In the wild type of rice endosperm cell, glutelins and prolamins are synthesized on the respective subdomains of rough endoplasmic-reticulum (ER) and intracellularly compartmentalized into the different storage protein bodies, respectively. Herein, we first report a rice mutation involved in the biogenesis of glutelins and prolamins. A novel mutant for storage proteins was isolated and characterized by the great generation of 57 kD glutelin precursors (proglutelins) and the lacking of 13 kD prolamins. The proteinous alteration was clarified to result from a monogenic mutation with the dosage effect on generation of proglutelins and 13 kD prolamins. This mutation is referred to as GPGG1. A novel ER, the saccular composite-ER, was shown to act in the synthesis of proglutelins and 14 kD prolamins in the mutant. In addition to the composite-ER, the mutant type Golgi, trans-Golgi network, endocytotic protein-storage-vacuole, multivesicular body and lytic vacuole were shown to occur and function in the transfer, exocytosis, endocytosis, delivery, deposition and degradation of storage proteins in the mutant. Moreover, the GPGG1 gene was mapped to a 63.8-kb region of chromosome 12, and a pentatricopeptide repeat-like gene was determined as its candidate gene. Our results reveals that the GPGG1 was involved in the storage protein synthesis and caused the remodeling of endomembrane system for storage protein compartmentation. The candidate gene presumably concerns translation of storage protein mRNAs in rice endosperm cells.

Glutelins and prolamins, the main rice storage proteins, are synthesized in the ER and accumulated into the vacuolar protein body and the ER-derived protein body in endosperm cell of the developing seed of the wild type rice, respectively. Several 57H mutations have been found to cause the high increase of 57 kD glutelin precursor and the remarkable decrease of the mature glutelins, and involved in the accumulation of storage proteins in rice. In this study, two 57H mutants were newly found and obtained from rice germplasms using SDS-PAGE technique. SDS-PAGE analysis of the total seed proteins showed that the two mutants had the characters namely the great increase of 57 kD polypeptide and the lack of 13 kD polypeptide, but not alteration of characters for the mature glutelins and other storage proteins; Electrophoretic and immuno-blotting analyses of glutelin showed that the increased polypeptides was 57 kD glutelin precursor in the mutants; Electrophoretic analysis of prolamins showed that the lacked polypeptide was 13 kD prolamin in them. It is indicate that the two mutants have novel characters distinct from the reported 57H mutants. They probably contain unknown genetic information for synthesis and expression of storage proteins, and are considered to be useful materials for the overall understanding of genetic mechanism regulating synthesis and accumulation of the storage proteins in rice.