Phylloquinone Biosynthesis in Plants: Enzyme Discovery and Pathway Flux Control

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Scientific merit: Phylloquinone (vitamin K1) is a fat-soluble molecule that plays a crucial role as electron carrier in photosynthesis. It is synthesized exclusively by plants and certain bacteria. Humans require it as a dietary supply for blood coagulation and for calcium fixation in bones. Although the biosynthesis of phylloquinone has been tacitly assumed to have been defined for more than a decade, the comparative analysis of bacterial and plant genomes reveals that several enzymes involved in phylloquinone biosynthesis are missing. Moreover, plants have evolved an extraordinary metabolic architecture to synthesize this vitamin, including multiple events of gene fusion, highly diverged enzymes, and likely, a separated compartmentalization in chloroplasts and peroxisomes. Plant phylloquinone biosynthesis is also connected via shared intermediates to that of tocopherols (vitamin E), chlorophylls, and salicylate (a plant hormone). Combining comparative genomics, reverse genetics, metabolic profiling, metabolic engineering, and protein biochemistry, this project aims to characterize the missing key steps of phylloquinone biosynthesis, and to establish how plants regulate the flux splits between this pathway and other metabolic branches.Broader impacts: As plant-based foods represent the main source of dietary vitamin K for humans, this project will raise the awareness of phylloquinone and other plant micronutrient (vitamins, minerals, antioxidants) nutrition for children of the Nebraska 4-H program (Head, Hands, Heart, and Health). For that, the project will develop two presentations and a workshop during which children of middle-school age will learn to calculate how much of each vitamin they get per day during their meals at home and at school, and how these values compare to the recommended dietary intakes. This project will also contribute to the training of two undergraduate research assistants, two PhD students, and one postdoctoral associate in the laboratory of the PI.