Accumulation of soybean glycinin and its assembly with the glutelins in rice

Saline-soluble glycinins and insoluble glutelins are the major storage prot eins in soybean (Glycine mad and rice (Oryza sativa), respectively. In spit e of their differences in solubility properties, both proteins are members of the 11S globulin gene family based on their similarities in primary sequ ences and processing of the coded protein. Wild-type and methionine-modifie d glycinin coding sequences were expressed in transgenic rice plants under the control of the rice glutelin GluB-1 promoter. Glycinins were specifical ly synthesized in the endosperm tissue and co-localized with glutelins in t ype II protein bodies. They assembled into 7S and 11S species, similar to w hat was observed in developing soybean seeds. This pattern was quite differ ent from that displayed by the rice glutelins in untransformed plants, in w hich processed subunits sedimenting at 2S were apparent. In glycinin-expres sing transgenic plants, however, glutelins were observed sedimenting at 7S and 11S with lesser amounts in the 2S region. A portion of the glycinins wa s also found associated in the insoluble glutelin fraction. Renaturation ex periments suggested that the hybrid glycinin-glutelin oligomers were formed through specific interactions. Overall, these results indicate that despit e significant differences in the assembly of soybean glycinin and rice glut elin, both proteins can assemble with each other to form soluble hexameric oligomers or insoluble aggregates.