Comparative Transcriptome Analysis of Populus Stems to Identify Cell-wall Proteins Differentially Regulated by Corngrass1
Adam H. Lorch and Rick Meilan
Department of Forestry and Natural Resources
Feedstock from poplars (Populus spp.) can be used to produce fuels with a reduced carbon footprint. Expanded use of woody biomass as a feedstock for biofuel production would be promoted by greater conversion efficiencies. One factor affecting the recovery of carbohydrates from Populus is the recalcitrance of lignin present in the secondary cell wall.
Previous work has demonstrated that constitutive over-expression of the corn (Zea mays) tandem microRNA Corngrass1 (Cg1) in hybrid aspen (INRA 717-1B4; Populus tremula x P. alba) resulted in plants with an altered lignin content and a decreased ratio of syringyl to guaiacyl (S:G) (Rubinelli et al., 2013). I hypothesize that Cg1-based regulation of transcription factors involved in processes specifying cell fate may contribute to this lower S:G ratio, and potentially improved cell-wall degradability.
Cross-sections from four-month-old stems treated with a lignin-specific stain showed differences in cell morphology in Cg1-over-expressing (35S::Cg1) lines, as compared to the wild type. Transcriptional profiling of stem cross-sections taken from wild-type and 35S::Cg1 ramets of the same age showed differential expression of cell wall-related transcripts. For example, levels of a pectin methylesterase transcript were found to be significantly upregulated in 35S::Cg1 lines.
Production of transgenic lines incorporating RNA interference vectors targeting two Cg1-regulated genes will allow us to mimic the microRNA’s regulatory effect on these specific genes, without off-target effects on other Cg1-regulated genes. Ultimately, the engineering of a cellulosic feedstock with greater conversion efficiency will yield significant cost savings and improve Populus’ value as a bioenergy crop.