Elucidating the biogenesis of peroxisomes in plants: Formation of peroxisomes at the ER and membrane protein trafficking, and peroxisome-organelle interactions

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A hallmark of eukaryotic cells is the compartmentalization or "division of labor" of distinct metabolic pathways into separate subcellular organelles, a process that is mediated by the proper intracellular trafficking of each organelle's protein constituents. Research described in this proposal is a continuum of our overarching goal of understanding the biology of plant peroxisomes - organelles that participate in a vast array of metabolic and physiological functions in plants. Indeed, recent studies have revealed new and unexpected roles for plant peroxisomes, indicating that this organelle is a key target for future bioengineering or molecular breeding strategies aimed at modifying plant metabolism, energy-dense biomass production, stress tolerance and pathogen defense responses. *** Plant peroxisomes are remarkably dynamic in terms of their biogenesis, i.e., how they are initially formed and maintained in the cell, how they interact with other organelles, and ultimately how they are turned over. The emphasis of the proposed research is aimed at elucidating the complex molecular mechanisms that underlie these processes. Specifically, our objectives are to decipher the role of the endoplasmic reticulum (ER) in the formation of new peroxisomes and/or the maintenance of pre-existing peroxisomes, and how this process compares to the formation of new organelles by peroxisomal fission. We also plan to elucidate the specific region(s) of the ER at which peroxisomes are thought to originate, as well as the molecular targeting signals that direct membrane proteins to peroxisomes via different pathways, and to potentially different subpopulations of peroxisomes. Other proposed research involves characterization of the physical associations between peroxisomes and the ER, as well as with lipid droplets, which are subcellular organelles that store lipids in plant cells. These interactions ensure the metabolic cooperation and communication between peroxisomes and other organelles and appear to be mediated by distinct proteins that serve as membrane tethers'. *** Overall, the proposed research will utilize multidisciplinary, but complementary molecular, biochemical and cell biology-based approaches to discover new and important principals of peroxisome biology in plants and, in doing so, provide basic knowledge that will be instrumental for the future design of crops that produce important nutritional and industrial bioproducts. This research will also provide trainees with opportunities to engage in cutting-edge scientific endeavours, with an explicit emphasis on problem solving and collaboration building. These activities, combined with guidance and encouragement, will continue to lead to high-impact publications and the development of imaginative, independent young scientists who will be well prepared for careers in academia, government and/or industry.