Localization of translation and non-translated mRNAs; functions, mechanisms and novel compartments

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Plants and algae obtain energy for growth and reproduction from light using a process called photosynthesis. Photosynthesis occurs in subcellular organelles called chloroplasts. Our previous research revealed that chloroplasts contain compartments for the synthesis of proteins and RNA quality control. We are analyzing these compartments as an avenue to understand biogenesis and quality control in this organelle and, we hope, reveal general principles of Cell Biology. One goal of this research program is to understand how the membranes that make up thylakoid vesicles within chloroplasts are made. Thylakoid vesicles carry out the light-driven reactions of photosynthesis. We have identified a special region of the membranous envelope that encloses the chloroplast where proteins and chlorophyll of the thylakoids are generated. We show for the first time that the ribosomes of the cell's cytoplasm are synthesizing proteins in direct contact with the chloroplast. This has been show for most other organelles, but not for chloroplasts. Characterization of the composition of this novel biogenic domain of the chloroplast envelope will lead to new insights regarding the long-standing mystery regarding the developmental origins of thylakoid membranes and how they arise from the chloroplast envelope. Another goal is to characterize a compartment within the chloroplast that handles quality control of RNA. RNA is an important molecule in the transfer of genetic information from the gene to generate functional proteins. Chloroplasts have their own genome and gene expression system because they evolved from a free-living photosynthetic bacterium which took up residence in the primordial plant cell some 1-2 billion year ago. Since, chloroplasts have retained a downsized genome and gene expression system, including RNA. We identified and study structures are called "chloroplast stress granules" which handle RNA that has just left the protein synthesis machinery and is not being translated. These chloroplast stress granules are similar to stress granules found in all eukaryotic cells examined and even in bacteria called stress granules. We will characterize chloroplast stress granules to learn about how this organelle handles RNA quality control and, we hope, provide general insights into stress granule functions in all organisms. In summary, the results will be relevant to the development of biotechnologies for Canadian industries because algae are used in the food industry and as biosensors for environmental pollutants for decades. Algae are being engineered to efficiently produce high-value molecules at industrial scales; e.g. pharmaceuticals, vaccines, and food supplements. Realization of this potential will benefit from our research results regarding how proteins are synthesized in chloroplasts. The results will also contribute to the basic knowledge that will be required for the biotechnological improvement of crop plants in agriculture.