|CASS, CYNTHIA - Illinois State University
|LAVELL, ANASTASIYA - University Of Minnesota
|SANTORO, NICHOLAS - Michigan State University
|FOSTER, CLIFF - Michigan State University
|KARLEN, STEVEN - University Of Wisconsin
|SMITH, REBECCA - University Of Wisconsin
|RALPH, JOHN - University Of Wisconsin
|SEDBROOK, JOHN - Illinois State University
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2016
Publication Date: 5/26/2016
Citation: Cass, C.L., Lavell, A.A., Santoro, N., Foster, C.E., Karlen, S.D., Smith, R., Ralph, J., Garvin, D.F., Sedbrook, J.C. 2016. Cell wall composition and biomass recalcitrance differences within a set of Brachypodium distachyon inbred lines. Frontiers in Plant Science. 7:708.
Interpretive Summary: There is significant interest in the use of non-petroleum renewable sources of energy, including biofuels such as ethanol produced from the fermentation of energy grass species such as switchgrass. Optimizing the yield of biofuels from energy grasses will require modifying various features of these species. The small model grass Brachypodium distachyon (Brachypodium) has been proposed as a surrogate for accelerating our understanding of what genetic and molecular modifications to energy grasses will improve biofuel yields. In this study, a set of genetically diverse genotypes of Brachypodum from various locations in Europe and Asia was used to examine the extent of genetic variation present for a series of growth habit and biochemical traits that, when altered, may increase the amount of ethanol that can be recovered from energy grasses. There was significant variation between the genotypes for plant height, the time it takes for plants to flower, and overall plant weight. Similarly, variation both for concentrations of some chemical compounds that impair efficient biofuel production was found in dried stem tissue from these experimental materials, as was variation in the amount of several sugars that can be fermented into ethanol after a number of different chemical and heat treatments. Our results suggest that Brachypodium can serve as a research test bed for evaluating specific genetic and molecular trait modifications relevant to the improvement of proposed energy grasses. Knowledge gained from such experimentation in Brachypodium, when transferred to energy grasses such as switchgrass, will lead to more rapid improvement of these species through breeding, thus making them better sources of renewable energy.
Technical Abstract: Brachypodium distachyon (Brachypodium) has emerged as a useful model system for studying traits unique to graminaceous species, owing to its amenability to laboratory experimentation and the availability of extensive genetic and germplasm resources. We assessed the extent of natural variation for traits relevant to biomass conversion to biofuels in seven genetically diverse inbred lines of Brachypodium. The inbred lines varied significantly for vernalization requirement, flowering time, and culm height and number, falling into four different groups. Senesced stems plus leaf sheaths exhibited significant differences in acetyl bromide soluble lignin (ABSL), cell wall polysaccharide-derived sugars, and hydroxycinnamates content, as well as in Syringyl:Guaiacyl (S:G) lignin ratios. Free glucose, sucrose, and starch content also differed significantly in these tissues, as did the amounts of sugars released from cell wall polysaccharides (digestibility) upon exposure to a panel of thermochemical pretreatments followed by hydrolytic enzyme digestion. Strong correlations were identified between inbred line lignin compositions and plant growth characteristics including biomass accumulation and time of spike emergence, and between relative amounts of cell wall polysaccharides as inferred by cell wall sugars content and degrees of biomass digestibility. Finally, stem biomass digestibility, cell wall p-coumarate and ferulate content, and free-sugar levels changed significantly with increased vernalization duration for some inbred lines, revealing that vernalization affects more than just flowering time and total biomass accumulation. These results show that Brachypodium displays substantial phenotypic variation for biomass-related traits directly relevant to the improvement of biomass quality and quantity, and thus can serve as a functional model for these traits in bioenergy crop grasses.