Structure and activity of a soybean Adh promoter in transgenic hairy roots

Abstract

The alcohol dehydrogenase (Adh) gene in plants is transcriptionally induced by anoxia and hypoxia. The Adh gene family consists of one to four members, depending on the plant species. The developmental expression and tissue-specific responses of each gene member to hypoxic stress have been well documented. In addition to hypoxia, the Adh gene is also induced by heat, dehydration, cold, and treatment with the hormone abscisic acid (ABA). Extensive studies of the structure and function of the maize (Zea mays L.) Adh promoters have identified several common motifs that are essential for the proper responses to environmental stimuli. The structure and expression of the soybean (Glycine max L. Merr.) Adh promoter have not been as well documented as in maize and Arabidopsis. In this study, we isolated a 976-bp fragment upstream of the soybean Adh2 gene start codon. The putative promoter contains motifs homologous to the anaerobiosis responsive element and the G-box-1 palindromic element characteristic of known Adh promoters. The putative promoter was fused with the β-glucuronidase (GUS) reporter gene, and the pBI-Adh:GUS plasmid was introduced into soybean hairy roots by Agrobacterium rhizogenes-mediated transformation of cotyledons. GUS activity assay and histochemical staining of the five transgenic Adh:GUS hairy root lines indicated that the promoter was inducible by anoxia but did not respond to cold temperature, wounding or ABA treatment. GUS expression in transgenic 35S:GUS hairy root lines was not affected by anoxia, cold, wounding, or ABA. The Adh promoter may be useful in transformation experiments where the hypoxically induced expression of the transgenes is needed to improve the plant's tolerance to flooding or hypoxia stress.