Inheritance of Novel 57H Mutations in Rice and Their Effect on Compartmentation of Endosperm Storage Proteins

Prolamins and glutelins, synthesized in the ER, are compartmentalized into individual protein bodies (PB), the ER‐derived PB‐I and the vacuolar PB‐II in wild‐type rice, respectively. Six 57H mutants with high amounts of 57 kD glutelin precursor were isolated by screening 3000 N‐methyl‐N‐nitrosourea‐induced mutants of the rice cultivar TC65. SDS‐PAGE and immunoblot analyses of storage proteins showed that some of the mutants contained not only the high amount of glutelin precursor and the corresponding low amounts of mature glutelin subunits but also the low amounts of the b species of 13 kD prolamins in comparison with the TC65 cultivar. The protein alterations in each mutant were found to result from a recessive mutation of a single gene in each. One mutation among them was identified to be a novel gene, glup6, nonallelic to the reported 57H mutant genes. EM observation showed the existence of the ER‐derived mutant PB and the vacuolar PB‐II in endosperm cells of glup6. The PB mutant was stained to a different degree in its core and the peripheral region, and it was decreased in size compared with the wild‐type PB‐I. Immunocytochemical analysis showed that the glutelin precursor was deposited with 13b kD prolamin in the peripheral region of the PB mutant. These results indicate that the glup6 inhibits sorting of the glutelin precursor polypeptide and the prolamin polypeptide within the ER. The analysis results of the glup6esp2 mutant showed that the effect of glup6 is hypostatic to the esp2 mutation in the compartmentation of glutelins and prolamins.