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Plant and Cell Physiology Advance Access published online on October 17, 2005
Plant and Cell Physiology, doi:10.1093/pcp/pci215
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Plant and Cell Physiology 2005 © The Japanese Society of Plant Physiologists (JSPP); all rights reserved.
Received August 22, 2005
Accepted October 7, 2005

Regular Paper

OsGAP1 Functions As a Positive Regulator of OsRab11-Mediated TGN to PM or Vacuole Trafficking

Jae Bok Heo 1, Hee Sun Rho 2, Se Won Kim 1, Sung Min Hwang 1, Hyun Jin Kwon 1, Min Yeop Nahm 1, Woo Young Bang 1, and Jeong Dong Bahk 3*

1 Division of Applied Life Sciences, Graduate School of Gyeongsang National University, Jinju 660-701, Korea
2 Environmental Biotechnology National Core Research Center (EBNCRC), Gyeongsang National University, Jinju 660-701, Korea
3 Division of Applied Life Sciences, Graduate School of Gyeongsang National University, Jinju 660-701, Korea; Environmental Biotechnology National Core Research Center (EBNCRC), Gyeongsang National University, Jinju 660-701, Korea

* To whom correspondence should be addressed.
Jeong Dong Bahk, E-mail: jdbahk{at}gsnu.ac.kr


  Abstract

The Ypt/Rab family of small G-proteins is important in regulating vesicular transport. Rabs hydrolyze GTP very slowly on their own and require GTPase-activating proteins (GAPs). Here we report the identification and characterization of OsGAP1, a Rab-specific rice GAP. OsGAP1 strongly stimulated OsRab8a and OsRab11, which are homologues of the mammalian Rab8 and Rab11 proteins that are essential for Golgi to plasma membrane (PM) and trans-Golgi network (TGN) to PM trafficking, respectively. Substitution of two invariant arginines within the catalytic domain of OsGAP1 with alanines significantly inhibited its GAP activity. In vivo targeting experiments revealed that OsGAP1 localizes to the TGN or prevacuolar compartment (PVC). A yeast expression system demonstrated that wild-type OsGAP1 facilitates OsGDI3-catalyzed OsRab11 recycling at an early stage but the OsGAP1(R385A) and (R450A) mutants do not. Thus, GTP hydrolysis is essential for Rab recycling. Moreover, expression of the OsGAP1 mutants in Arabidopsis protoplasts inhibited the trafficking of some cargo proteins, including the PM-localizing H+-ATPase-GFP and Ca2+-ATPase8-GFP proteins and the central vacuole-localizing AALP-GFP protein. The OsGAP1 mutants caused these proteins to accumulate at the Golgi apparatus. Surprisingly, OsRab11 overproduction relieved the inhibitory effect of the OsGAP1 mutants on vesicular trafficking. OsRab8a had no such effect. Thus, the OsGAP1 mutants may inhibit TGN to PM or central vacuole trafficking because they induce the sequestration of endogenous Rab11. We propose that OsGAP1 facilitates vesicular trafficking from the TGN to the PM or central vacuole by both stimulating the GTPase activity of OsRab11 and by increasing the recycling of inactive OsRab11.

Keywords: vesicular trafficking; OsGAP1; OsRab11; trans-Golgi network; prevacuolar compartment.
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