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

来自植物的特殊代谢物被人类使用了数千年，其中许多仍然是基本药物。然而，有时专门的代谢物是不受欢迎的，因为它们可能是苦的或有毒的。因此，操纵植物特有的新陈代谢是非常可取的，以产生更多的高价值化合物或减少某些植物部分中不需要的成分的水平。如今，这样的代谢工程在原则上是可能的。然而，更好地了解专业代谢物的生产和运输过程是有效工程的关键，而对于化学复杂的植物化合物来说，这一点往往是缺失的。该项目的目的是以柠檬苦素类化合物和类奎西诺类化合物为例获得此类知识。柠檬苦素类化合物和类奎西诺类化合物是非常有吸引力的工程目标。这些生物遗传相关的三萜类化合物主要存在于柑橘类植物(芸香科)和西马鲁巴科植物中。西马鲁巴科最著名的代表是世界各地的杂草臭椿，这是中国的天堂树。柠檬苦素类化合物是柑橘类水果苦味的罪魁祸首，而Quassinoid类化合物是中国天树为了消除竞争植物而分泌的，因为它们具有植物毒性。另一方面，柠檬苦素类化合物和类柠檬苦素类化合物都具有有益的性质：许多柠檬苦素类化合物是有效的杀虫剂或抗逆转录病毒药物；类柠檬苦素可以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类苦味素，为更好地利用有益的和避免消极的性质奠定基础。将采用三个子项目来实现这一目标：1)通过鉴定柑橘植物的生物合成基因来阐明柠檬苦素生产的生化基础。2)认识和开发柠檬苦素途径物流。转运蛋白将通过基因沉默来鉴定，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一步研究。3)中国天树的类天青素途径。将获得并分析来自不同组织的代谢组和转录组数据。这个项目将提供一个更好的理解柠檬苦素和类苦味素是如何在植物中产生和运输的，以及这种机制可能如何受到代谢工程的影响。此外，它将有助于扩大关于植物生物化学和植物专业代谢的一般知识。

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.