Investigating isoprenoid metabolism in the sunflower (Asteraceae) family

萜类化合物（或类异戊二烯）是结构上最多样化的天然产物，已知化合物超过40,000种。萜烯合成酶和氧化酶[如细胞色素P450单加氧酶（P450）]的协同生化反应催化了从一个简单的前体分子二磷酸异戊烯基合成植物中独特功能化（氧化）的萜烯骨架。萜类化合物的巨大多样性是自然界适应性酶进化的结果。为了了解适应酶的进化、化学多样性及其对植物生态适应度的影响，我建议以向日葵（菊科）科)为模型系统研究萜类代谢。大约5000万年前，菊科植物首次出现在南美洲，萜类的一个特征亚类，称为倍半萜内酯，随着菊科植物在不同环境中的大规模物种形成而多样化。本课题重点从酶进化和化学多样化的角度研究向日葵、莴苣及相关菊科植物的倍半萜内酯代谢。这一建议将实现以下四个目标。比较基因组学和代谢工程工具将用于阐明向日葵和生菜中倍半萜内酯的生物化学细节；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；P450酶工程将以菊科植物P450酶固有的底物混杂性为灵感，通过合理的设计创造具有新型催化功能的人工P450酶池；倍半萜内酯的立体化学变异对菊科植物防御昆虫的影响将通过分子方法进行评估。从这些综合方法中获得的数据将使我们能够增强对植物酶进化和化学多样性的认识，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.