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Abstract
Phylloquinone (vitamin K1) is best known for its role in chloroplasts as an electron carrier across the thylakoid membrane. However, evidence for a non-canonical plasma membrane (PM)-localized phylloquinone biosynthetic pathway has recently been reported. The two late biosynthetic pathway enzymes, MenA and MenG, lack N-terminal chloroplast-targeting sequences. The predicted PM-isoforms were proposed to function in PM electron transport in a non-photosynthetic holoparasite Phelipanche aegyptiaca. Similar PM pathway genes are found in several photosynthetic plant species belonging to the Lamiales order. One such example is the traditional Chinese herb Rehmannia glutinosa which is phylogenetically closely related to parasitic species of the Orobanchaceae family. The proposed PM phylloquinone pathway is hypothesized to be involved in the oxidative response of roots in both holoparasitic and non-parasitic plants. In order to test the hypothesis, my dissertation research was designed to 1) examine PM localization of the P. aegyptiaca MenA2 and MenG2 isoforms by confocal microscopy of GFP fusions, 2) determine MenA2 membrane topology and MenG2 enzymatic function using Escherichia coli, 3) analyze expression of the PM phylloquinone pathway genes in R. glutinosa, and 4) generate CRISPR/Cas9 knock-outs of the terminal biosynthetic genes in R. glutinosa plants for future research. The results from this research offer insight into PM-localized phylloquinone function in plant redox regulation. Future mechanistic investigation into the role of PM phylloquinone in parasitic and non-parasitic plants during growth and stress responses may contribute to the control of noxious weeds that devastate agriculture.