Limonoids and Quassinoids – Understanding and Harnessing Complex Triterpene Production and Transport in Plants

植物中的特殊代谢物已被人类使用了数千年，其中许多仍然是必需的药物。然而，有时候，专门的代谢物是不需要的，因为它们可能是苦的或有毒的。因此，非常需要操纵植物专门的代谢以产生增加量的高价值化合物或降低某些植物部分中不需要的组分的水平。这种代谢工程在今天原则上是可能的。然而，更好地了解特定代谢物的生产和运输过程是高效工程的关键，而这对于化学复杂的植物化合物来说往往是缺失的。该项目的目的是以柠檬苦素和苦木素为例，获得此类知识。鲎和苦木类是非常有吸引力的工程目标。这些生物学上相关的三萜主要分别在柑橘类植物（芸香科）和苦木科中产生。苦木科最著名的代表是世界性的杂草臭椿，中国的天堂树。柑橘类水果的苦味是由柠檬酸造成的，而苦木素是由中国天堂树分泌出来的，由于它们的植物毒性，它们可以消除竞争植物。另一方面，柠檬苦素和苦木素都具有有益的特性：许多柠檬苦素是有效的杀虫剂或抗逆转录病毒剂;苦木素可用作除草剂或抗癌药物。该项目的目的是分析植物如何产生和运输柠檬苦素和苦木素，为更好地利用有益特性和避免负面特性奠定基础。本研究拟通过以下三个子项目来实现这一目标：1）通过鉴定柑橘类植物的生物合成基因来阐明柠檬苦素类化合物产生的生化基础。2)理解和利用柠檬苦素途径物流。转运蛋白将通过基因沉默进行鉴定，使用卵母细胞表达系统进行生化测试，并使用荧光底物类似物进行进一步研究。3)中国天堂树中类苦木素途径的剖析。将获得并分析不同组织的代谢组和转录组数据。该项目将更好地了解柠檬苦素和苦木素是如何在植物中产生和运输的，以及这种机制如何受到代谢工程的影响。此外，它将有助于扩大有关植物生物化学和植物专门代谢的一般知识。

Specialised metabolites from plants have been used by mankind for thousands of years, many of which are still essential medicines. Sometimes, though, specialised metabolites are unwanted, as they can be bitter or poisonous. Manipulating plant specialised metabolism is therefore highly desirable to produce increased quantities of high-value compounds or to reduce levels of unwanted components in certain plant parts. Such metabolic engineering is nowadays possible in principle. However, a better understanding of the processes underlying the production and the transport of specialised metabolites is key for efficient engineering, which is often missing for chemically complex plant compounds. The aim of this project is to obtain such knowledge using limonoids and quassinoids as an example. Limonoids and quassinoids are highly attractive targets for engineering. These biogenetically related triterpenes are mainly produced in citrus plants (Rutaceae) and in Simaroubaceae, respectively. The most well-known representative of the Simaroubaceae is the cosmopolitan weed Ailanthus altissima, the Chinese tree of heaven. Limonoids are responsible for the bitter taste of citrus fruits, whereas quassinoids are excreted by the Chinese tree of heaven to eliminate competing plants due to their phytotoxic properties. On the other hand, both limonoids and quassinoids possess beneficial properties: Many limonoids are potent insecticides or antiretroviral agents; quassinoids could be used as herbicides or as anti-cancer drugs. The aim of this project is to analyse how plants produce and transport limonoids and quassinoids, to establish a basis for better use of beneficial as well as avoidance of negative properties. Three subprojects will be employed to fulfil this aim: 1) Elucidating the biochemical basis of limonoid production by identifying biosynthesis genes from citrus plants. 2) Understanding and exploiting limonoid pathway logistics. Transporters will be identified by gene silencing, tested biochemically using an oocyte expression system and studied further using fluorescent substrate analogues. 3) Profiling quassinoid pathway in Chinese tree of heaven. Metabolome and transcriptome data from different tissues will be obtained and analysed. This project will provide a better understanding how limonoids and quassinoids are produced and transported in plants, and how this machinery can potentially be affected by metabolic engineering. Additionally, it will help to expand the knowledge about plant biochemistry and plant specialised metabolism in general.