Poster: Protein targeting & vesicular trafficking

Abs # 661: Plant-specific mitotic targeting of RanGAP requires a functional WPP domain

Presenter:	Jeong, Sun Yong , jeong.25@osu.edu
Authors	Jeong, Sun Yong  (A)   Rose, Annkatrin  (A)   Joseph, Jomon  (B)   Dasso, Mary  (B)   Iris, Meier  (A)
Affiliations:	(A): Department of Plant Biology and Plant Biotechnology Center, Ohio State University, Columbus, OH 43210 (B): Laboratory of Gene Regulation and Development, National Institutes of Health, Bethesda, MD 20892

In animals and yeast, the small GTPase Ran is involved in nucleocytoplasmic transport, spindle formation, and nuclear envelope formation. These functions are controlled by a RanGTPase-activating protein (RanGAP) and a guanine nucleotide exchange factor (RCC1). Vertebrate RanGAP1 is conjugated with the ubiquitin-like protein SUMO. SUMOylation of RanGAP1 is required for nuclear envelope-association in interphase and for spindle and centromere association in mitosis. Plant RanGAP lacks the SUMOylated C-terminal domain of vertebrate RanGAP, but contains instead a plant-specific N-terminal domain, called WPP domain, which is necessary and sufficient for targeting the protein to the nuclear rim. By examining the localization of Arabidopsis RanGAP1 during the cell cycle in stably transformed tobacco BY2 cells expressing AtRanGAP1-GFP, we found that AtRanGAP1 localizes to the nuclear rim during interphase and to the cell plate during cytokinesis. A WPP domain-GFP fusion behaves like full-length AtRanGAP1-GFP, while WPP-domain deletion abolishes all targeting, demonstrating that the WPP domain is necessary and sufficient for both targeting events. Point mutations in conserved residues of the WPP domain abolish targeting to the nuclear rim and the cell plate, suggesting that the same mechanism is involved in anchoring RanGAP1 in both locations. These results imply a novel function of AtRanGAP1 during cell cycle and suggest a role of the Ran cycle in controlling cell plate formation in plant cytokinesis.