Function of the Nuclear Ran/RCCI Regulatory System in Plants

9506985 Gruissem细胞通过控制它们进入细胞周期的进程来调节它们的生长，但这些控制的分子机制还不是很清楚。已有研究表明，核Ras样GTP结合蛋白RAN及其核苷酸交换因子RCC1形成一个复合体，对许多核功能至关重要，包括进入和进行DNA复制，以及进入细胞分裂。RAN或RCC1的突变在动物和酵母细胞中具有复杂的表型，并影响许多过程，包括DNA合成和基因表达，经常导致细胞死亡。本课题旨在研究Ran和RCC1在植物细胞分裂和有性生殖中的作用。对多细胞系统中的RAN/RCC1调节复合体的拟议研究将揭示这些保守蛋白质的新功能，但目前尚不清楚。初步数据表明，植物RAN是一种高度保守的核蛋白，可以抑制酵母细胞周期的分裂突变。RAN是由番茄中的一个基因家族编码的，这些基因的成员是差异表达的。通过诱导表达突变型RAN蛋白的转基因番茄植株，研究RAN和RCC1在番茄中的功能。这是一个新的和强大的工具来研究这些蛋白质在发育中的作用。此外，这些蛋白质在细胞分裂和有性繁殖过程中的亚细胞分布和功能还不清楚。植物细胞为这种功能和定位研究提供了一个有用的遗传系统。综上所述，这些实验为了解RAN/RCC1调控复合体在信号转导网络中的功能奠定了重要的基础，该信号转导网络调控细胞生长和细胞分裂的整合。在进入细胞周期的任何阶段，都有复杂而多样的功能必须协调。导致有丝分裂启动的阶段，即细胞周期的M期，需要并在某种程度上可能受到多种活动的驱动，其中一些涉及RAN基因产物及其相关的RCC1基因产物。然而，迄今为止对这些基因的研究主要是在酵母和哺乳动物系统中完成的。这项工作汇集了以前在酵母和哺乳动物细胞组织培养方面所做的有启发性的工作，并提供了一种通过在番茄和拟南芥植物中使用转基因技术来确定该基因复合体最终功能的方法。研究已经表明，植物中的Ran/RCC1基因与酵母和哺乳动物中的基因非常相似。这项工作还表明，植物基因可以在功能上取代酵母中的非功能基因。结束对植物的这些研究利用了减数分裂中已知的多个植物突变，减数分裂是产生有性配子的“减少”分裂。有丝分裂和减数分裂早期阶段之间的共性表明，通过利用这一植物生物学领域的高级知识，这些蛋白质的确切作用可能被揭示出来。将这项工作扩展到植物也利用了成熟、分化的高等植物中“自然”发生的细胞周期停滞点和活动。RAN/RCC1调控复合体在参与植物正常发育的信号转导网络中的作用的发现，将有助于我们更深入地理解这些非常基本的、常见的信号机制在植物、动物和真菌生长过程中是如何协调的。***

9506985 Gruissem Cells regulate their growth by controlling their progression into the cell cycle, but the molecular mechanisms for these controls are not well understood. It has been shown that the nuclear Ras-like GTP-binding protein Ran and its nucleotide exchange factor RCC1 form a complex that is critical for a number of nuclear functions, including entry into and progression of DNA replication, and entry into cell division. Mutations in either Ran or RCC1 have complex phenotypes in animal and yeast cells and affect many processes, including DNA synthesis and gene expression, often resulting in cell death. This project is an investigation of the functions of Ran and RCC1 in plant cell division and sexual reproduction. The proposed studies of the Ran/RCC1 regulatory complex in a multicellular system that is amenable to in vivo manipulations should reveal novel and as yet poorly understood functions for these conserved proteins. Preliminary data indicate that plant Ran is a highly conserved nuclear protein which can suppress a fission yeast cell cycle mutation. Ran is encoded by a family of genes in tomato whose members are differentially expressed. The function of Ran and RCC1 in tomato plants will be investigated using transgenic tomato plants expressing mutant Ran proteins in an inducible fashion. This is a novel and powerful tool to investigate the role of these proteins in development. In addition, the subcellular distribution and function of the proteins during cell division and sexual reproduction are not understood. Plant cells present a useful genetic system for such functional and localization studies. Together, these experiments establish an important basis for studies to understand the function of the Ran/RCC1 regulatory complex in a signal transduction network that regulates the integration of cell growth and cell division %%% During entry into any phase of the cell cycle, there are complex and diverse functions which must be coor dinated. The phase which leads to initiation of mitosis, the M phase of the cell cyle, requires, and to some degree may be driven by, multiple activities, some of which involve the Ran gene product and its associated RCC1 gene product. However, the work to date on these genes has been done primarily in yeast and mammalian systems. This work pulls together the suggestive previous work done in yeast and mammalian cell tissue culture and provides a means to determine definitive functions of this gene complex through the use of transgenic technologies in tomato and Arabidopsis plants. Work has already shown that the genes for Ran/RCC1 in plants are very similar to those found in yeast and mammals. The work also shows that the plant genes can functionally replace non-functional genes in yeast. Ending these studies to plants takes advantage of the multiple known plant mutations in meiosis, the "reduction" division which gives rise to sexual gametes. The commonality between the early phases of mitosis and meiosis would indicate that the definitive role for these proteins might be uncovered by exploiting advanced knowledge in this area of plant biology. Extending the work to plants also takes advantage of the "naturally" occuring cell cycle arrest points and activity in a mature, differentiated higher plant. Discovery of the role of the Ran/RCC1 regulatory complex in the signal transduction network involved in the normal development of plants should provide a deeper of understanding of how these very basic, common signaling mechanisms are coordinated during plant, animal and fungal growth. ***