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Plant Cell Advance Online Publication
Published on April 3, 2003; 10.1105/tpc.009779

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Received December 9, 2002
Accepted February 27, 2003

Rha1, an Arabidopsis Rab5 Homolog, Plays a Critical Role in the Vacuolar Trafficking of Soluble Cargo Proteins

Eun Ju Sohn 1, Eol Sun Kim 2, Min Zhao 3, Soo Jin Kim 2, Hyeran Kim 4, Yong-Woo Kim 4, Yong Jik Lee 4, Stefan Hillmer 5, Uik Sohn 6, Liwen Jiang 3, and Inhwan Hwang 7*

1 Center for Plant Intracellular Trafficking, Pohang University of Science and Technology, Pohang 790-784, Korea; Department of Genetic Engineering, Kyungpook National University, Daegu 702-701, Korea
2 Center for Plant Intracellular Trafficking, Pohang University of Science and Technology, Pohang 790-784, Korea
3 Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
4 Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea
5 Heidelberg Institute for Plant Sciences, University of Heidelberg, Heidelberg, Germany
6 Department of Genetic Engineering, Kyungpook National University, Daegu 702-701, Korea
7 Center for Plant Intracellular Trafficking, Pohang University of Science and Technology, Pohang 790-784, Korea; Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang 790-784, Korea

* To whom correspondence should be addressed. E-mail: ihhwang{at}postech.ac.kr.

Rab proteins are members of the Ras superfamily of small GTP binding proteins and play important roles in various intracellular trafficking steps. We investigated the role of Rha1, an Arabidopsis Rab5 homolog, in intracellular trafficking in Arabidopsis protoplasts. In the presence of a dominant-negative mutant of Rha1, soluble vacuolar cargo proteins such as sporamin:green fluorescent protein (Spo:GFP) and Arabidopsis aleurain like protein:GFP are not delivered to the central vacuole; instead, they accumulate as a diffuse or punctate staining pattern within the cell. Spo:GFP at the punctate stains observed in the presence of hemagglutinin:Rha1[S24N] is colocalized with endogenous vacuolar sorting receptor (VSRAt-1), which is known to localize primarily to the prevacuolar compartment, whereas Spo:GFP in the diffuse pattern is associated with tonoplasts. Furthermore, expression of Rha1[S24N] causes the secretion of a portion of the vacuolar proteins into medium. However, the inhibitory effect of Rha1[S24N] on vacuolar trafficking is relieved partially by coexpressed wild-type Rha1. Based on these results, we propose that Rha1 plays a critical role in the trafficking of soluble cargoes from the prevacuolar compartment to the central vacuole.






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