Genomic nucleotide sequence of an Arabidopsis thaliana gene encoding a cinnamyl alcohol dehydrogenase.

CAD (EC 1.1.1.195) catalyzes the conversion of cinnamaldehydes to the corresponding alcohols, the final step in the biosynthesis of the lignin precursors. CAD is considered one of the target enzymes for the modification of lignin biosynthesis (Whetten and Sederoff, 1991). This enzyme has been purified and characterized from severa1 plant species. cDNAs of CAD-encoding genes have been cloned from tobacco (Nicotiana tabacum) (Knight et al., 19921, Eucalyptus gunni i (Feuillet et al., 1993), Aralia cordata (Hibino et al., 1993), Pinus taeda (OMalley et al., 1992), Picea abies (Galliano et al., 1993), and poplar and alfalfa (Van Doorsselaere et al., 1995). Furthermore, a genomic clone has been obtained from Eucalyptus botryoides (Hibino et al., 1994). Here we report on the nucleotide sequence of the 3614-bp Arabidopsis tkaliana cad gene. The poplar cad cDNA (Van Doorsselaere et al., 1995) was used as a probe to screen a genomic library from A. tkaliana (Krebbers et al., 1988). A 5-kb HindIII fragment hybridizing with both the 5’ end and the 3‘ end of the poplar cad cDNA was isolated. This fragment was subcloned in pUC18 and sequenced. The analysis of the genomic clone revealed four introns and five exons encoding a polypeptide of 365 amino acids (Table I). The 5‘ sequenced region contains a putative TATA box and a CAT box at 126 bp and 200 bp upstream of the ATG, respectively. The cis element TAACGT, present in the anthocyanin biosynthesis genes in maize, could be identified. The calculated molecular mass of the encoded protein is 39.1 kD. The sequence identities with other CAD polypeptides were 75% ( E . gunnii), 76% (alfalfa), 67% (P. abies), 78% (poplar), 76% (tobacco), and 80% (A. cordata) at the amino acid level. Moreover, the A. tkaliana cad-coding sequence has 50% identity with the Eli3 gene from A. thaliana (Kiederowski et al., 1992). Eli3 also encodes an alcohol dehydrogenase and has a potential role in plant defense toward pathogens.