RanGAP, the GTPase-Activating Protein (GAP) of the small GTPase Ran, is vital for nucleocytoplasmic trafficking of protein cargo in yeast and animals via the Ran cycle, and mitotic cell division. Arabidopsis thaliana contains two RanGAP paralogs, namely RanGAP1 and RanGAP2. Despite the functional information of RanGAP revealed by extensive studies in yeast and animals, and its high degree of conservation in structure, GAP activity and sub-cellular localization in plants, involvement of RanGAP in plant development is poorly understood. Studies in plants would provide clues on the evolutionary conservation and digression of RanGAP’s roles among eukaryotes, and would also enable insight into its effects on a whole-organism level in a system that undergoes indeterminate development. Here, I have used a genetic approach to generate a series of T-DNA insertion lines in Arabidopsis thaliana that contain decreasing RanGAP levels and increasing severity in vegetative and reproductive phenotypes. The mutants provide valuable experimental material to dissect the functions of plant RanGAP. I have analyzed several of these phenotypes in detail and revealed the importance of Arabidopsis RanGAP in plant genesis, survival and development. The implications of mitotic involvement of RanGAP underlying these phenotypes points to a general conservation of RanGAP functionality in planta, in common with yeast and animals.
In an independent effort, molecular mechanisms underlying the functions of Tandem Zinc Finger 1 of Arabidopsis thaliana (AtTZF1) were investigated. AtTZF1 is a plant-unique CCCH-type tandem zinc finger (TZF) protein implicated in drought and cold stress tolerance via regulation of gene expression. Studies with the most well studied human TZF; hTTP and AtTZF1 collectively suggest that the functions of AtTZF1 may be mediated by the dynamics in the assembly of stress responsive cytoplasmic mRNA-protein complexes; stress granules (SGs) and P-bodies (PBs), phosphorylation of AtTZF1 by the Mitogen-Activated Protein Kinase (MAPK) pathway and positive regulation of ABA-mediated gene expression in planta. Understanding the mode of function of AtTZF1 particularly in stress tolerance could be useful in developing agronomically important crops. To investigate the molecular mechanisms of AtTZF1 functions that currently remain elusive, assays on protein-protein interaction and AtTZF1 phosphorylation were conducted. Since the assays based on putative candidates were unable to reveal authentic molecular partners for AtTZF1, alternative approches may be used for future investigations.