Lignin Modification to Improve Sorghum for Bioenergy Uses, and Impacts of These Modifications on Plant-Biotic Interactions

Modifying lignin content and composition are major targets for bioenergy feedstock improvement. Our goals are to improve sorghum biomass for both biochemical and thermal bioenergy conversion by developing experimental lines that have altered lignin content and composition beyond normal levels, and to understand how these changes impact conversion technologies and plant fitness. To reduce lignin content and alter lignin composition, brown midrib (bmr) mutants, generated through chemical mutagenesis, are being utilized. bmr6 and 12 sorghum lines have been shown to significantly increase ethanol conversion through saccharification and fermentation. To increase lignin content for thermal bioenergy conversion, a series of transgenic lines overexpressing phenylpropanoid biosynthetic genes and a pathway regulatory gene have been developed. In addition to the prominence of lignin as a target for bioenergy feedstock improvement, lignin has also been implicated as playing a critical role in plant defense responses against both pathogens and insect pests. Thus, we are examining whether the lignin-modified lines being developed have altered responses to key sorghum insect pests (greenbugs, Schizaphis graminum; fall armyworms, Spodoptera frugiperda and corn earworms, Helicoverpa zea) and fungal pathogens (anthracnose, Colletotrichum sublineolum; charcoal rot, Macrophomina phaseolina and stalk rot, Fusarium thapsinum).  To date, none of the lignin-modified lines have shown significantly increased susceptibility to the pests and pathogens tested. In contrast, bmr6 and bmr12 plants have shown significantly increased resistance to the pest or pathogen in some interactions.