A reporter gene under the control of tms or aux promoters is differentially expressed in tobacco and barley protoplasts

Agrobacterium tumefaciens and some Agrobacterium rhizogenes strains possess auxin biosynthesis genes (tms and aux genes respectively), responsible for a de novo auxin biosynthetic pathway in transformed plant cells. A comparison is presented of the potential expression of these genes in a monocotyledonous (barley) and a dicotyledonous plant (tobacco). The promoters of the genes were translationally fused to the β-glucuronidase reporter gene and analysed in transient expression experiments. The tms and aux fusions were highly expressed in tobacco, but not in barley. However, the aux enhancer active in tobacco, conferred low β-glucuronidase expression in barley when fused to a truncated cauliflower mosaic virus 35S promoter. The results are discussed in relation to the differential responses to Agrobacterium infection in monocots and dicots.