High lignin content correlates with the recalcitrance of biomass to enzymatic saccharification during biofuel production and with reduced in-rumen digestibility of forages. As a result of many years work on the biosynthesis of lignin and its genetic controls in both the crop alfalfa (Medicago sativa) and the model plant Medicago truncatula, collaboration with a commercial partner has resulted in the release of low lignin alfalfa with superior forage quality and management characteristics. However, economic considerations support valorization, rather than removal, of lignin for biorefining. To this end, we have been working on the biosynthesis and engineering of novel lignins, such a C-lignin, with favorable properties for conversion to bioproducts, and these studies are revealing new twists to the previously accepted pathways for synthesis of lignin. Proanthocyanidins (PAs, also known as condensed tannins) are the second most abundant plant polyphenolic compounds after lignin, and exhibit a range of protective, health-promoting and organoleptic properties. We are working to introduce them into alfalfa to improve nutrition and prevent pasture bloat in ruminant animals. It is possible to engineer PAs in tissues that do not naturally accumulate them through ectopic expression of transcription factors. This approach does not, however, allow for the fine-tuning of PA structure in terms of chain length and monomer composition (i.e. the nature of the starter and extension units). Through analysis of transposon insertion mutants in M. truncatula, we have now shown that some enzymes of the accepted PA pathway have new functions that allow for control of PA chain length and composition. These observations will enable us to produce “designer” PAs for examination of PA structure-activity relationships in relation to forage quality and other properties.

Graduate Students: Please join Dr. Dixon for lunch and discussion following the seminar in N-120 Turner Hall. R.S.V.P. to pasarver@illinois.edu.