Maize is a major agricultural crop world-wide. Lignin modifications are used to improve forage digestibility and the processing efficiency of the non-edible maize biomass, i.e., leaves and stem. For instance, caffeic acid O-methyltransferase (comt) maize mutants have reduced lignin content, reduced incorporation of O-methylated monomers in the lignin and higher digestibility. However, in contrast to Arabidopsis comt mutants, maize comt mutants have substantial amounts of O-methylated lignin monomers. This proves that besides COMT, additional O-methyltransferases are active in lignin biosynthesis in maize. Here, we aim to discover and unravel the function of these OMT genes. Therefore, we will investigate the biological role of three OMT genes that we selected as highly promising candidates because of their tight co-expression with lignin biosynthetic genes in large-scale transcriptomic datasets. The function of the three OMT genes will be investigated via in vitro enzyme assays and genetic complementation of Arabidopsis comt mutants. Additionally, the corresponding maize mutants (stacked with comt) will be generated via CRISPR/Cas9 technology and characterized via state-of-the-art metabolomics, multiple-level cell-wall characterization, and biomass yield and digestibility measurements. With this project, we will gain fundamental insight into lignin biosynthesis in a grass species, potentially opening-up new roads to the development of optimized feedstock for the biorefinery.