Abstract
A novel sequence that functions as a promoter element for moderate constitutive expression of transgenes, designated as the PtMCP promoter, was isolated from the woody perennial Populus tomentosa. The PtMCP promoter was fused to the GUS reporter gene to characterize its expression pattern in different species. In stable Arabidopsis transformants, transcripts of the GUS reporter gene could be detected by RT-PCR in the root, stem, leaf, flower and silique. Further histochemical and fluorometric GUS activity assays demonstrated that the promoter could direct transgene expression in all tissues and organs, including roots, stems, rosette leaves, cauline leaves and flowers of seedlings and maturing plants. Its constitutive expression pattern was similar to that of the CaMV35S promoter, but the level of GUS activity was significantly lower than in CaMV35S promoter::GUS plants. We also characterized the promoter through transient expression in transgenic tobacco and observed similar expression patterns. Histochemical GUS staining and quantitative analysis detected GUS activity in all tissues and organs of tobacco, including roots, stems, leaves, flower buds and flowers, but GUS activity in PtMCP promoter::GUS plants was significantly lower than in CaMV35S promoter::GUS plants. Our results suggested that the PtMCP promoter from poplar is a constitutive promoter with moderate activity and that its function is presumably conserved in different species. Therefore, the PtMCP promoter may provide a practical choice to direct moderate level constitutive expression of transgenes and could be a valuable new tool in plant genetic engineering.
Highlights
Constitutive promoters direct expression in most or all tissues irrespective of environmental or developmental factors
To look for putative cis-acting elements related to promoter function, the fragment was analyzed using the PLACE [71,72] and PlantCARE [73] databases
Quantitative measurement of GUS activity showed that GUS activity in the PtMCP promoter::GUS plants (T2, T4, T7, T8, T9 and T11) was significantly lower than in the CaMV35S promoter::GUS plants (Figure 4I). These results indicated that the PtMCP promoter was constitutive, but its expression intensity was significantly lower than the staining of transgenic lines (T2 and T7) containing the PtMCP promoter::GUS construct in Arabidopsis seedlings (A–D) and maturing plants (E–H)
Summary
Constitutive promoters direct expression in most or all tissues irrespective of environmental or developmental factors. Constitutive promoters are frequently introduced into basic vectors for plant transformation to promote the expression of transgenes throughout the whole plant for many purposes, such as enhancing disease resistance [27,28], abiotic stresses tolerance [29,30] and herbicide and antibiotic resistance [31] and play an important role in vaccines [32]. To achieve these certain traits, it is essential to use a strong constitutive promoter that can drive high level expression of foreign genes in most tissues
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