Function of the Nuclear Ran/RCCI Regulatory System in Plants

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. ***

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. ***