Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Fall 2020

Thesis Director

Thomas Canam

Thesis Committee Member

Gary A. Bulla

Thesis Committee Member

Michael W. Beck

Abstract

Plant biomass is a renewable and sustainable feedstock for biofuel production that can reduce societal dependence on fossil fuels. However, the production of liquid biofuels from the non-starch (i.e. lignocellulosic) material through fermentation technology is limited due to the complexity of the cell wall structure. This necessitates the use of chemical, thermal, and/or mechanical pretreatment technologies, which adds significant capital, operational, and environmental costs. Biological pretreatment strategies have the potential to mitigate these expenses by harnessing the innate ability of specialized bacteria and fungi to deconstruct lignocellulose. White-rot fungi (e.g. Trametes versicolor) have been shown to be effective at biological pretreatment of lignocellulose, yet the biochemical mechanisms associated with cell wall degradation require further study. For example, it was uncertain if these fungi have a homogenous response to various feedstocks or are able to sense subtle changes in cell wall chemistry. The present study examined the transcriptome response by Trametes versicolor to transgenic hybrid poplar (Populus tremula × alba) lines with altered syringyl (S) and guaiacyl (G) lignin. Specifically, the transcriptional response of the fungus to wild-type wood was compared to that from the wood of six transgenic lines with three lignin phenotypes: LSX (low S with hydroxy G), LSHG (low S with high G), and HS (high S). The transcriptome of T. versicolor varied according to the lignin phenotype of the wood, with the LSX wood resulting in the most substantial changes in T. versicolor transcript abundance, presumably due to the presence of hydroxy G lignin. For example, the transcripts for several lignin peroxidases (LiP3, LiP4, LiP10, and LiP12) were highly downregulated by the fungus on LSX wood compared to wild-type wood. Overall, the results of this study demonstrated that T. versicolor was able to respond to changes in lignin chemistry among wood with the same genetic background, which has important implications for biological pretreatment strategies involving feedstocks that are genetically modified or have natural variations in cell wall chemistry.

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