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)作为蛋白质和脂类的合成、运输和积累的场所，一直是 生物技术，以改善粮食、油类和 药物，但内质网是如何在植物细胞中形成和重塑的，在很大程度上还不清楚。作为相互连接的小管和薄片的细胞网络，内质网的形状随着发育线索的变化而发生变化。通过我之前的NSERC发现拨款，我们证明了根毛缺陷3(RHD3)，一个拟南芥atlastin GTP酶，通过调节不同ER管的融合参与了细胞发育过程中相互连接的ER网络的生成和重塑(Chen等人，2011)(Zhang等人，2013)。我们最近还发现，RHD3与微管一起，在小ROP2 GTP酶的指导下，在拟南芥根毛顶端生长过程中为局部分泌产生精细内质网起着至关重要的作用(齐等人2016)。Rhd3突变体的根毛短而卷曲，使其成为理想的根毛。 用于进一步研究调控和功能的遗传模型系统 内质网在植物中的形成，特别是在根尖生长期间 头发。在这份提案中，我希望以我使用体内成像、生化和遗传学方法开发的信息为基础，进一步研究RHD3如何与其他蛋白质一起在内质网的形成中发挥作用，以及这些相互作用如何参与根毛的顶端生长。该方案的具体目的是：1)研究锌指基序蛋白LUNAPARK2(LNP2)对RHD3活性的调节；2)证明RHD3介导的细小ER的形成需要微管和末端运动蛋白Ark1(Ark1)的作用；3)研究抑制RHd3的非类固醇抗炎药吲哚洛芬的分子作用；4)克隆和鉴定RHD3的抑制子rsu1和两个Rhd3的增强子ren4和ren10，以进一步探讨RHD3与这些基因在内质网小管融合和根毛顶端生长中的作用。这些工作有望对管状ER网络的形成产生新的见解。了解ER是如何形成和重构的 植物细胞将有助于合理设计以植物为基础的生产 未来的材料。此外，植物是固着的有机体，由不能移动的细胞组成。在普遍的环境条件下，植物细胞每一个都生长以采用特定的大小和形状，这有助于有机体的整体形式和功能。这项拟议中的研究将阐明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了解的加深，我们很可能在不久的将来能够以更低的投入或在更边际的土地上生产产品。

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.