Different effects on triacylglycerol packaging to oil bodies in transgenic rice seeds by specifically eliminating one of their two oleosin isoforms.

Expression of OLE16 and OLE18, two oleosin isoforms in oil bodies of rice seeds, was suppressed by RNA interference. Electron microscopy revealed a few large, irregular oil clusters in 35S::ole16i transgenic seed cells, whereas accumulated oil bodies in 35S::ole18i transgenic seed cells were comparable to or slightly larger than those in wild-type seed cells. Large and irregular oil clusters were observed in cells of double mutant seeds. These unexpected differences observed in oil bodies of 35S::ole16i and 35S::ole18i transgenic seeds were further analyzed. In comparison to wild-type plants, OLE18 levels were reduced to approximately 40% when OLE16 was completely eliminated in 35S::ole16i transgenic plants. In contrast, OLE16 was reduced to only 80% of wild-type levels when OLE18 was completely eliminated in 35S::ole18i transgenic plants. While the triacylglycerol content of crude seed extracts of 35S::ole16i and 35S::ole18i transgenic seeds was reduced to approximately 60% and 80%, respectively, triacylglycerol in isolated oil bodies was respectively reduced to 45% and 80% in accordance with the reduction of their oleosin contents. Oil bodies isolated from both 35S::ole16i and 35S::ole18i transgenic seeds were found to be of comparable size and stability to those isolated from wild-type rice seeds, although they were merely sheltered by a single oleosin isoform. The drastic difference between the triacylglycerol contents of crude seed extracts and isolated oil bodies from 35S::ole16i transgenic plants could be attributed to the presence of large, unstable oil clusters that were sheltered by insufficient amounts of oleosin and therefore could not be isolated together with stable oil bodies.