Developmental Control of Lignification in Stems of Lowland Switchgrass Variety Alamo and the Effects on Saccharification Efficiency

Abstract

The switchgrass variety Alamo has been chosen for genome sequencing, genetic breeding, and genetic engineering by the US Department of Energy Joint Genome Institute (JGI) and the US Department of Energy BioEnergy Science Center. Lignin has been considered as a major obstacle for cellulosic biofuel production from switchgrass biomass. The purpose of this study was to provide baseline information on cell wall development in different parts of developing internodes of tillers of switchgrass cultivar Alamo and evaluate the effect of cell wall properties on biomass saccharification. Cell wall structure, soluble and wall-bound phenolics, and lignin content were analyzed from the top, middle, and bottom parts of internodes at different developmental stages using ultraviolet autofluorescence microscopy, histological staining methods, and high-performance liquid chromatography (HPLC). The examination of different parts of the developing internodes revealed differences in the stem structure during development, in the levels of free and well-bound phenolic compounds and lignin content, and in lignin pathwayrelated gene expression, indicating that the monolignol biosynthetic pathway in switchgrass is under complex spatial and temporal control. Our data clearly show that there was a strong negative correlation between overall lignin content and biomass saccharification efficiency. The ester-linked p-CA/FA ratio showed a positive correlation with lignin content and a negative correlation with sugar release. Our data provide baseline information to facilitate genetic modification of switchgrass recalcitrance traits for biofuel production.

Characterization of the Rust Fungus, Puccinia emaculata, and Evaluation of Genetic Variability for Rust Resistance in Switchgrass Populations

“…Switchgrass seedlings were grown in 36 celled (9×4) plastic trays, and the cultivars were arranged in a randomized block design. Five-week-old seedlings at E2 growth stage [27] were sprayed with rust urediniospores as described above, and disease symptoms on fully expanded leaves were scored at 14 days pi.…”

Structural Characterization of Lignin in Wild-Type versus COMT Down-Regulated Switchgrass

“…The transgenics were grown in the greenhouse at 26°C with 16 h light (390 µE/m 2 s). The vegetative development of switchgrass was divided into four elongation stages (E1, E2, E3, and E4) according to the criteria described by Moore et al (1991) and Shen et al (2009). Under the greenhouse conditions, switchgrass produced four visible internodes from basal to top before entering into reproductive development.…”

The Pattern of Lignin Deposition in The Cell Walls of Internodes During Barley (Hordeum vulgare L.) Development

“…Moreover, lignin deposition in cultivar Astor was most evident at the grain filling stage in all three internodes in both directions, tangential and radial. Shen et al (2009) andSarath et al (2007) noticed that in switchgrass lignification increased at the stem elongation and reproductive stages in the cell walls of older internodes. Similar lignification pattern results were also observed in maize (Jung, 2003;Jung and Casler, 2006) and in tall fescue (Chen et al, 2002).…”