A PUTATIVE VACUOLAR CARGO RECEPTOR PARTIALLY COLOCALIZES WITH ATPEP12P ON A PREVACUOLAR COMPARTMENT IN ARABIDOPSIS ROOTS

Targeting of protein cargo to the vacuole/ lysosome is a multistep pro cess that appears to have conserved features between mammalian, yeast, and plant cells. In each case, some soluble vacuolar/lysosomal protei ns are believed to be bound by transmembrane cargo receptors in the tr ans-Golgi network (TGN) that redirect these proteins into clathrin-coa ted vesicles. These vesicles then appear to be transported to the prev acuole/endosome by a trafficking machinery that requires components id entified in other vesicle-targeting steps such as N-ethglmaleimide-sen sitive factor (NSF), soluble NSF attachment protein (SNAP), SNAP recep tors (SNAREs), rab-type GTPases, and Sec1p homologs. Two likely member s of this trafficking machinery have been characterized from Arabidops is thaliana: AtPEP12p, a t-SNARE that resides on a what we now call a prevacuolar compartment, and AtELP, a protein that shares many common features with mammalian and yeast transmembrane cargo receptors. Here, we have further investigated the intracellular distribution of AtELP. We have found that AtELP is located at the trans-Golgi of Arabidopsis root cells, and that its C terminus can preferentially interact in vi tro with the mammalian TGN-specific AP-1 clathrin-adapter complex, sug gesting a likely role in clathrin-coated, vesicle-directed trafficking at the TGN. Further, consistent with a role in trafficking of vacuola r cargo, we have found that AtELP partially colocalizes with AtPEP12p on a prevacuolar compartment.