The rice RMR1 associates with a distinct prevacuolar compartment for the protein storage vacuole pathway.

Transport of vacuolar proteins from Golgi apparatus or trans-Golgi network (TGN) to vacuoles is a receptor-mediated process via an intermediate membrane-bound prevacuolar compartment (PVC) in plant cells. Both vacuolar sorting receptor (VSR) and receptor homology region-transmembrane domain-RING-H2 proteins have been shown to function in transporting storage proteins to protein storage vacuole (PSV), but little is known about the nature of the PVC for the PSV pathway. Here, we use the rice as a probe to study the PSV pathway in plants. Immunogold electron microscopy (EM) with specific antibodies showed that Osduanyu17481 proteins were found in the Golgi apparatus, TGN, and a distinct organelle with characteristics of PVC in both rice culture cells and developing rice seeds, as well as the protein body type II (PBII) or PSV in developing rice seeds. This organelle, also found in both tobacco BY-2 and Arabidopsis suspension cultured cells, is morphologically distinct from the VSR-positive multivesicular lytic PVC or multivesicular body (MVB) and thus represent a PVC for the PSV pathway that we name storage PVC (sPVC). Further in vivo and in vitro interaction studies using truncated Osduanyu17481 proteins secreted into the culture media of transgenic BY-2 suspension cells demonstrated that Osduanyu17481 functions as a sorting receptor in transporting vicilin-like storage proteins.

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