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Title: ENDOPLASMIC RETICULUM TO VACUOLE TRAFFICKING OF ENDOPLASMIC RETICULUM BODIES PROVIDES AN ALTERNATE PATHWAY FOR PROTEIN TRANSFER TO THE VACUOLE

Author
item Herman, Eliot
item Schmidt, Monica

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2004
Publication Date: 11/1/2004
Citation: Herman, E.M., Schmidt, M.A. 2004. Endoplasmic reticulum to vacuole trafficking of endoplasmic reticulum bodies provides an alternate pathway for protein transfer to the vacuole. Plant Physiology. 136:3440-3446.

Interpretive Summary: In order to mediate developmental changes, plants have evolved a subcelluar compartment called endoplasmic reticulum (ER) ER-bodies. These ER-bodies provide a mechanism to assemble, transport and store proteins, oil and rubber in subcellular compartments derived directly from the cell's site of synthesis, the endoplasmic reticulum. The recognition that plants produce ER-bodies is recent and appears to be one of the fundamental differences between plants and other eukaryotes such as animals and fungi. As knowledge of the ER-bodies has increased this has left a knowledge gap as to why plants have evolved such a distinct mechanism. In this manuscript a model is proposed that ER-bodies provide a mechanism to produce and transport aggregates of protein, oil or rubber that would be too large to transport through normal cellular trafficking common to animals, fungi and plants. Understanding this process is potentially useful as a means to induce plants to store the products of genetic manipulation and the model presented. The information presented is primarily directed at academic investigators but is also useful to industry scientists interested in increasing the accumulation of the products of genetic modification.

Technical Abstract: One of the emerging differences between plants and other eukaryotes is the accretion or aggregation of substances in the endoplasmic reticulum (ER) to form ER bodies. These ER bodies can contain accumulations of triglyceride oils, rubber, storage proteins and precursors of enzymes. Why plants produce ER bodies with this diverse array of substances and how this difference is a characteristic of plants remains a subject of discussion. In this paper a new model is presented that plants have evolved ER bodies as a means to bypass Golgi-mediated progression through the endomembrane system. This strategy provides a means by which protein and rubber aggregates too large to be packaged for transport from the ER and through the Golgi can be packaged by an alternate pathway into an organelle. By sequestering ER-bodies in the vacuiole via autophagy this provides a means to deliver large aggregates to the vacuole where its delivery results modifying the vacuole's composition and the function of the plant cells. Plant cells often undergo one or more remodeling events during their life cycle. The formation of ER-bodies and the delivery of the ER-body contents to the vacuole is one of the key events in the ontogeny of storage cells and senescence of plants.