Investigating isoprenoid metabolism in the sunflower (Asteraceae) family

萜类化合物(或异戊二烯类化合物)是结构上最多样化的天然产物，有40,000多种已知化合物。萜烯合成酶和氧化酶[例如细胞色素P450单加氧酶(P450)]的协调生化反应催化从简单的前体分子异戊烯基二磷酸合成植物中独特的官能化(被氧化的)萜烯骨架。萜类化合物的巨大多样性是自然界中适应性酶进化的结果。为了解向日葵(菊科或菊科)植物适应性酶的进化、化学成分的多样性及其对植物生态适宜性的影响，我建议以向日葵(菊科或菊科)家族中的萜类代谢为模式系统进行研究。菊科植物最早出现在大约5000万年前的南美洲，随着菊科植物在不同环境中的大量物种形成，萜类化合物的一个特征亚类，称为倍半萜内酯，已经多样化。本研究的重点是从酶的进化和化学成分多样化的角度研究向日葵、生菜及相关菊科植物的倍半萜内酯代谢。这项提案将实现以下四个目标。将利用比较基因组学和代谢工程工具阐明向日葵和生菜中倍半萜内酯生物化学的细节；将研究不同细胞类型之间的代谢和/或蛋白质运输，以了解生菜中萜类代谢的细胞协调；受菊科植物中古老的P450酶的固有底物杂乱的启发，将尝试通过合理设计创造具有新催化功能的人工P450酶库；将通过分子方法评估倍半萜内酯立体化学变体对菊科植物抗虫害的影响。从这些综合方法中获得的数据将使我们能够增强我们对植物酶的进化和化学多样性的了解，并设计出改进的酶设计和植物防御的分子策略。

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.