The Formation of Endoplasmic Reticulum and the Shape of Plants

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The endoplasmic reticulum (ER) is a polygonal network of interconnected tubules stretching inside cells. The ER is the site where proteins and lipids are made. The long term objective of my research is to understand how the ER is formed and how proteins and lipids are made and transported inside plant cells as cell morphology changes during plant growth. We recently show that a plant protein called RHD3 plays an important role in the generation of interconnected polygonal ER tubules (Chen et al., 2011. J. Cell Sci.124:2241). In this proposal, we will further investigate how RHD3, together with other proteins, controls the formation of interconnected ER network. We will use a living cell imaging technology to 1) quantify the cellular action of RHD3 on ER tubules; using a combined method of genetics, biochemistry and living cell imaging to 2) investigate the regulation of RHD3 by another protein called TIP1 and 3) to study the role of the RHD3 interaction with a protein called PIS2 in the generation of interconnected ER tubules. In Arabidopsis, mutations in RHD3 affect the direction of cell growth, resulting in abnormally-shaped cells in both roots and shoots. Plant cells are surrounded by an extracellular matrix called cell wall, composed of mainly cellulosic microfibrils. A linear distribution of cellulosic microfibrils perpendicular to the direction of cell growth is important for plant cells to grow in right direction. Because the rhd3 mutant is defective in the accumulation of cellulose, we will 4) investigate how cellulose and other cell wall materials are transported and positioned in the rhd3 mutant. Plants are used by the humans to produce food, clothes, wood and medicines. The ER of plant cells has been a target of biotechnology for improved accumulation of food, oils and pharmaceuticals. Understanding how the ER is formed will help rational design of plant-based production of materials. Secondly, there has been an increasing demand of using plant cell walls as new biofuels, but how plant cells assemble and organize the diverse components of the wall on the outside of the cell is not well understood. The proposed research will shed lights on how cell wall materials are secreted and positioned properly in plant cells.