Genetic mechanism controlling the transportation and accumulation of glutelin into protein body in rice endosperm

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To elucidate the mechanism of intracellular transportation and accumulation of rice seed storage protein, 130 Iines of 57H mutant, which are characterized by the increased amount of proglutelin with 57 kD, were produced and novel 4 genes for 57H trait were identified. Based on genetic and histochemical analyses of the mutants, the function of each gene was discussed.-Mutation for the sorting of storage proteins within endoplasmic reticulum (ER), Type1 mutation The analysis of esp2 mutation deleted PDI demonstrated that PDI was indispensable for the sorting of proglutelin precursor and prolamin within ER Iumen. glup4 and glup6 mutations also were classified into Type1 mutation, showing that at least 3 genes participate in the sorting of both proteins within ER lumen.-Mutation for transportation from ER to protein storage vacuole (PSV), Type2 mutation In Type2 mutation, proglutelin precursor and prolamin were accumulated into separated particles within ER derived PB. Glup1, glup2, Glup5, glup7, Glup8 mutations were classified into Type2 mutation, showing that at least 5 genes participate in the transportation of proglutelin from ER lumen to PSV.-Mutation for proteolysis within PSV. Type3 mutation The analysis of glup3 mutation demonstrated that VPE was indispensable for proteolytical cleavage of proglutelin precursor within PSV. glup3 mutation accumulated the progiutelin and the cleaved form of glutelin in PSV together, showing that at least 2 VPEs participate in proteolysis of proglutelin precursor.These results demonstrated that the pathway of transportation and accumulation of glutelin in seed was divided into steps and that the genes regulating each step were 1) Targeting of glutelin mRNA to cis-ER, 2) Sorting of proglutelin precursor within ER lumen, Esp2 (PDI), Glup4, Glup6, 3) Transportation of proglutelin precursor into PSV, glupl, Glup2, glup5, Glup7, glup8, 4) Proteolysis of proglutelin precursor within PSV, Glup3 (VPE),