Molecular Mechanisms of Endoplasmic Reticulum Formation in Plant Cells

植物被人类用来生产食物、衣服、建筑材料和药物。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，一直是生物技术提高食物、油和药物积累的目标，但ER在植物细胞中如何形成和重塑在很大程度上是未知的。作为相互连接的小管和片的细胞网络，ER的形状经历响应于发育线索的变化。通过我之前的NSERC发现赠款，我们证明了，根毛缺陷3（RHD 3），一种拟南芥atlastin GTd 3，通过介导不同ER小管的融合（Zhang et al 2013）参与细胞发育期间互连ER网络的产生和重塑（Chen et al 2011）。我们最近还表明，RHD 3与微管一起，在小ROP 2 GTdR的指导下，在拟南芥根毛尖端生长期间产生用于局部分泌的精细ER中起着至关重要的作用（Qi et al 2016）。rhd 3突变体表现出短而波浪状的根毛，使rhd 3成为进一步研究植物ER形成的调控和功能的理想遗传模型系统，特别是在根毛顶端生长期间。在这个建议中，我想利用体内成像，生物化学和遗传学方法开发的信息，进一步研究RHD 3如何与其他蛋白质一起形成ER，以及这些相互作用如何参与根毛的尖端生长。本研究的具体目的是：1）研究锌指基序蛋白LUNAPARK 2（LNP 2）对RHD 3活性的调节; 2）证明RHD 3介导的在局部根毛顶端生长中形成精细ER需要ARMADILLO-REPEAT KINESIN 1（ARK 1）的作用，ARK 1是一种微管加末端运动蛋白; 3）表征吲哚洛芬（一种抑制rhd 3的非甾体抗炎药）的分子作用;和4）克隆和鉴定RHD 3、REN 4和REN 10的抑制子RSU 1，两个rhd 3增强子，以进一步探索RHD 3如何与这些基因一起在内质网小管融合以及根毛的尖端生长中发挥作用。这些工作有望产生新的见解如何形成的管状ER网络。了解ER是如何在植物细胞中形成和重塑的，将有助于未来基于植物的材料生产的合理设计。此外，植物是固着生物，由不能移动的细胞组成。在普遍的环境条件下，植物细胞各自生长成特定的大小和形状，从而有助于生物体的整体形式和功能。这项拟议中的研究将揭示一些允许植物细胞做到这一点的机制。随着对植物细胞如何生长的理解的加深，我们很可能在不久的将来能够以更低的投入或在更贫瘠的土地上生产产品。

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.