A Vigna radiata 8S Globulin α′ Promoter Drives Efficient Expression of GUS in Arabidopsis Cotyledonary Embryos

Plants are proven effective bioreactors for the production of heterologous proteins including those desired by the biopharmaceutical industry. However, the potential of plants as bioreactors is limited by the availability of characterized plant promoters that can drive target gene expression in relatively distant plant species. Seeds are ideal for protein storage because seed proteins can be kept stably for several months. Hence, a strong promoter that can direct the expression and accumulation of target proteins within seeds represents a powerful tool in plant biotechnology. Toward this end, an effort was made to identify such a promoter from Vigna radiata (mung bean) to drive expression in dicot seeds. A 784-bp 5'-flanking sequence of the gene encoding the 8S globulin alpha' subunit (8SG alpha') of the V. radiata seed storage protein was isolated by genome walking. When the 5'-flanking region was analyzed with bioinformatics tools, numerous putative cis-elements were identified. The Green Fluorescent Protein (GFP) regulated by this promoter was observed to be transiently expressed in protoplasts derived from V. radiata cotyledons. Finally, transgenic Arabidopsis plants expressing the beta-glucuronidase (GUS) reporter gene driven from the 8S globulin alpha' promoter showed strong GUS expression in transgenic embryos in both histochemical and quantitative GUS assays, confirming high expression within seeds. Therefore, the V. radiata 8S alpha' promoter has shown potential in directing expression in seeds for bioreactor applications.