Expression of the β-subunit of β-conglycinin in seeds of transgenic plants

Soybean (Glycine max (L.) Merr.) seeds contain the storage protein β-conglycinin, encoded by a multigene family. β-Conglycinin consists of three subunits; α', α, and β. A genomic clone for a β-subunit of β-conglycinin has been characterized by restriction-enzyme mapping and hybrid selected in-vitro translation followed by immunoprecipitation. In order to determine the developmental regulation of this β-subunit gene, its expression was studied in seeds of transgenic petunia (Petunia hybrida) and tobacco (Nicotiana tabacum L.) plants. The β-subunit expressed in seeds of petunia and tobacco was recognized by anti-β-conglycinin serum at a relative molecular mass of 53 000, equivalent to that of the native protein. Separation of the petunia-seed proteins by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis showed that multiple isoelectric forms of the β-subunit were produced. There was approximately a twofold variation in the accumulation of the β-subunit protein in the mature seeds of transgenic petunia plants, each containing a single β-subunit gene. However, the level of protein accumulation in mature seeds and the amount of β-subunit mRNA in developing seeds was not correlated. Accumulation of the β-subunit protein in transgenic seeds was less than the α'-subunit protein that accumulated in transgenic petunia seeds containing a single α'-subunit gene and less than the amount of the β-subunit in mature soybean seeds which contain 8-13 β-subunit genes. In transgenic tobacco plants, the accumulation of the β-subunit protein in seeds was generally well correlated with the number of genes that were incorporated in the different transformants.