Location: Wheat, Sorghum and Forage ResearchTitle: Genetic variation among sorghum and Brachypodium distachyon accessions for biological conversion efficiency Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/25/2011
Publication Date: 4/11/2011
Citation: Lee, S.J., Warnick, T.A., Young, N.F., Pedersen, J.F., Leschine, S.B., Hazen, S.P. 2011. Genetic variation among sorghum and Brachypodium distachyon accessions for biological conversion efficiency. Meeting Abstract presented at 2011 Genomic Sciences Contractor - Grantee Meeting/USDA-DOE Plant Feedstock Genomics for Bioenergy Awardees, Crystal City, MD, April 10-13. Published online at https://www.orau.gov/gtl2011/abstracts/hazen_samuel02.pdf Interpretive Summary:
Technical Abstract: Using the well-developed microbial system, Clostridium phytofermentans, we developed an assay that provides the ability to measure the impact of pretreatment, conversion processes, and microbial and plant genetic diversity of digestibility, and thereby determine the potential effects of numerous variables in biofuel production. In contrast to other established methods, the C. phytofermentans bioassay provides a direct and quantitative means of assessing feedstock quality, both in terms of digestibility and conversion. Moreover, the use of C. phytofermentans takes into consideration specific organismal interactions, which will certainly be critical in single stage fermentation or consolidated bioprocessing. As a baseline for the bioassay, we used two well characterized lignin mutants of Sorghum bicolor, brown midrib-6 (bmr-6) and brown midrib-12 (bmr-12) and the double mutant (bmr-6/bmr-12). Lignin, a component of secondary cell walls, is strongly associated with plant tissue recalcitrance to conversion to biofuels. These mutants exhibit a significant reduction in total lignin content and had previously been shown to be a more digestible animal feedstock. The supernatant of three day old anaerobic cultures of sorghum and C. phytofermentans was sampled and assayed for ethanol concentration. The bmr mutants yielded significantly more ethanol relative to wild type. Next, we sieved ground biomass samples and assayed only plant material ranging from 53 to 62.4 microns in size to find a similar result. Therefore, genetic differences in ethanol yield were not the result differential grinding among genotypes. In order test potential application of the assay to quantitative genetic studies and applied plant breeding of energy crops, we went on to characterize a collection of 16 field grown sorghum landraces. The sorghum accession most amenable to conversion yielded 30% more ethanol than the most recalcitrant, a range we observed among B. distachyon and Arabidopsis thaliana accessions as well. The genetic differences measured among accessions within several species are similar to the range measured between the bmr lignin mutants and wild-type sorghum. While mutations effecting lignin have a deleterious effect on plant architecture, vigor, and yield in many crop species, the accessions we observed significant variation for ethanol yield exhibit no such differences in overall plant architecture. This suggests that gain from selection and transgenic modification for feedstock quality need not be pleiotropic for low biomass yield.