Disrupting the cinnamyl alcohol dehydrogenase 1 gene (BdCAD1) leads to altered lignification and improved saccharification in Brachypodium distachyon

Brachypodium distachyon (Brachypodium) has been proposed as a model for grasses, but there is limited knowledge about its lignins and no data about lignin-related mutants. The cinnamyl alcohol dehydrogenase (CAD) genes involved in lignification are promising targets to improve the cellulose-to-ethanol conversion process. The down-regulation of CAD often induces a reddish coloration of lignified tissues. Based on this observation, we screened a chemically-induced population of Brachypodium mutants (Bd21-3 background) for red culm coloration. Thus, we identified two mutants Bd4179 and Bd7591, with mutations in the BdCAD1 gene. The mature stems of these mutants displayed a reduced CAD activity and a lower lignin content. Their lignins were enriched in 8-O-4 and 4-O-5 coupled sinapaldehyde units as well as in resistant interunit bonds and free phenolic groups. By contrast, there was no increase in coniferaldehyde end-groups. Moreover, sinapic acid ester-linked to cell walls was measured for the first time in a lignin-related CAD grass mutant. The functional complementation of the Bd4179 mutant with the wild-type (WT) BdCAD1 allele restored a WT phenotype and lignification. Saccharification assays revealed that Bd4179 and Bd7591 lines were more susceptible to enzymatic hydrolysis than WT plants. In this work, we have demonstrated that BdCAD1 is involved in lignification of Brachypodium. We have shown that a single nucleotide change in BdCAD1 reduces the lignin level and increases the branching degree of lignins through the incorporation of sinapaldehyde. These changes make the saccharification of alkaline-pretreated cell walls easier without compromising plant growth. © 2012 The Authors. The Plant Journal © 2012 Blackwell Publishing Ltd.