RESUMO
Rice seed storage proteins glutelin and α-globulin are synthesized in the endoplasmic reticulum (ER) and deposited in protein storage vacuoles (PSVs). Sar1, a small GTPase, acts as a molecular switch to regulate the assembly of coat protein complex II, which exports secretory protein from the ER to the Golgi apparatus. To reveal the route by which glutelin and α-globulin exit the ER, four putative Sar1 genes (OsSar1a/b/c/d) were cloned from rice, and transgenic rice were generated with Sar1 overexpressed or suppressed by RNA interference (RNAi) specifically in the endosperm under the control of the rice glutelin promoter. Overexpression or suppression of any OsSar1 did not alter the phenotype. However, simultaneous knockdown of OsSar1a/b/c resulted in floury and shrunken seeds, with an increased level of glutelin precursor and decreased level of the mature α- and ß-subunit. OsSar1abc RNAi endosperm generated numerous, spherical, novel protein bodies with highly electron-dense matrixes containing both glutelin and α-globulin. Notably, the novel protein bodies were surrounded by ribosomes, showing that they were derived from the ER. Some of the ER-derived dense protein bodies were attached to a blebbing structure containing prolamin. These results indicated that OsSar1a/b/c play a crucial role in storage proteins exiting from the ER, with functional redundancy in rice endosperm, and glutelin and α-globulin transported together from the ER to the Golgi apparatus by a pathway mediated by coat protein complex II.
Assuntos
alfa-Globulinas/metabolismo , Retículo Endoplasmático/metabolismo , Endosperma/metabolismo , Glutens/metabolismo , Proteínas Monoméricas de Ligação ao GTP/metabolismo , Oryza/enzimologia , Proteínas de Plantas/metabolismo , alfa-Globulinas/genética , Sequência de Aminoácidos , Retículo Endoplasmático/genética , Endosperma/genética , Glutens/genética , Dados de Sequência Molecular , Proteínas Monoméricas de Ligação ao GTP/química , Proteínas Monoméricas de Ligação ao GTP/genética , Oryza/classificação , Oryza/genética , Oryza/metabolismo , Filogenia , Proteínas de Plantas/química , Proteínas de Plantas/genética , Precursores de Proteínas/genética , Precursores de Proteínas/metabolismo , Transporte Proteico , Sementes/genética , Sementes/metabolismo , Alinhamento de SequênciaRESUMO
We analysed the global protein expression in seeds of a high-oil soybean cultivar (Jiyu 73, JY73) by proteomics. More than 700 protein spots were detected and 363 protein spots were successfully identified. Comparison of the protein profile of JY73 with that of a high-protein cultivar (Zhonghuang 13, ZH13) revealed 40 differentially expressed proteins, including oil synthesis, redox/stress, hydrolysis and storage-related proteins. All redox/stress proteins were less or not expressed in JY73, whereas the expression of the major storage proteins, nitrogen and carbon metabolism-related proteins was higher in ZH13. Biochemical analysis of JY73 revealed that it was in a low oxidation state, with a high content of polyunsaturated fatty acids and vitamin E. Vitamin E was more active than antioxidant enzymes and protected the soybean seed in a lower oxidation state. The characteristics of high oil and high protein in soybean, we revealed, might provide a reference for soybean nutrition and soybean breeding.