Anchorage of Plant RanGAP to the Nuclear Envelope Involves Novel Nuclear-Pore-Associated Proteins

Abstract

The Ran GTPase controls multiple cellular processes including nucleocytoplasmic transport, spindle assembly, and nuclear envelope (NE) formation [1-4]. Its roles are accomplished by the asymmetric distribution of RanGTP and RanGDP enabled by the specific locations of the Ran GTPase-activating protein RanGAP and the nucleotide exchange factor RCC1 [5-8]. Mammalian RanGAP1 targeting to the NE and kinetochores requires interaction of its sumoylated C-terminal domain with the nucleoporin Nup358/RanBP2 [9-14]. In contrast, Arabidopsis RanGAP1 is associated with the NE and cell plate, mediated by an N-terminal, plant-specific WPP domain [15-18]. In the absence of RanBP2 in plants, the mechanism for spatially sequestering plant RanGAP is unknown. Here, Arabidopsis WPP-domain interacting proteins (WIPs) that interact with RanGAP1 in vivo and colocalize with RanGAP1 at the NE and cell plate were identified. Immunogold labeling indicates that WIP1 is associated with the outer NE. In a wip1-1/wip2-1/wip3-1 triple mutant, RanGAP1 is dislocated from the NE in undifferentiated root-tip cells, whereas NE targeting in differentiated root cells and targeting to the cell plate remain intact. We propose that WIPs are novel plant nucleoporins involved in RanGAP1 NE anchoring in specific cell types. Our data support a separate evolution of RanGAP targeting mechanisms in different kingdoms.

RanGAP1 is a continuous marker of the Arabidopsis cell division plane

“…However, WIPs appear dispensable for RanGAP1 phragmoplast midline/cell plate targeting during cytokinesis (18). Similarly, the mitotic targeting of RanGAP1 to the PPB, kinetochore, or CDS does not depend on WIPs, supporting the notion that different mechanisms are involved in targeting plant RanGAP at different cell cycle stages (Fig.…”

“…Arabidopsis RanGAP1 concentration at the nuclear envelope in nondifferentiated root tip cells is dependent on a group of nuclear pore-associated proteins (WIPs) (18). However, WIPs appear dispensable for RanGAP1 phragmoplast midline/cell plate targeting during cytokinesis (18).…”

Dynamics of the Plant Nuclear Envelope and Nuclear Pore

“…There are now a significant number of proteins available to serve as markers for NE dynamics in plants: NMCP1/2 (LINC1/2), SUN1/2, WPP DOMAIN-INTERACTING PROTEIN1 (WIP1)/2/3, WPP DOMAIN-INTERACTING TAIL-ANCHORED PROTEIN1 (WIT1)/2, and Nuclear Pore Anchor (NUA; Dittmer et al, 2007;Jacob et al, 2007;Xu et al, 2007aXu et al, , 2007bZhao et al, 2008;Graumann et al, 2010;Fig. 1A).…”

“…For instance, Arabidopsis ONM proteins, WIP1, WIP2, WIT1, and WIT2, are redistributed to the cell plate during cytokinesis (Patel et al, 2004;Xu et al, 2007a;Zhao et al, 2008;Fig. 2).…”

Nuclear translocation of RanGAP1 coincides with virtual nuclear envelope breakdown in fission yeast meiosis

“…[8][9][10] In the plant Arabidopsis thaliana, RanGAP1 lacks the SUMO1 attachment domain and instead contains a plant-specific WPP domain which interacts with NE-associated WIP proteins. 11,12 These domains result in concentrated localization of RanGAP1 at the NE. The majority of closed mitosis organisms also lack a SUMO1 attachment domain in their RanGAP1 proteins, but unlike plant RanGAP1 their RanGAP1 proteins have no alternative domains for NE attachment and do not show significant localization at the NE.…”