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Curr Biol. 2014 Jun 16;24(12):1383-1389. doi: 10.1016/j.cub.2014.05.005. Epub 2014 May 29.

Protein delivery to vacuole requires SAND protein-dependent Rab GTPase conversion for MVB-vacuole fusion.

Author information

1
Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
2
Center for Organismal Studies (COS), University of Heidelberg, 69120 Heidelberg, Germany.
3
Section Plant Physiology, University of Amsterdam, Swammerdam Institute for Life Sciences, 1098 SM, Amsterdam, the Netherlands.
4
Center for Plant Molecular Biology (ZMBP), Microscopy, University of Tübingen, 72076 Tübingen, Germany.
5
Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany. Electronic address: gerd.juergens@zmbp.uni-tuebingen.de.

Abstract

Plasma-membrane proteins such as ligand-binding receptor kinases, ion channels, or nutrient transporters are turned over by targeting to a lytic compartment--lysosome or vacuole--for degradation. After their internalization, these proteins arrive at an early endosome, which then matures into a late endosome with intraluminal vesicles (multivesicular body, MVB) before fusing with the lysosome/vacuole in animals or yeast. The endosomal maturation step involves a SAND family protein mediating Rab5-to-Rab7 GTPase conversion. Vacuolar trafficking is much less well understood in plants. Here we analyze the role of the single-copy SAND gene of Arabidopsis. In contrast to its animal or yeast counterpart, Arabidopsis SAND protein is not required for early-to-late endosomal maturation, although its role in mediating Rab5-to-Rab7 conversion is conserved. Instead, Arabidopsis SAND protein is essential for the subsequent fusion of MVBs with the vacuole. The inability of sand mutant to mediate MVB-vacuole fusion is not caused by the continued Rab5 activity but rather reflects the failure to activate Rab7. In conclusion, regarding the endosomal passage of cargo proteins for degradation, a major difference between plants and nonplant organisms might result from the relative timing of endosomal maturation and SAND-dependent Rab GTPase conversion as a prerequisite for the fusion of late endosomes/MVBs with the lysosome/vacuole.

PMID:
24881875
DOI:
10.1016/j.cub.2014.05.005
[Indexed for MEDLINE]
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