Date of Award

5-11-2025

Date Published

June 2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Heather Coleman

Keywords

cell wall;genetics;glucomannan;hemicellulose;mannose;xylan

Subject Categories

Biochemistry, Biophysics, and Structural Biology | Life Sciences | Molecular Biology

Abstract

Lignocellulosic biomass as an input for biofuel generation has gained popularity in recent decades due to attainable feedstock ubiquity and an anatomical propensity to fix and sequester carbon. A major challenge facing the integration of such feedstocks is the presence of recalcitrant polymers that are extant in their cell walls, namely lignin and various hemicellulose species. Many studies have illustrated methods in which cell wall modification through genetic means has produced phenotypic improvements with regard to biomaterial generation, though to this point, none have overexpressed exogenous hemicellulose genes to shift the composition of the Populus tremula × alba cell walls. If this were to be performed, a hemicellulose sugar profile more akin to cellulose would be possible, limiting pitfalls in biomaterial production due to more uniformity in cell wall biochemistry. The present study independently expresses Pinus taeda GDP-mannose pyrophosphorylase 2 (PtGMP2) and phosphomannose isomerase (PtPMI) in the Populus tremula × alba 717 INRA-B4 hybrid poplar species. Both genes are associated with glucomannan production, a hemicellulose composed of six-carbon sugars, in contrast to the dominant xylan, composed of five-carbon sugars. Several GMP2 lines experienced greater change in height relative to the wild type, and a single line experienced an increase in mannose, a constituent of glucomannan. Such beneficial phenotypes suggest this modification has potential for integration into biomaterial feedstocks.The following describes the process by which individuals with such phenotypes were achieved, beginning with an extensive analysis on the nature of the plant cell wall along with the knowledge gaps that drove the conceptualization of this project. Following an introduction, the second chapter discusses the nature of functional diversification in the plant cell wall,characterizing the numerous families with diverse members responsible for its construction. Chapter 3 then focuses on the aforementioned study, uncovering physiological responses to the overexpression of the genes of interest and nutrient stress. Prior to beginning the project described in Chapter 3, significant time was spent characterizing the nature of functional duplicates associated with the biosynthesis and maintenance of the Populus cell wall, namely members of the Korrigan and Cobra families. Chapter 4 discusses the progression and necessary shift away from this project. A conclusion is present that discusses the nature by which findings and overall intellectual merit fit with the field of plant biotechnology, along with future directions of pursuit.

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