title: Functional diversification of closely related ARF-GEFs in protein secretion and recycling.
abstract: Guanine-nucleotide exchange factors on ADP-ribosylation factor GTPases (ARF-GEFs) regulate vesicle formation in time and space by activating ARF substrates on distinct donor membranes. Mammalian GBF1 (ref. 2) and yeast Gea1/2 (ref. 3) ARF-GEFs act at Golgi membranes, regulating COPI-coated vesicle formation. In contrast, their Arabidopsis thaliana homologue GNOM (GN) is required for endosomal recycling, playing an important part in development. This difference indicates an evolutionary divergence of trafficking pathways between animals and plants, and raised the question of how endoplasmic reticulum-Golgi transport is regulated in plants. Here we demonstrate that the closest homologue of GNOM in Arabidopsis, GNOM-LIKE1 (GNL1; NM_123312; At5g39500), performs this ancestral function. GNL1 localizes to and acts primarily at Golgi stacks, regulating COPI-coated vesicle formation. Surprisingly, GNOM can functionally substitute for GNL1, but not vice versa. Our results suggest that large ARF-GEFs of the GBF1 class perform a conserved role in endoplasmic reticulum-Golgi trafficking and secretion, which is done by GNL1 and GNOM in Arabidopsis, whereas GNOM has evolved to perform an additional plant-specific function of recycling from endosomes to the plasma membrane. Duplication and diversification of ARF-GEFs in plants contrasts with the evolution of entirely new classes of ARF-GEFs for endosomal trafficking in animals, which illustrates the independent evolution of complex endosomal pathways in the two kingdoms.
authors.affiliation: ZMBP, Entwicklungsgenetik, Tübingen, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Richter
authors.forename: Niko
authors.initials: N
authors.lastname: Geldner
authors.forename: Jarmo
authors.initials: J
authors.lastname: Schrader
authors.forename: Hanno
authors.initials: H
authors.lastname: Wolters
authors.forename: York-Dieter
authors.initials: YD
authors.lastname: Stierhof
authors.forename: Gabino
authors.initials: G
authors.lastname: Rios
authors.forename: Csaba
authors.initials: C
authors.lastname: Koncz
authors.forename: David G
authors.initials: DG
authors.lastname: Robinson
authors.forename: Gerd
authors.initials: G
authors.lastname: Jürgens
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D020126:Brefeldin A / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D005816:Genetic Complementation Test; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D021381:Protein Transport / Q000187:drug effects; D011506:Proteins / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C522273:GNL1 protein, Arabidopsis; C088087:GNOM protein, Arabidopsis; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D020126:Brefeldin A; D020727:ADP-Ribosylation Factors