Arabidopsis VPS35, a Retromer Component, is Required for Vacuolar Protein Sorting and Involved in Plant Growth and Leaf Senescence

The retromer complex is responsible for retrograde transport, which is coordinated with anterograde transport in the secretory pathway including vacuolar protein sorting. Yeast VPS35 is a component of the retromer complex that is essential for recognition of specific cargo molecules. The physiological function of VPS35 has not been determined in vacuolar protein sorting in higher organisms. Arabidopsis thaliana has three VPS35 homologs designated VPS35a, VPS35b and VPS35c. We isolated four vps35 mutants (vps35a-1, vps35b-1, vps35b-2 and vps35c-1) and then generated four double mutants and one triple mutant. vps35a-1 vps35c-1 exhibited no unusual phenotypes. On the other hand, vps35b-1 vps35c-1 and the triple mutant (vps35a-1 vps35b-2 vps35c-1) exhibited severe phenotypes: dwarfism, early leaf senescence and fragmentation of protein storage vacuoles (PSVs). In addition, these mutants mis-sorted storage proteins by secreting them out of the cells and accumulated a higher level of vacuolar sorting receptor (VSR) than the wild type. VPS35 was localized in pre-vacuolar compartments (PVCs), some of which contained VSR. VPS35 was immunoprecipitated with VPS29/MAG1, another component of the retromer complex. Our findings suggest that VPS35, mainly VPS35b, is involved in sorting proteins to PSVs in seeds, possibly by recycling VSR from PVCs to the Golgi complex, and is also involved in plant growth and senescence in vegetative organs.