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First published online 10 November 2009
doi: 10.1242/jcs.053488

Journal of Cell Science 122, 4383-4392 (2009)
Published by The Company of Biologists 2009
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Research Article

Arabidopsis Rab-E GTPases exhibit a novel interaction with a plasma-membrane phosphatidylinositol-4-phosphate 5-kinase

Luísa Camacho1,2,3, Andrei P. Smertenko2, José Pérez-Gómez1, Patrick J. Hussey2 and Ian Moore1,*

1 Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
2 The Integrative Cell Biology Laboratory, School of Biological and Biomedical Sciences, University of Durham, Durham, DH1 3LE, UK
3 Universidade de Lisboa, Faculdade de Ciências de Lisboa, ICAT, 1749-016 Lisboa, Portugal

* Author for correspondence (ian.moore{at}plants.ox.ac.uk)

Accepted 23 September 2009

Rab GTPases of the Arabidopsis Rab-E subclass are related to mammalian Rab8 and are implicated in membrane trafficking from the Golgi to the plasma membrane. Using a yeast two-hybrid assay, Arabidopsis phosphatidylinositol-4-phosphate 5-kinase 2 (PtdIns(4)P 5-kinase 2; also known as PIP5K2), was shown to interact with all five members of the Rab-E subclass but not with other Rab subclasses residing at the Golgi or trans-Golgi network. Interactions in yeast and in vitro were strongest with RAB-E1d[Q74L] and weakest with the RAB-E1d[S29N] suggesting that PIP5K2 interacts with the GTP-bound form. PIP5K2 exhibited kinase activity towards phosphatidylinositol phosphates with a free 5-hydroxyl group, consistent with PtdIns(4)P 5-kinase activity and this activity was stimulated by Rab binding. Rab-E proteins interacted with PIP5K2 via its membrane occupancy and recognition nexus (MORN) domain which is missing from animal and fungal PtdIns(4)P 5-kinases. In plant cells, GFP:PIP5K2 accumulated at the plasma membrane and caused YFP:RAB-E1d to relocate there from its usual position at the Golgi. GFP:PIP5K2 was rapidly turned over by proteasomal activity in planta, and overexpression of YFP:PIP5K2 caused pleiotropic growth abnormalities in transgenic Arabidopsis. We propose that plant cells exhibit a novel interaction in which PIP5K2 binds GTP-bound Rab-E proteins, which may stimulate temporally or spatially localized PtdIns(4,5)P2 production at the plasma membrane.

Key words: Ypt2, MG132, Proteasome, Root hair, PtdIns(4,5)P2, Secretion, MORN domain


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