Differential expression of conglycinin ?? and ? subunit genes in transgenic plants

Abstract

β-conglycinin or 7S protein, one of the two major storage proteins of soybean (Glycine max), is comprised of three subunits, α′, α and β. Genomic clones encoding the α′ and β subunit genes were ligated together in intermediate plasmids, either in direct orientation (← ←) or in divergent orientation (← →). In the latter instance the transcriptional promoters of the two genes were approximately 2.0 kb apart. The DNAs were introduced into leaf disks of Petunia hybrida on a disarmed Ti plasmid in Agrobacterium tumefaciens and transgenic plants were regenerated. Expression of the introduced genes, limited to specific stages in developing seeds, was analyzed by quantitating the accumulated mRNA and protein, and compared with expression in transgenic plants that contained either gene alone. Development time course studies showed that the α′ subunit mRNA and protein were first detected at 10 days after pollination while accumulation of the β subunit protein ensued at day 14 regardless of the orientation of the two genes. The temporally regulated expression of these two genes in transgenic plants mimics their temporal regulation during soybean embryo development. In transgenic plants that contain the α′ and β genes in divergent orientation, expression of the β gene was enhanced several-fold, while the expression of the α′ gene was slightly decreased. These results suggest that (i) sequences of the α′ gene enhance the level of expression of a nearby storage protein gene and that (ii) the signal(s) operating in the temporal regulation of seed storage protein genes is (are) common to soybean and petunia, and are different from those that govern the final amounts of mRNA and protein.