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Graduation Term

2018

Degree Name

Master of Science (MS)

Department

School of Biological Sciences

Committee Chair

John C. Sedbrook

Abstract

Lignocellulosic biomass from grasses is an attractive feedstock for conversion to liquid biofuels. Much of the biomass comes from thickened secondary cell walls composed of the polysaccharides cellulose and hemicelluloses, the latter cross-linked to and embedded within the heterogeneous phenolic polymer lignin. While lignin is required for plant rigidity, water transport, and defense, lignin also contributes to the recalcitrance of lignocellulosic biomass to deconstruction and conversion to second generation liquid biofuels. One path toward altering the recalcitrance of lignin is to mis-regulate genes in pathways that are involved in the incorporation of fermentation inhibitors such as acetate or p-Coumaric acid (pCA). Here we explore the function of BAHD acyltransferases with homology to p-COUMAROYL-COA MONOLIGNOL TRANSFERASE (PMT). Since PMT function results in pCA-monolignol conjugate incorporation into the growing cell wall lignin polymer, we are manipulating closely related BAHD acyltransferases with the goal of identifying novel cell-wall-modifying enzymes that can be manipulated to improve plant biomass properties. Previously, our lab conducted RNA Sequencing (RNASeq) analysis on plants with mis-regulated BdPMT. From that analysis, we identified two putative acyltransferases that were positively co-regulated with BdPMT mis-expression, namely, BdPMT-like-1 (BdPML-1) and BdPMT-like-2 (BdPML-2). In multiple transgenic lines, strong overexpression of BdPML-2 resulted in stunted plants with cell walls that had significantly less p-Coumaroyl- and Feruloyl-Arabinose (CA-ARA and FA-ARA) released from hemicellulose compared to wild type (WT). We determined that the stunted phenotype was likely due to a secondary insertion site effect, rather than to the overexpression of BdPML-2, by outcrossing stunted plants and restoring WT growth habit. Overexpression of BdPML-1 resulted in cell walls having significantly higher γ-acetate on lignin polymers. Besides these data, this thesis will summarize progress we are making in characterizing BdPML-1 and BdPML-2 knockdown lines along with our hypotheses related to the function of these genes.

Access Type

Thesis-ISU Access Only

DOI

http://doi.org/10.30707/ETD2018.Telander.T

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