Suchergebnisse

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

Coumarate 3-hydroxylase (C3H) catalyzes a key step of the synthesis of the two main lignin subunits, guaiacyl (G) and syringyl (S) in dicotyledonous species. As no functional data are available in regards to this enzyme in monocotyledonous species, we generated C3H1 knock-down maize plants. The results obtained indicate that C3H1 participates in lignin biosynthesis as its down-regulation redirects the phenylpropanoid flux: as a result, increased amounts of p-hydroxyphenyl (H) units, lignin-associated ferulates and the flavone tricin were detected in transgenic stems cell walls. Altogether, these changes make stem cell walls more degradable in the most C3H1-repressed plants, despite their unaltered polysaccharide content. The increase in H monomers is moderate compared to C3H deficient Arabidopsis and alfalfa plants. This could be due to the existence of a second maize C3H protein (C3H2) that can compensate the reduced levels of C3H1 in these C3H1-RNAi maize plants. The reduced expression of C3H1 alters the macroscopic phenotype of the plants, whose growth is inhibited proportionally to the extent of C3H1 repression. Finally, the down-regulation of C3H1 also increases the synthesis of flavonoids, leading to the accumulation of anthocyanins in transgenic leaves. ; Funding: This work was supported by the Spanish "Ministerio de Economía y Competitividad" [AGL2011-30545-C02-01 to D.C.-R., AGL2011-30545-C02-02 to A.E., and AGL2011-25379 (co-financed by FEDER funds) to J.C.R.] and received financial support from the CONSOLIDER-INGENIO program [CSD2007-00036] from the Spanish Ministerio de Ciencia e Innovación. This work was carried out within the framework of the "Xarxa de Referència de Biotecnologia" (XarBa) from the Autonomous Government of Catalonia. R.S. was financed by the postdoctoral contracts "Isidro Parga Pondal" supported by the Autonomous Government of Galicia and the European Social Fund and "Ramón y Cajal", supported by the Spanish Ministry of Economy and Competitiveness and the University of Vigo. J.R. thanks CSIC for a JAE-DOC contract of the program "Junta para la Ampliación de Estudios" co-financed by the European Social Fund. ; Peer Reviewed