Plant Molecular Biology 27: 651-667, 1995. © 1995 Kluwer Academic Publishers. Printed in Belgium. 651 Tissue- and cell-specific expression of a cinnamyl alcohol dehydrogenase promoter in transgenic poplar plants Catherine Feuillet 1.3, Virginie Lauvergeat 1, Christine Deswarte ~, Gilles Pilate 2, Alain Boudet 1,, and Jacqueline Grima-Pettenati 1 1UniversitO Paul Sabatier, Centre de Biologie et Physiologie Vdgdtales, URA CNRS 1457, 118 route de Narbonne, 31062 Toulouse c~dex, France (* author for correspondence); 2INRA Centre d'OrlOans Ardon, 45160 Orldans, France; 3present address: Swiss Federal Research Station for Agronomy Zarich, Department of plant breeding, Reckenholzstrasse 191, 8046 Ziirich, Switzerland Received 21 September 1994; accepted in revised form 14 December 1994 Key words: eucalyptus, wood, xylem, lignin biosynthesis, cinnamyl alcohol dehydrogenase, promoter-GUS fusion Abstract Cinnamyl alcohol dehydrogenase (CAD) which catalyses the synthesis of the cinnamyl alcohols, the immediate precursors of lignins, from the corresponding cinnamaldehydes is considered to be a highly specific marker for lignification We have isolated and characterized a CAD genomic clone from euca- lyptus, a woody species of economic importance. The full-length promoter (EuCAD, 2.5 kb) and a se- ries of 5' deletions were fused to the/~-glucuronidase (GUS) reporter gene. These constructs were tested in a homologous transient expression system of eucalyptus protoplasts which enabled the identification of several regions involved in transcriptional control. In order to study the spatial and developmental regulation of the CAD gene, the chimeric gene fusion (EuCAD-GUS) was then transferred via Agrobac- terium tumefaciens-mediated transformation into poplar, an easily transformable woody angiosperm. Quantitative fluorometric assays conducted on eight independent in vitro transformants showed that GUS activity was highest in roots followed thereafter by stems and leaves. Histochemical staining for GUS activity on both in vitro primary transformants and more mature greenhouse-grown plants indi- cated a specific expression in the vascular tissues of stems, roots, petioles and leaves. At the onset of xylem differentiation, GUS activity was detected in parenchyma cells differentiating between the xylem- conducting elements. After secondary growth has occurred, GUS activity was localized in xylem ray cells and parenchyma cells surrounding the lignified phloem and sclerenchyma fibers. This first character- ization of a woody angiosperm CAD promoter provides functional evidence for the role of CAD in lignification and suggests that parenchyma cells expressing CAD may provide lignin precursors to the adjacent lignified elements (vessels and fibres). The nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X75480.