Molecular Mechanisms of Endoplasmic Reticulum Formation in Plant Cells

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Plants are used by the humans to produce food, clothing, building*materials and medicines. The endoplasmic reticulum (ER) of plant cells, as the site for synthesis, transport and accumulation of proteins and lipids, has been a target of*biotechnology for improved accumulation of food, oils and*pharmaceuticals, but how the ER is formed and remodeled in plant cells is largely unknown. As a cellular network of interconnected tubules and sheets, the shape of the ER undergoes changes in response to developmental cues. With my previous NSERC discovery grants, we demonstrated that, ROOT HAIR DEFECTIVE 3 (RHD3), an Arabidopsis atlastin GTPase, is involved in the generation and re-shaping of the interconnected ER network during cell development (Chen et al 2011) by mediating the fusion of different ER tubules (Zhang et al 2013). We recently also show that, RHD3, together with microtubules, under the guidance of small ROP2 GTPase, plays an essential role in the generation of a fine ER for localized secretion during tip growth of Arabidopsis root hairs (Qi et al 2016). The rhd3 mutant exhibits short and wavy root hairs, making rhd3 an ideal*genetic model system for further studying the regulation and function*of ER formation in plants, especially during tip growth of root*hairs. In this proposal, I like to build on the information I have developed using in vivo imaging, biochemical and genetic methods to further study how RHD3 works together with other proteins in the formation of the ER and how these interactions participate in tip growth of root hairs. The specific objectives of this proposal are: 1) to investigate the regulation of RHD3 activity by LUNAPARK2 (LNP2), a zinc finger motif protein; 2) to demonstrate that RHD3-mediated formation of fine ER in localized tip growth of root hairs requires action of ARMADILLO-REPEAT KINESIN1 (ARK1), a microtubule plus end motor protein; 3) to characterize the molecular action of Indoprofen, a non-steroidal anti-inflammatory drug that suppresses rhd3; and 4) to clone and characterize rsu1, a suppressor of rhd3 and ren4 and ren10, two rhd3 enhancers to further explore how RHD3 may work with these genes in the fusion of ER tubules as well as in the tip growth of root hairs. These works are expected to yield new insights into how the tubular ER network is formed. Understanding how the ER is formed and remodeled in*plant cells will help rational design of plant-based production of*materials in the future. Furthermore, plants are sessile organisms, composed of cells that cannot move. In prevailing environmental conditions, plant cells each grow to adopt a specific size and shape that contribute to the overall form and function of the organism. The proposed research will shed lights on some of the mechanisms that allow plant cells to do this. With increased understanding of how plant cells grow, we are likely in the near future to be capable of producing products with lower inputs or on more marginal land.