Isoprenoid metabolism in compositae

类异戊二烯代谢提供了一种机制，将一种普遍存在的前体--焦磷酸异戊烯基酯引导到合成各种天然产物中。尽管所有生物都能产生异戊二烯类化合物作为其初级新陈代谢的一部分，但植物会合成第二层异戊二烯类化合物来增强它们的适应能力。目前已鉴定出50,000多种异戊二烯类化合物，并且有明确的证据表明，一些异戊二烯类化合物在植物生理、发育和与其他生物的相互作用中具有核心重要性。植物异戊二烯类化合物被人类用作药品、营养食品和工业产品，但由于其结构的复杂性，这些商品的化学合成往往是困难的。为了控制植物或其他异源系统中的类异戊二烯代谢，有必要提高类异戊二烯生物合成的基础知识。本文拟对菊科植物倍半萜内酯(SLS)的生化、转运和碳流进行研究，生菜、向日葵和药用植物青蒿属。将特别强调抗疟疾药物青蒿素(一种SL内过氧化衍生物)在黄花苜蓿中的生物合成。负责SL C11，13-双键还原和内酯环合成的基因将被鉴定和表征，倍半萜加氧酶中的结构-功能关系将使用嵌合细胞色素P450酶来分析。将在工程酵母系统和植物中对三磷酸腺苷结合盒转运体在倍半萜转运中的潜在参与进行严格的评估。我还将以向日葵毛状体为模型系统，研究SLS生物合成过程中的碳流。在毛状体中，将通过标记前体饲养试验、关键酶的原位免疫定位、原位RNA杂交和单细胞型基因组学来研究两种不同类型细胞(光合作用和非光合作用)的协调。所提出的多方面分析将阐明SLS是如何在菊科植物的毛状体中合成和运输的，并将为SL通量工程提供理论基础。

Isoprenoid metabolism provides mechanisms to channel a ubiquitous precursor, isopentenyl pyrophosphate, into the synthesis of a diverse array of natural products. Although all organisms can produce isoprenoids as part of their primary metabolism, plants synthesize a secondary layer of isoprenoids to augment their adaptation fitness. More than 50,000 isoprenoids have been identified, and clear evidence exists that some isoprenoids are of central importance in plant physiology, development, and interactions with other organisms. Plant isoprenoids have been used by humans as pharmaceuticals, nutraceuticals, and industrial products, but the chemical synthesis of these commodities is often difficult due to their structural complexities. To control the isoprenoid metabolism in plants or in other heterologous systems, it is necessary to advance the basic knowledge of isoprenoid biosynthesis. I propose here to study the biochemistry, transport, and carbon-flow of sesquiterpene lactones (SLs) in the plant family Compositae, to which lettuce, sunflower and medicinal plant sweet wormwood (Artemisia annua) belong. Specific emphasis will be given to the biosynthesis of the anti-malarial drug, artemisinin (an SL endoperoxide derivative), in A. annua. The genes responsible for the SL C11,13-double-bond reduction and lactone ring synthesis will be identified and characterized, and the structure-function relationship in the sesquiterpene oxygenase will be analyzed using chimeric cytochrome P450 enzymes. The potential involvement of ATP-Binding Cassette-transporters in sesquiterpenoid transport will be critically evaluated in an engineered yeast system and plants. I will also investigate carbon-flow in the biosynthesis of SLs using sunflower trichomes as a model system. In the trichomes, the coordination of two distinct cell types (photosynthetic and non-photosynthetic) will be studied by labeled precursor-feeding assays, in situ immunolocalization of key enzymes, in situ RNA hybridization, and single-cell-type genomics. The proposed multi-facet analysis will elucidate how the SLs are synthesized and transported in the trichomes of the Compositae and will provide a rationale for SL flux engineering.