Characterization of 40 soybean (Glycine max) promoters, isolated from across 5 thematic gene groups

Gene expression in plants is primarily modulated by the promoter region, which is located upstream of the gene coding region. Specific regulatory sequences within the promoter region contribute to the strength, tissue specificity, timing and duration of gene expression. In this study, promoter regions were isolated from 40 different soybean (Glycine max) genes that were grouped into five distinct categories, based on the localization of native gene expression (constitutively expressed genes, root-preferentially expressed genes, seed-preferentially expressed genes), or the associated biological processes of native gene expression (fatty-acid biosynthesis pathway associated genes, and WRKY transcription factor genes). Each of the promoters was placed upstream of the green fluorescent protein coding sequence and promoter functionality was then assessed using transient expression analysis following particle bombardment of lima bean (Phaseolus lunatus) cotyledons, as well as stable expression analysis following Agrobacterium rhizogenes induction of soybean hairy roots. Surprisingly, promoter strength was relatively consistent using the two different validation methods while tissue specific expression was not observed, likely due to a combination of the target tissue, the large amount of DNA that was introduced and minimal epigenetic effects. The differences in gene expression within members of each promoter group indicates that promoters need to be characterized in a transgenic environment, rather than relying on expression predicted using native gene expression profiles. This systematic approach into the characterization of native soybean promoters adds to the knowledge base of soybean gene regulation and the toolbox of promoters for plant biotechnology.