title: Protein delivery to vacuole requires SAND protein-dependent Rab GTPase conversion for MVB-vacuole fusion.
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.
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Singh
authors.affiliation: Center for Organismal Studies (COS), University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Falco
authors.initials: F
authors.lastname: Krüger
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
authors.forename: Hauke
authors.initials: H
authors.lastname: Beckmann
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Brumm
authors.affiliation: Section Plant Physiology, University of Amsterdam, Swammerdam Institute for Life Sciences, 1098 SM, Amsterdam, the Netherlands.
authors.forename: Joop E M
authors.initials: JEM
authors.lastname: Vermeer
authors.affiliation: Section Plant Physiology, University of Amsterdam, Swammerdam Institute for Life Sciences, 1098 SM, Amsterdam, the Netherlands.
authors.forename: Teun
authors.initials: T
authors.lastname: Munnik
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Microscopy, University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Mayer
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Microscopy, University of Tübingen, 72076 Tübingen, Germany.
authors.forename: York-Dieter
authors.initials: YD
authors.lastname: Stierhof
authors.affiliation: Center for Plant Molecular Biology (ZMBP), Developmental Genetics, University of Tübingen, Auf der Morgenstelle 32, 72076 Tübingen, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Grefen
authors.affiliation: Center for Organismal Studies (COS), University of Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Schumacher
authors.affiliation: 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.
authors.forename: Gerd
authors.initials: G
authors.lastname: Jürgens
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008247:Lysosomes / Q000378:metabolism; D057146:Multivesicular Bodies / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D014617:Vacuoles / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D009687:Nuclear Proteins; C000601166:SAND protein, Arabidopsis; C495672:Ara7 protein, Arabidopsis; D020691:rab GTP-Binding Proteins