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An ARF-GEF acting at the Golgi and in selective endocytosis in polarized plant cells


Circumstantial evidence suggests that intracellular membrane trafficking pathways diversified independently in the plant kingdom1,2,3,4,5,6,7,8,9,10, but documented examples are rare6,11,12. ARF-GEFs (guanine-nucleotide exchange factors for ADP-ribosylation factor GTPases) are essential for vesicular trafficking in all eukaryotic kingdoms, but of the eight ARF-GEF families, only the ancestral BIG and GBF types are found in plants1,2. Whereas fungal and animal GBF proteins perform conserved functions at the Golgi, the Arabidopsis thaliana GBF protein GNOM is thought to act in only the process of recycling from endosomes3,4,5. We now show that the related Arabidopsis GBF protein GNOM-LIKE1 (GNL1) has an ancestral function at the Golgi but is also required for selective internalization from the plasma membrane in the presence of brefeldin A (BFA). We identified gnl1 mutants that accumulated biosynthetic and recycling endoplasmic reticulum markers in enlarged internal compartments. Notably, in the absence of functional GNL1, Golgi stacks were rendered sensitive to the selective ARF-GEF inhibitor BFA, which caused them to fuse with the endoplasmic reticulum. Furthermore, in BFA-treated gnl1 roots, the internalization of a polar plasma-membrane marker, the auxin efflux carrier PIN2, was selectively inhibited. Thus, GNL1 is a BFA-resistant GBF protein that functions with a BFA-sensitive ARF-GEF both at the Golgi and in selective endocytosis, but not in recycling from endosomes. We propose that the evolution of endocytic trafficking in plants was accompanied by neofunctionalization within the GBF family, whereas in other kingdoms it occurred independently by elaboration of additional ARF-GEF families.

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Figure 1: Phenotypes of gnl1 plants.
Figure 2: Golgi stacks in gnl1 are hypersensitive to BFA.
Figure 3: GNL1 is required for PIN2 accumulation in BFA bodies.

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We are indebted to S. Richter, Y.-D. Stierhof and G. Jürgens for generously providing plasmids and seeds with YFP-tagged GNL1, seeds of gnl1-1, antibodies, for sharing data before publication, and for discussions; A. Murphy for PIN2 antisera, advice on immunolocalization, and discussions; H. Zheng, who generated mutagenized secGFP(S76) seed; J. Denecke for anti-calreticulin/BiP antibody; and M. Bennett, M. Fricker, J. Pérez-Gomez, M. Grebe and J. Langdale for comments and discussions. We thank J. Baker and C. O’Brien for photographs and technical assistance. This work was supported by a studentship from the Malaysian Palm Oil Board (O.T.) and a grant from the BBSRC (I.M.).

Author Contributions O.T. isolated and characterized gnl1-2 and gnl1-3. I.M. assisted with imaging, wrote the paper and participated in discussions.

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Correspondence to Ian Moore.

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Supplementary Figures with Legends

This file contains Supplementary Figures S1 to S12 with Legends. These Supplementary Figures provide further detailed genetic and cellular characterisation of gnl1. (PDF 4773 kb)

Supplementary Table

This file contains Supplementary Table with details of image parameters used for each micrograph in Figures 1-3. (XLS 31 kb)

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Teh, Ok., Moore, I. An ARF-GEF acting at the Golgi and in selective endocytosis in polarized plant cells. Nature 448, 493–496 (2007).

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