Altered lignin biosynthesis improves cellulosic bioethanol production in transgenic maize plants down-regulated for cinnamyl alcohol dehydrogenase
Cinnamyl alcohol dehydrogenase (CAD) is a key enzyme involved in the last step of monolignol biosynthesis. The effect of CAD down-regulation on lignin production was investigated through a transgenic approach in maize. Transgenic CAD-RNAi plants show a different degree of enzymatic reduction depending on the analyzed tissue and show alterations in cell wall composition. Cell walls of CAD-RNAi stems contain a lignin polymer with a slight reduction in the S-to-G ratio without affecting the total lignin content. In addition, these cell walls accumulate higher levels of cellulose and arabinoxylans. In contrast, cell walls of CAD-RNAi midribs present a reduction in the total lignin content and of cell wall polysaccharides. In vitro degradability assays showed that, although to a different extent, the changes induced by the repression of CAD activity produced midribs and stems more degradable than wild-type plants. CAD-RNAi plants grown in the field presented a wild-type phenotype and produced higher amounts of dry biomass. Cellulosic bioethanol assays revealed that CAD-RNAi biomass produced higher levels of ethanol compared to wild-type, making CAD a good target to improve both the nutritional and energetic values of maize lignocellulosic biomass. ; This work was supported by the Spanish 'Ministerio de Ciencia e Innovación' (AGL2008–05157), the European Community ('COPOL' project: integrated control of polysaccharide and lignin biosynthesis to improve cellulose content and availability and fibre quality, QLK5-CT-2000–01493), and the CONSOLIDER-INGENIO program (CSD2007–00036). S.F. was financed by an I3P contract from the 'Consejo Superior de Investigaciones Científicas'. D.C.-R. was initially financed by the Spanish 'Ministerio de Educación y Ciencia' ('Ramón y Cajal' Program). A.E. was financed by DGICYT (CGL2008–02470BOS) and Junta de Castilla y León (LE004A10-2). This work was carried out within the framework of the 'Xarxa de Referència de Biotecnologia' (XarBa) from the Autonomous Government of Catalonia. ; Peer reviewed