Molecular Plant Advance Access originally published online on October 3, 2008
Molecular Plant 2008 1(6):961-976; doi:10.1093/mp/ssn057
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Overexpression of Arabidopsis Sorting Nexin AtSNX2b Inhibits Endocytic Trafficking to the Vacuole
a Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011, USA
b Interdepartmental Genetics Program, Iowa State University, Ames, IA 50011, USA
c Plant Sciences Institute, Iowa State University, Ames, IA 50011, USA
1 To whom correspondence should be addressed. E-mail bassham{at}iastate.edu, fax 515-294-1337, tel. 515-294-7461.
Sorting nexins are conserved proteins that function in vesicular trafficking and contain a characteristic phox homology (PX) domain. Here, we characterize the ubiquitously expressed Arabidopsis thaliana sorting nexin AtSNX2b. Sub-cellular fractionation studies indicate that AtSNX2b is peripherally associated with membranes. The AtSNX2b PX domain binds to phosphatidylinositol 3-phosphate in vitro and this association is required for the localization of GFP–AtSNX2b to punctate structures in vivo, identified as the trans-Golgi network, prevacuolar compartment and endosomes. Overexpression of GFP-tagged AtSNX2b produces enlarged GFP-labeled compartments that can also be labeled by the endocytic tracer FM4-64. Endocytic trafficking of FM4-64 to the vacuole is arrested in these GFP–AtSNX2b compartments, and similar FM4-64-accumulating compartments are seen upon overexpression of untagged AtSNX2b. This suggests that exit of membrane components from these enlarged or aggregated endosomes is inhibited. Vacuolar proteins containing an N-terminal propeptide, but not those with a C-terminal propeptide, are also present in these enlarged compartments. We hypothesize that AtSNX2b is involved in vesicular trafficking from endosomes to the vacuole.