LACCASE5 Is Required for Lignification of the Brachypodium distachyon Culm

The oxidation of monolignols is a required step for lignin polymerization and deposition in cell walls. In dicots, both peroxidases and laccases are known to participate in this process. Here, we provide evidence that laccases are also involved in the lignification of Brachypodium distachyon, a model plant for temperate grasses. Transcript quantification data as well as in situ and immunolocalization experiments demonstrated that at least two laccases (LACCASE5 and LACCASE6) are present in lignifying tissues. A mutant with a misspliced LACCASE5 messenger RNA was identified in a targeting-induced local lesion in genome mutant collection. This mutant shows 10% decreased Klason lignin content and modification of the syringyl-to-guaiacyl units ratio. The amount of ferulic acid units ester linked to the mutant cell walls is increased by 40% when compared with control plants, while the amount of ferulic acid units ether linked to lignins is decreased. In addition, the mutant shows a higher saccharification efficiency. These results provide clear evidence that laccases are required for B. distachyon lignification and are promising targets to alleviate the recalcitrance of grass lignocelluloses.