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First published online 29 September 2009
doi: 10.1242/jcs.050625

Journal of Cell Science 122, 3749-3758 (2009)
Published by The Company of Biologists 2009
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Research Article

Genetic evidence that the higher plant Rab-D1 and Rab-D2 GTPases exhibit distinct but overlapping interactions in the early secretory pathway

Hazel Pinheiro1,*, Marketa Samalova1, Niko Geldner2,3, Joanne Chory3, Alberto Martinez4 and Ian Moore1,{ddagger}

1 Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK
2 Department of Plant Molecular Biology, Biophore, UNIL-Sorge, University of Lausanne, 1015 Lausanne, Switzerland
3 The Salk Institute, PBIO-C, 10010 North Torrey Pines Road, La Jolla, CA 92036, USA
4 Syngenta, Jealott's Hill Research Station, Bracknell, Berkshire RG42 6ET, UK

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

Accepted 3 August 2009

GTPases of the Rab1 subclass are essential for membrane traffic between the endoplasmic reticulum (ER) and Golgi complex in animals, fungi and plants. Rab1-related proteins in higher plants are unusual because sequence comparisons divide them into two putative subclasses, Rab-D1 and Rab-D2, that are conserved in monocots and dicots. We tested the hypothesis that the Rab-D1 and Rab-D2 proteins of Arabidopsis represent functionally distinct groups. RAB-D1 and RAB-D2a each targeted fluorescent proteins to the same punctate structures associated with the Golgi stacks and trans-Golgi-network. Dominant-inhibitory N121I mutants of each protein inhibited traffic of diverse cargo proteins at the ER but they appeared to act via distinct biochemical pathways as biosynthetic traffic in cells expressing either of the N121I mutants could be restored by coexpressing the wild-type form of the same subclass but not the other subclass. The same interaction was observed in transgenic seedlings expressing RAB-D1 [N121I]. Insertional mutants confirmed that the three Arabidopsis Rab-D2 genes were extensively redundant and collectively performed an essential function that could not be provided by RAB-D1, which was non-essential. However, plants lacking RAB-D1, RAB-D2b and RAB-D2c were short and bushy with low fertility, indicating that the Rab-D1 and Rab-D2 subclasses have overlapping functions.

Key words: AtRab1b, ARA5, Ypt1, Rab GTPases, pOp6/LhGR


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