New Type of Lignin Discovered in Vanilla Plant
Found within the plant cell wall, lignin is a complex polymeric compound that provides the plant with both mechanical support and protection from pests and pathogens. However, the structural rigidity of this compound also inhibits efficient conversion of the sugars within plant cell walls into biofuels, making lignin a major obstacle to the efficient production of biofuels from cellulosic feedstocks. Three types of lignin are usually found in nature: H-, G-, and S-lignins. They are synthesized by polymerization of their respective monolignol units. However, lignin biosynthesis can be relatively flexible, sometimes allowing different and more unusual monolignols to be incorporated. Researchers at the DOE BioEnergy Science Center (BESC) and DOE Great Lakes Bioenergy Research Center (GLBRC) report the identification and characterization of a new type of polymer, C-lignin, composed almost exclusively of caffeyl units. Detected in the Vanilla orchid, a few related orchids, and some cactus species, this unique new lignin was found only in the seed coats, with more conventional lignins observed in other plant tissues. These results may lead to a greater understanding of the lignin biosynthetic pathway, as well as new approaches for engineering biomass that can be more easily and efficiently digested for conversion into biofuels.
Chen, F., Y. Tobimatsu, D. Havkin-Frenkeld, R. A. Dixon, and J. Ralph. 2012. “A Polymer of Caffeyl Alcohol in Plant Seeds,” Proceedings of the National Academy of Sciences of the United States of America 109(5), 1772-77. DOI: 10.1073/pnas.1120992109.