Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry

Committee Chair

Natalia Dudareva

Committee Member 1

Joseph P. Ogas

Committee Member 2

Jeremy R. Lohman

Committee Member 3

Joshua R. Widhalm

Abstract

Chapter 1 of this dissertation provides background information into the two plant terpenoid biosynthetic pathways, the mevalonate (MVA) and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathways. These pathways are responsible for the formation of the five-carbon building blocks isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). These metabolites are then condensed to form various chains of C5x terpenoids. The diversity of terpenoids within the diverse Lamiaceae is also discussed.

Chapter 2 looks at the role of a homolog of the archeal gene isopentenyl phosphate kinase (IPK) in plants. IPK is found in all sequenced plant genomes and acts in parallel with the canonical MVA pathway to produce IPP and DMAPP. IPK returns the dephosphorylated metabolites isopentenyl monophosphate (IP) and dimethylallyl monophosophate (DMAP), which act as inhibitors for downstream terpenoid biosynthesis, to IPP and DMAPP.

Chapter 3 then looks at the perpetrator of dephosphorylated IPP and DMAPP by determining whether this is specific or non-specific phosphorylation. This chapter provides evidence that two members of the Nudix hydrolase family, Nudx1 and Nudx3, are responsible for this dephosphorylation. De novo biosynthesis of IP, via overexpression of the Roseiflexus castenholzii phosphomevalonate decarboxylase (MPD) suggests the importance of subcellular sequestration of terpenoid metabolites as well as the importance of phosphomevalonate kinase (PMK) on regulation of the MVA pathway.

Chapter 4 determines the evolutionary relationship of terpenoid biosynthesis in the diverse Lamiaceae, or mint, family. Mints produce substantial quantities of mono- and sesquiterpenes and also produce geranyl pyrophosphate (GPP)-derived metabolites called iridoids. After surveying the metabolite profiles and transcriptome data from 48 mint species, there is evidence of correlation between those mint species producing iridoids and iridoid biosynthetic genes. Likewise, a strong correlation was discovered between the presence/absence of iridoids and expression of geraniol synthase (GES), the enzyme responsible for the branchpoint in the production of iridoids or canonical monoterpenes.

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