Characterization and activity enhancement of the phloem-specific pumpkin PP2 gene promoter

The promoter of the pumpkin (Cucurbita moschata) PP2 gene (designated NP) was isolated from the restriction enzyme-digested genomic DNA pool by genome walking and its activity and phloem specificity were examined in transgenic tobacco plants by using GUS as a reporter. Deletion analysis of the promoter revealed that the 473-bp fragment (-465 to + 8 relative to the transcription start site; designated as NPII) exhibited similar activity as the full-length NP promoter and retained its phloem specificity. Furthermore, the sequence from -465 to -171 was shown to contain positive regulatory cis-elements for the promoter activity. An enhanced NP promoter was constructed by duplicating the sequence -465 to -85, and its activity in phloem tissue was shown to be higher than that of the Commelina Yellow Mottle Virus (CoYMV) promoter or a chimeric promoter consisting of the double enhancer sequence from the Cauliflower Mosaic Virus (CaMV) 35S promoter fused upstream to the NPII fragment.