Efforts to engineer plant cell wall formation for enhanced biofuel production commonly target lignin biosynthesis in order to reduce lignin content and thereby improve yields of ethanol from cellulose, a complex polysaccharide important for cell wall structure. Lignin is troublesome for biofuel production because it is the main contributor to plant biomass recalcitrance due to its toughness and heterogeneity. By reducing lignin content, the cellulose is more easily accessible to the chemical and biological reagents used to break it down. Lowering the expression level of CCR in particular has emerged as a common strategy for accomplishing this goal, and this strategy has resulted in successful lignin content reduction and increased ethanol production from several plant species including tobacco (Nicotiana tabacum) and poplar (Populus tremula x Populus alba). Challenges with this strategy include the wide variation in expression levels associated with current plant genetic transformation technologies in addition to the dramatic decrease in overall growth and biomass that typically accompanies low lignin production. However, it has been shown that by targeting CCR down-regulation to specific tissue types or coupling it to down-regulation of cinnamyl alcohol dehydrogenase (CAD), the latter challenge at least can be somewhat mitigated. References EC 1.2.1 NADPH-dependent enzymes Enzymes of unknown structure