Analysis of the Agrobacterium tumefaciens pTiChry5 6b promoter

The 6b gene of Agrobacterium tumefaciens has evolved to become transcriptionally active in plant cells and has been postulated to modify the activity of plant growth regulators, auxins and cytokinins. To delimit the region that is necessary for expression and is responsible for auxin inducibility, we have constructed a series of 5′ deletions and duplications of the A. tumefaciens strain Chry5 6b gene promoter. These deletions and duplications of the 6b gene promoter were fused to the GUS reporter gene and transformed into tobacco (Nicotiana tabacum L cv KY160) to monitor levels and tissue specificity of expression. The −284 bp region upstream of 6b gene translational start site was enough for basal expression and was inducible by auxins, 2,4-D and NAA and to a lesser extent by cytokinin. However, the −438 bp fragment showed higher auxin inducibility. The auxin inducibility was increased by duplication of the upstream region fragments of the promoter. GUS expression was mostly confined to the vascular tissue and the meristem region.