Molecular Mechanisms of Endoplasmic Reticulum Formation in Plant Cells

植物被人类用来生产食物、衣服、建筑材料和药品。植物细胞的内质网（ER）作为蛋白质和脂质合成、运输和积累的场所，一直是生物技术用于改善食物、油脂和药物积累的目标，但内质网在植物细胞中的形成和重塑在很大程度上是未知的。作为一个相互连接的小管和片的细胞网络，内质网的形状会随着发育的线索而发生变化。在我之前的NSERC发现资助下，我们证明了拟南芥的一种atlasatin GTPase - ROOT HAIR DEFECTIVE 3 （RHD3）通过介导不同内质网小管的融合参与细胞发育过程中内质网互联网络的生成和重塑（Chen et al . 2011） （Zhang et al . 2013）。我们最近也发现，在小ROP2 GTPase的引导下，RHD3与微管一起在拟南芥根毛生长过程中产生精细内质网，用于局部分泌中起着至关重要的作用（Qi et al 2016）。rhd3突变体的根毛较短，呈波浪状，是进一步研究植物内质网形成的调控和功能的理想遗传模型系统，特别是根毛尖端生长的内质网形成。在这个提案中，我想利用我利用体内成像、生化和遗传方法开发的信息，进一步研究RHD3如何与其他蛋白质一起形成内质网，以及这些相互作用如何参与根毛的尖端生长。本研究的具体目标是：1)研究锌指基序蛋白LUNAPARK2 （LNP2）对RHD3活性的调控；2)证明rhd3介导的根毛局部尖端生长中细小内质网的形成需要armadlo - repeat KINESIN1 （ARK1）的作用，ARK1是一种微管加末端运动蛋白；3)表征吲哚洛芬（一种抑制rhd3的非甾体抗炎药）的分子作用；4)克隆并鉴定rhd3抑制基因rsu1和rhd3增强基因ren4和ren10，进一步探讨rhd3如何在内质网小管融合和根毛尖端生长中与这些基因协同作用。这些工作有望对管状内质网如何形成产生新的见解。了解内质网是如何在植物细胞中形成和重塑的，将有助于未来合理设计基于植物的材料生产。此外，植物是由不能移动的细胞组成的无根生物。在普遍的环境条件下，植物细胞的每个细胞都生长成特定的大小和形状，这对生物体的整体形态和功能都有贡献。这项拟议的研究将揭示一些允许植物细胞这样做的机制。随着对植物细胞如何生长的了解的增加，我们很可能在不久的将来能够以更低的投入或更贫瘠的土地生产产品。

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.