Lignocellulosic biomass is of particular interest as a plant-based feedstock to produce biofuels, biochemicals and biomaterials. However, current lignocellulosic feedstock suffers from a relatively low processing efficiency, mainly because of the presence of the recalcitrant lignin polymer. To overcome this problem, biomass crops could be engineered to reduce their lignin levels. Two elements are key for a successful lignin engineering strategy: i) a profound knowledge of genes involved in lignin biosynthesis allowing fine-tuning of the pathway and ii) an engineering strategy that avoids the biomass-yield penalty that is often observed in plants with reduced lignin levels. In this project, we will work on both key elements. The first goal of this project proposal is to deepen our knowledge of the lignin biosynthetic pathway via the elucidation of the biochemical role of ALCOHOL DEHYDROGENASE 3 (ADH3) in Arabidopsis and poplar. We identified ADH3 as a candidate to be involved in lignin biosynthesis, based on co-expression analyses. The second goal of this project proposal is to overcome the biomass-yield penalty in low-lignin plants. Therefore, we will perform a suppressor screen on cinnamoyl-CoA reductase1 (ccr1) mutants that have a reduced biomass phenotype. To explore the valorization potential, we will also investigate whether the findings of the suppressor mutation in Arabidopsis can be translated to a biomass crop, poplar.