Tissue-specific and temporal regulation of a beta-conglycinin gene: roles of the RY repeat and other cis-acting elements.

Upstream regulatory sequences (URS) of the gene that encodes the alpha' subunit of beta-conglycinin, the 7S soybean seed storage protein, includes two RY repeat elements. The role of RY elements and sequences that bind soybean embryo factors 3 and 4 (SEF3 and SEF4; Allen et al., Plant Cell 1 (1989) 623-631) in regulating expression of the promoter was studied following site directed mutagenesis. Specific mutations introduced into these sequences abolished the in vitro binding activities of SEF3 and SEF4. The biological activities resulting from the mutations were determined in transgenic plants using two chimeric promoters comprising sequences from the CaMV 35S promoter and the alpha' subunit promoter. The uidA reporter gene was used to assess the levels of gene expression in transgenic plants. The mutations in the RY element and SEF3 and SEF4 binding sites had little effect on expression of the alpha' promoter. By contrast, mutations in the RY element had significant effect on gene expression when the URS from the alpha' promoter was ligated upstream of the core 35S promoter. Mutations in the RY element abolished the seed specific enhancing activity of the alpha' URS and caused expression of the chimeric promoter in leaves. These results indicate that the RY element plays a key role in seed-specific gene regulation in coordination with other cis-acting elements.