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Background  Cinnamoyl CoA reductase (CCR) and cinnamyl alcohol dehydrogenase (CAD) catalyze the final steps in the biosynthesis of monolignols, the monomeric units of the phenolic lignin polymers which confer rigidity, imperviousness and resistance to biodegradation to cell walls. We have previously shown that the  Eucalyptus gunnii CCR  and  CAD2  promoters direct similar expression patterns in vascular tissues suggesting that monolignol production is controlled, at least in part, by the coordinated transcriptional regulation of these two genes. Although consensus motifs for MYB transcription factors occur in most gene promoters of the whole phenylpropanoid pathway, functional evidence for their contribution to promoter activity has only been demonstrated for a few of them. Here, in the lignin-specific branch, we studied the functional role of MY B  elements as well as other  cis -elements identified in the regulatory regions of  EgCAD2  and  EgCCR  promoters, in the transcriptional activity of these gene promoters.    Results  By using promoter deletion analysis and  in vivo  footprinting, we identified an 80 bp regulatory region in the  Eucalyptus gunnii EgCAD2  promoter that contains two MYB elements, each arranged in a distinct module with newly identified  cis -elements. A directed mutagenesis approach was used to introduce block mutations in all putative  cis -elements of the  EgCAD2  promoter and in those of the 50 bp regulatory region previously delineated in the  EgCCR  promoter. We showed that the conserved MYB elements in  EgCAD2  and  EgCCR  promoters are crucial both for the formation of DNA-protein complexes in EMSA experiments and for the transcriptional activation of  EgCAD2  and  EgCCR  promoters in vascular tissues  in planta . In addition, a new regulatory  cis -element that modulates the balance between two DNA-protein complexes  in vitro  was found to be important for  EgCAD2  expression in the cambial zone.    Conclusions  Our assignment of functional roles to the identified  cis -elements clearly demonstrates the importance of MYB  cis -elements in the transcriptional regulation of two genes of the lignin-specific pathway and support the hypothesis that MYB elements serve as a common means for the coordinated regulation of genes in the entire lignin biosynthetic pathway.

Coordinated transcriptional regulation of two key genes in the lignin branch pathway - CAD and CCR - is mediated through MYB- binding sites