Osmotic stress-induced CsRCI2E endosomal trafficking promotes the redistribution of aquaporin CsPIP2 at the plasma membrane of Camelina sativa L.

Abstract Rare Cold Inducible 2s (RCI2s) are proteolipids that travel from the plasma membrane (PM) to the endomembrane. The expression of RCI2s is induced by abiotic stresses such as cold, heat, drought, and salinity and affects abiotic stress tolerance in plants. It has been reported that CsRCI2E interacts with the water transport protein CsPIP2;1 to reduce its abundance at the PM during NaCl stress. Therefore, CsRCI2E is considered a potential factor affecting the endocytosis of CsPIP2s for maintaining cell homeostasis; however, its exact function in membrane trafficking remains unclear. In this study, we observed the rapid internalization of CsRCI2E and CsPIP2s under both mannitol- and NaCl-induced osmotic stresses using a sucrose density gradient. The transcription of CsRCI2Eincreased markedly 3 h after treatment with mannitol or NaCl. The over-expression of CsRCI2E enhanced stress tolerance and reduced cell damage from reactive oxygen species accumulation in germinating Camelina. Interestingly, the subcellular distribution of CsRCI2E and CsPIP2s shifted rapidly from the PM to the endomembrane within 0.5 h after both osmotic shocks even though the CsRCI2E gene expression had not been changed by the stresses at that time. Additionally, CsRCI2Eoverexpression caused the internalization and subcellular redistribution of CsRCI2E and CsPIP2 under osmotic stress conditions as well as no stress conditions. These results suggest that the internalization of CsRCI2E is a sensing mechanism in the early stages of osmotic shock. Furthermore, an increased amount of CsRCI2E promotes the membrane trafficking of CsPIP2 from the PM to the endomembrane to maintain water homeostasis in Camelina.