Genetic evidence that the higher plant Rab-D1 and Rab-D2 GTPases exhibit distinct but overlapping interactions in the early secretory pathway.
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.
Pinheiro
Hazel
H
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
Samalova
Marketa
M
Geldner
Niko
N
Chory
Joanne
J
Martinez
Alberto
A
Moore
Ian
I
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D005799:Genes, Dominant; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D010641:Phenotype; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D055571:Secretory Pathway; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D021601:trans-Golgi Network / Q000201:enzymology
D029681:Arabidopsis Proteins; C546290:Rab-D2 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; C533032:RabD1 protein, Arabidopsis; D020559:Monomeric GTP-Binding Proteins; D020691:rab GTP-Binding Proteins