Co-expression of alpha' and beta subunits of beta-conglycinin in rice seeds and its effect on the accumulation behavior of the expressed proteins.

A transgenic rice that produces both the alpha' and beta subunits of beta-conglycinin has been developed through the crossing of two types of transgenic rice. Although the accumulation level of the alpha' subunit in the alpha'beta-transgenic rice was slightly lower than that in the transgenic rice producing only the alpha' subunit, the accumulation level of the beta subunit in the alpha'beta-transgenic rice was about 60% higher than that in the transgenic rice producing only the beta subunit. Results from sequential extraction and gel-filtration experiments indicated that part of the beta subunit formed heterotrimers with the alpha' subunit in a similar manner as in soybean seeds and that the heterotrimers interacted with glutelin via cysteine residues. These results imply that the accumulation level of the beta subunit in the alpha'beta-transgenic rice increases by an indirect interaction with glutelin. Immunoelectron microscopy revealed that the alpha' and beta subunits are localized in a low electron-dense region of protein body-II (PB-II) and that alpha' homotrimers in the alpha'beta-transgenic rice seeds seem to accumulate outside of this low electron-dense region.