The sweet potato RbcS gene (IbRbcS1) promoter confers high-level and green tissue-specific expression of the GUS reporter gene in transgenic Arabidopsis

Sweet potato is an important crop because of its high yield and biomass production. We herein investigated the potential of the promoter activity of a small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RbcS) from sweet potato (Ipomoea batatas) in order to develop the high expression system of exogenous DNA in Arabidopsis. We isolated two different cDNAs (IbRbcS1 and IbRbcS2) encoding RbcS from sweet potato. Their predicted amino acid sequences were well conserved with the mature RbcS protein of other plants. The tissue-specific expression patterns of these two genes revealed that expression of IbRbcS1 was specific to green tissue, whereas that of IbRbcS2 was non-photosynthetic tissues such as roots and tubers. These results suggested that IbRbcS1 was predominantly expressed in the green tissue-specific of sweet potato over IbRbcS2. Therefore, the IbRbcS1 promoter was transformed into Arabidopsis along with β-glucuronidase (GUS) as a reporter gene. GUS staining and semi-quantitative RT-PCR showed that the IbRbcS1 promoter conferred the expression of the GUS reporter gene in green tissue-specific and light-inducible manners. Furthermore, qPCR showed that the expression levels of GUS reporter gene in IbRbcS1 pro:GUS were same as those in CaMV 35S pro:GUS plants. These results suggest that the IbRbcS1 promoter is a potentially strong foreign gene expression system for genetic transformation in plants.