Investigating isoprenoid metabolism in the sunflower (Asteraceae) family

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Terpenoids (or isoprenoids) are structurally the most diverse natural products with more than 40,000 known compounds. Coordinated biochemical reactions of terpene synthase and oxidase enzymes [e.g., cytochrome P450 monooxygenase (P450)] catalyze the synthesis of uniquely functionalized (oxidized) terpene backbones in plants from a simple precursor molecule, isopentenyl diphosphate. The enormous diversity of terpenoids is the outcomes of adaptive enzyme evolutions in nature. In order to understand the adaptive enzyme evolution, chemical diversification, and its influence on the plant eco-fitness, I propose to investigate the terpenoid metabolism in the sunflower (Asteraceae or Compositae) family as a model system. Plants in the Asteraceae family first emerged in the South America about 50 million years ago, and a characteristic sub-class of terpenoid, called sesquiterpene lactone, has diversified alongside the massive speciation of the Asteraceae plants in distinct environments. A specific focus in this proposal is to study sesquiterpene lactone metabolism in sunflower, lettuce and related Asteraceae plant species from the perspectives of enzyme evolution and chemical diversification. Four objectives listed below will be achieved from this proposal. Comparative genomics and metabolic engineering tools will be used to elucidate the details of the sesquiterpene lactone biochemistry in sunflower and lettuce; Metabolic and/or protein trafficking among different cell types will be investigated to understand the cellular coordination of terpenoid metabolisms in lettuce; Inspired by the innate substrate promiscuity of ancient P450s identified in Asteraceae family, P450 enzyme engineering will be attempted to create a pool of artificial P450 enzymes with novel catalytic functions by rational design; The impact of stereo-chemical variants of sesquiterpene lactone on the defense of the Asteraceae plant against insects will be assessed by molecular methods. The data obtained from these integrative approaches will enable us to enhance our knowledge of the plant enzyme evolution and chemical diversification and to devise the improved molecular strategies for enzyme design and plant defense.