Molecular cloning of cDNAs coding for three sugarcane enzymes involved in lignification

Full-length cDNAs encoding the monolignol biosynthetic enzymes caffeic acid 3-O-methyltransferase (COMT, EC 2.1.1.6), cinnamoyl-CoA reductase (CCR, EC 1.2.1.44) and cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) were cloned from sugarcane (Saccharum officinarum L.). The encoded proteins (39.6, 40.1 and 38.7 kDa for COMT, CCR and CAD, respectively) were identified based on their sequence identities with the corresponding enzymes from other plant species. Pairwise comparisons of deduced amino acid sequences with known plant lignification proteins allowed the identification of important conserved domains and specific functional motifs within these enzymes. Two new conserved domains, probably involved in substrate specificity, are described for COMTs. Phylogenetic analysis showed a very close evolutionary relationship between sugarcane and maize sequences. Southern blot analyses are consistent with the presence of at least two copies of each studied gene in sugarcane genome. The comt, ccr and cad transcripts appear to happen in a parallel way in different sugarcane tissues. The mRNA accumulation patterns suggest a transcriptional regulation of these genes dependent on their specific role in lignin synthesis. The cloning and characterisation of sugarcane genes involved in lignification opens up the possibility of producing plants with lower and/or modified lignin by genetic engineering means.