Figure 6: Principle of the GAL4:GFP enhancer trap system for gene misexpression in specific cell types.
A modified GAL4 gene (GAL4-VP16) fused to a minimal promoter (MP) that responds to chromosomal enhancer elements is introduced into transgenic plants on a T-DNA vector. The T-DNA also contains a gfp gene fused to tandemly arrayed GAL4 binding sites (UAS for upstream activating sequence) . GFP reports GAL4-VP16 expression because GAL4 controls transcription of GFP through the UAS elements. Misexpression of gene X is achieved by super-transformation the UAS:geneX fusion to a line with an individual GAL4 enhancer trap insertion. GAL4 activates geneX causing it to be expressed in the same pattern as the GFP reporter. LB and RB left border and right border of the T-DNA respectively.