Enzyme structure, function, and evolution in flavonoid biosynthesis

Abstract

Plant specialized metabolism is a key evolutionary adaptation that has enabled plants to migrate from water onto land and subsequently spread throughout terrestrial environments. Flavonoids are one particularly important class of plant specialized metabolites, playing a wide variety of roles in plant physiology including UV protection, pigmentation, and defense against herbivores and pathogens. Flavonoid diversity has increased in conjunction with land plant evolution over the past 470 million years. This dissertation examines the structure, function, and evolution of enzymes in the flavonoid biosynthetic pathway. First, we structurally and biochemically characterized orthologs of chalcone synthase (CHS), the enzyme that catalyzes the first step of flavonoid biosynthesis, from diverse plant lineages. By doing so, we gained insight into the sequence changes that gave rise to increased reactivity of the catalytic cysteine residue in CHS orthologs in euphyllophytes compared to basal land plants. We then developed methods and transgenic plant lines to study the in vivo function of these CHS orthologs, as well as whether their functional differences play a role in redox-based regulation of flavonoid biosynthesis. Finally, we examined enzymes involved in the biosynthesis of galloylated catechins, a highly enriched class of flavonoids in tea that are thought to have health benefits in humans. These findings contribute to an understanding of the evolution of enzyme structure and function in flavonoid biosynthesis, and how it has facilitated the adaptation of plants to a wide variety of terrestrial habitats.