Although the primary structure of proteins, nucleic acids, and carbohydrates can be readily determined, no sequencing method has been described yet for lignin, the second most abundant biopolymer on earth.

Lignin is made from the combinatorial radical-radical coupling of monolignols and many other less abundant monomers. This polymerization process leads to a plethora of units and linkage types that affect the physicochemical characteristics of the cell wall. Current methods to analyze the lignin structure focus only on the frequency of the major monomeric units and interunit linkage types. We have now developed a mass-spectrometry-based tool to determine the sequence of units in small lignin polymers as well as the bonds connecting these units (Morreel et al., 2010). This technique is now used to identify lignin polymers composed of as yet unknown units and bond types. This knowledge will be instrumental in engineering plants with new lignin structures that are more easily degraded during the pretreatment of plant biomass.