The vascular expression pattern directed by the Eucalyptus gunnii cinnamyl alcohol dehydrogenase EgCAD2 promoter is conserved among woody and herbaceous plant species

Cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195) catalyses the last step in the synthesis of the monomeric precursors of lignin. Here, we demonstrate that the vascular expression pattern conferred by the Eucalyptus gunnii EgCAD2 promoter in transgenic poplar (Populus tremula x Populus alba) is conserved in another perennial woody angiosperm of economic interest (Vitis vinifera L.), as well as in a model herbaceous plant (Nicotiana tabacum L.). Furthermore, promoter deletion analysis performed in both tobacco and poplar allowed us to identify the proximal region [-340/-124] as essential for vascular cambium/xylem-specific expression whereas the [-124/+117] region was shown to contain cis element-driving activity in phloem fibres. Interestingly, the [-340/-124] fragment contains an AC-rich cis-acting element present in numerous genes of the phenylpropanoid pathway expressed in xylem tissues, and known as a consensus Myb transcription factor binding site, suggesting that common Myb sites may provide a mechanism by which different steps of phenylpropanoid metabolism are coordinately regulated and expressed in vascular tissues. We have also shown in both tobacco and poplar that the EgCAD2 promoter is inducible by wounding and the cis-elements responsible for wounding responsiveness are located in the distal promoter region. Taken together, our data suggest that the mechanisms controlling developmental and wounding inducible expression of the EgCAD2 promoter are conserved among perennial woody and annual herbaceous plant species enabling us now to investigate in depth the transcriptional regulation of the EgCAD2 promoter in tobacco.