Abstract
The 11 rice OsPIP aquaporins are grouped into the OsPIP1 and OsPIP2 subfamilies. We previously showed that OsPIP1s have low water permeability in Xenopus oocytes but this could be increased by OsPIP2 coexpression. Furthermore, the small proportion of OsPIP1-EGFP proteins targeted to the oocyte plasma membrane (PM) could be increased by OsPIP2 coexpression. To further investigate these phenomena, we studied the subcellular localization of OsPIP1 and OsPIP2 subfamilies fused to EGFP or DsRed in Oc cell-derived protoplasts. In contrast to PM-localized OsPIP2, most OsPIP1s were found in the endoplasmic reticulum (ER), and their movement to the PM was promoted only with OsPIP2 coexpression. The subcellular colocalization of the two subfamilies was analysed using a modified Fluo-chase method. OsPIP1;1 and OsPIP2;1 interactions occurred at the ER by 24 h and at the PM by 72 h. Homomeric OsPIP1;1s remained targeted to the ER even after 72 h. The homomerized OsPIP2;1s population was less than the OsPIP1;1 and OsPIP2;1 heteromerized population at the PM. These results indicate that intracellular trafficking of OsPIP1 members is due to their association with OsPIP2s.
