate and undergraduate students, and postdoctoral scientists.