Phloem specific expression driven by wheat dwarf geminivirus V-sense promoter in transgenic dicotyledonous species.

Wheat dwarf geminivirus (WDV) is a single-stranded DNA Mastrevirus. The large intergenic region (LIR) of WDV contains cis-acting elements essential for the replication of the genome as well as for the bidirectional transcription of virus genes. The LIR was fused to the GUS (uidA) reporter gene and the WDV viral sense (V-sense) promoter activity derived from the stable integration of that promoter was analysed in transgenic dicot plants. Various dicot species were tested, including Nicotiana tabacum, Nicotiana benthamiana, Arabidopsis thaliana and Cucumis melo. The GUS activity driven by the WDV promoter was also compared to that obtained in plants transformed with the GUS gene controlled by the CaMV 35S promoter as well as two phloem-specific promoters derived from the Arabidopsis thaliana AtSUC2 and AtAHA3 genes. Histochemistry showed that the WDV V-sense promoter consistently induced an expression pattern restricted to the vascular tissues, predominantly in the phloem of all organs. This promoter exhibited levels of GUS activity comparable to that driven by AtSUC2 and AtAHA3 promoters. A vascular expression pattern was observed in the four dicots tested. This was stable during plant development and was not altered following viral infection by an unrelated geminivirus. The uses of such a promoter are discussed regarding the targeting to the phloem of molecules active against vascular pests or pathogens.