Functional analyses of the plant-specific C-terminal region of VPS9a: the activating factor for RAB5 in Arabidopsis thaliana
- 689 Downloads
Recent studies demonstrated that endosomal transport played important roles in various plant functions. The RAB GTPase regulates the tethering and fusion steps of vesicle trafficking to target membranes in each trafficking pathway by acting as a molecular switch. RAB GTPase activation is catalyzed by specific guanine nucleotide exchange factors (GEFs) that promote the exchange of GDP on the RAB GTPase with GTP. RAB5 is a key regulator of endosomal trafficking and is uniquely diversified in plants; the plant-unique RAB5 group ARA6 was acquired in addition to conventional RAB5 during evolution. In Arabidopsis thaliana, conventional RAB5, ARA7 and RHA1 regulate the endosomal/vacuolar trafficking pathways, whereas ARA6 acts in the pathway from the endosome to the plasma membrane. Despite their distinct functions, all RAB5 members are activated by the common GEF VACUOLAR PROTEIN SORTING 9a (VPS9a). VPS9a consists of an N-terminal conserved domain and C-terminal region (CTR) with no similarity to known functional domains. In this study, we investigated the function of the CTR by generating truncated versions of VPS9a and found that it was specifically responsible for ARA6 regulation; moreover, the CTR was required for the oligomerization and correct localization of VPS9a. The oligomerization of VPS9a was mediated by a distinctive region consisting of 36 amino acids in the CTR that was conserved in plant RAB5 GEFs. Thus the VPS9a CTR plays an important role in the regulation of the two RAB5 groups in plants.
KeywordsArabidopsis thaliana Endosome Guanine nucleotide exchange factor RAB5 VPS9a
We thank Dr. T. Nakagawa (Shimane University), Dr. S. Shimizu (Tokyo Medical and Dental University) and Dr. T. Demura (NAIST) for sharing materials and Dr. K. Ebine and Dr. E. Ito (The University of Tokyo) for critical reading of the manuscript. This study was supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (A.N. and T.U.), JST, PRESTO (T.U.), and a Grant-in-Aid for JSPS Fellows (M.S.).
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
- Bravo-Sagua R, Torrealba N, Paredes F, Morales PE, Pennanen C, López-Crisosto C, Troncoso R, Criollo A, Chiong M, Hill JA, Simmen T, Quest AF, Lavandero S (2014) Organelle communication: signaling crossroads between homeostasis and disease. Int J Biochem Cell Biol 50:55–59PubMedCrossRefGoogle Scholar
- Fukuda M, Wen L, Satoh-Cruz M, Kawagoe Y, Nagamura Y, Okita TW, Washida H, Sugino A, Ishino Y, Ishino S, Ogawa M, Sunada M, Ueda T, Kumamaru T (2013) A guanine nucleotide exchange factor for Rab5 proteins is essential for intracellular transport of the proglutelin from the Golgi apparatus to the protein storage vacuole in rice endosperm. Plant Physiol 162:663–674PubMedPubMedCentralCrossRefGoogle Scholar
- Haas TJ, Sliwinski MK, Martínez DE, Preuss M, Ebine K, Ueda T, Nielsen E, Odorizzi G, Otegui MS (2007) The Arabidopsis AAA ATPase SKD1 is involved in multivesicular endosome function and interacts with its positive regulator LYST-INTERACTING PROTEIN5. Plant Cell 19:1295–1312PubMedPubMedCentralCrossRefGoogle Scholar
- Kunita R, Otomo A, Mizumura H, Suzuki K, Showguchi-Miyata J, Yanagisawa Y, Hadano S, Ikeda JE (2004) Homo-oligomerization of ALS2 through its unique carboxyl-terminal regions is essential for the ALS2-associated Rab5 guanine nucleotide exchange activity and its regulatory function on endosome trafficking. J Biol Chem 279:38626–38635PubMedCrossRefGoogle Scholar
- Ren M, Xu G, Zeng J, De Lemos-Chiarandini C, Adesnik M, Sabatini DD (1998) Hydrolysis of GTP on rab11 is required for the direct delivery of transferrin from the pericentriolar recycling compartment to the cell surface but not from sorting endosomes. Proc Natl Acad Sci USA 95:6187–6192PubMedPubMedCentralCrossRefGoogle Scholar
- Zhu H, Liang Z, Li G (2009) Rabex-5 is a Rab22 effector and mediates a Rab22–Rab5 signaling cascade in endocytosis. Mol Biol Cell 20:4072–4729Google Scholar