Construction vascular-specific expression bi-directional promoters in plants

Promoters that have been widely used for both basic research and biotechnological application in plants are generally unidirectional. Here we describe a strategy to bi-directionalize the vascular-specific expression grp1.8 promoter (here named GRPp) and 4CL1 promoter (here named 4CL1p) so that one promoter can direct the vascular-specific expression of two genes, one on each end of the promoter. The minimal promoter (35Smini or GRP mini), when fused at the 5′ end of the specific expression promoter (GRPp or 4CL1p) to form bi-directional promoter (35Smini-GRPp, 35Smini-4CL1p or GRPmini-GRPp), was able to direct expression of the glucuronidase (gus) and green fluorescent protein (gfp) gene in all independent transgenic tobacco lines. Stable expression of gusA and gfp genes in transgenic plants was analyzed by histochemical staining for GUS and fluorescence microscopic observation under UV for GFP in transgenic plants. The remarkable transcript levels of GFP and GUS were detected by real-time PCR in independent transgenic tobacco lines. Their vascular-specific bi-directional promoters should be used to vascular-specific expression several functional genes in transgenic plants simultaneously.