Promoters are essential regulatory elements for efficiently expressing a gene of interest in a target tissue of a organism. Therefore, the identification of a suitable promoter is important in plant biotechnology. In this study, four promoters were selected and identified to be constitutively or tissue-specifically expressed in Brassica rapa bacterial artificial chromosome (BAC) clones using the results of transcriptomic analysis of Brassica rapa and open-source database information on Arabidopsis thaliana. The 2 kb region of the 5′ upstream was isolated from the Brassica rapa genomic DNA for each promoter. The four promoters were then fused to β-glucuronidase (gus) and green fluorescent protein (gfp) genes, and the recombinant transgenes were introduced into Arabidopsis. As a result of histochemical GUS staining, GFP fluorescence and RT-PCR, the gus gene was observed to be expressed constitutively in all tissues using all four promoters. A GUS activity assay using fluorescent 4-MUG revealed that the BR11 promoter showed similar activity to the CaMV35S promoter, while the BR4, BR15, and BR16 promoters showed 1.5, 4, and 18-fold higher activities than the CaMV35S promoter, respectively. These results indicate that these four promoters could be used to incorporate useful genes with enhanced function into crops of interest.

To identify and apply tissue-specific promoters is one of the major challenges in plants genetic engineering for optimizing efficient expression of interest genes in appropriate tissues. In this research, open-source database information of Arabidopsis thaliana was adapted to determine root-specific expressed promoter region. A total seven sequences that might function as a root-specific promoter element were initially isolated from Arabidopsis genomic DNA. Then seven promoters were cloned into pBGWFS7 in which β-glucuronidase (gus) and green fluorescent protein (gfp) genes were linked. The GUS activities were measured in different tissues of transgenic Arabidopsis by both histochemical GUS staining and fluorescent 4 methylumbelliferyl β-D-glucuronide (MUG) assay. To confirm root-specific expression, GFP-confocal microscope analysis was conducted in Arabidopsis transgenic plant. As a result, the five promoters showed strong GUS activity in the root tissue as compared with the CaMV35S promoter. To test crop application availability as a root-specific promoter, seven promoters were introduced into tomato plants and confirmed transient expression using Agrobacterium rhizogenesis ARqua1 root-nodule inducible strain. Two promoters showed that gus genes were specifically expressed in roots of transgenic tomato plant. Taken together, the novel seven promoters showed specific activity in root suggesting that it is applicable in crop improvement.