<p>The phenylpropanoid pathway gives
rise to a wide variety of specialized metabolites, but the majority of carbon
flux going through this pathway is directed towards the synthesis of the lignin
monomers: <i>p</i>-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol.
Lignin is a major impediment in biomass saccharification, which negatively
affects animal feed and biofuel production. In an effort to improve biomass for
the latter purposes, researchers have altered the polymer through genetic
manipulations and generated biomass with lower recalcitrance to
saccharification; however, in many cases these efforts have resulted in plant
dwarfism. To date, we do not have a full understanding of the extent of lignin
modifications a plant is able to tolerate without affecting its growth. More
importantly, the mechanism that links dwarfism and modifications in lignin
content and composition remains unknown. To contribute to answering these
questions, we designed a strategy to incorporate a novel monomer into the lignin
of <i>Arabidopsis thaliana</i>. We used mutants in genes that code for enzymes
and regulators of the phenylpropanoid pathway to redirect the pathway’s flux
towards the synthesis of <i>p</i>-coumaraldehyde and prevent the incorporation
of <i>p-</i>coumaryl alcohol. Despite being mutated for the genes typically
considered to be required for monolignol biosynthesis, the plants we generated
continue to incorporate <i>p-</i>coumaryl alcohol into their lignin. This
result suggests that the pathway’s architecture has not been completely
elucidated and that there are more enzymes involved in lignification than
previously thought. Additionally, we explored the connection between
perturbations in phenylpropanoid metabolism and plant growth, by using an
inducible system to track the changes in gene expression and metabolism that
occur when phenylpropanoid metabolism is restored in a lignin biosynthetic
mutant. The use of an inducible system allowed us to not only determine the
metabolic processes affected in this mutant, but the proximal sequence of events
that lead to restored growth when a functional copy of the mutant gene is
induced. Finally, we redirected the flux through the pathway to assess the
effects of simultaneously modulating lignin content and composition. Through
this project we discovered that redirecting phenylpropanoid flux towards the
synthesis of sinapyl alcohol in lignin-deficient mutant backgrounds, results in
plant dwarfism. The growth impairment of these mutants can be overcome by
providing exogenous coniferyl alcohol, suggesting that dwarfism in these
mutants is caused by deficiency in coniferyl alcohol and/or derivatives thereof
and not lignin alone. Altogether these projects allowed us to define the
cellular processes affected by perturbations in phenylpropanoid homeostasis and
the role of other phenylpropanoids besides lignin in this process.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13100051 |
| Date | 16 December 2020 |
| Creators | Fabiola Muro Villanueva (9525857) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Re-routing_the_phenylpropanoid_pathway_and_its_implications_on_plant_growth/13100051 |
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