New Gene Discovery Clarifies Lignin Biosynthetic Pathway


Lignin is integral to plant cell wall strength and function. It is also important in bioprocessing of plant biomass, because it inhibits deconstruction of plant cell wall sugar polymers such as cellulose and hemicellulose into sugar monomers—a key step in the production of biofuels. Lignin’s irregular polymeric structure has made it difficult to establish a clear biosynthetic pathway for its formation, making it a challenging target for genetic engineering of plants for enhanced bioprocessing of plant biomass. Recently, scientists at the U.S. Department of Energy’s Great Lakes Bioenergy Research Center (GLBRC) identified a new enzyme in the biosynthetic pathway of lignin monomers. The enzyme caffeoyl shikimate esterase (CSE) was found to catalyze a previously unidentified step in the biosynthesis of lignin monomers. Analysis of plant lines with a mutation in CSE demonstrated altered accumulation of lignin precursors consistent with its hypothesized activity and position in the lignin biosynthetic pathway. This enzymatic step is important, leading to a lignin that is less inhibitory to deconstruction than wild type lignin. In fact, one CSE mutant showed significantly more saccharification (78%) than wild type (18%), though plant growth was stunted. The discovery of this previously unknown enzymatic step highlights the success of genomics, global gene expression studies, data sharing, and bioinformatics, because the gene was found by searching publicly available gene expression databases for genes of unknown function that are co-expressed with other known lignin biosynthesis genes. This more complete knowledge of the lignin biosynthesis pathway will enable more intelligent engineering of lignin biosynthesis that may lead to more efficient bioprocessing without negatively impacting plant growth and viability. The GLBRC research was carried out in collaboration with an international team of scientists from Belgium and the United Kingdom.


Vanholme, R., I. Cesarino, K. Rataj, Y. Xiao, L. Sundin, G. Goeminne, H. Kim, J. Cross, K. Morreel, P. Araujo, L. Welsh, J. Haustraete, C. McClellan, B. Vanholme, J. Ralph, G. G. Simpson, C. Halpin, and W. Boerjan. 2013. “Caffeoyl Shikimate Esterase (CSE) is an Enzyme in the Lignin Biosynthetic Pathway,” Science 341, 1103–06. DOI: 10.1126/science.1241602.