Evolutionary consequences of facultative plant parasitism

寄生是自然界中的一种普遍现象，对寄主、寄生虫及其社区具有戏剧性的后果。已描述的寄生植物有3000多种，包括槲寄生、重要的草原植物犀牛和农业害虫Striga。一个特别有趣但研究很少的群体是兼性半寄生虫--它们可以独立于宿主生长和繁殖，但在宿主附着后生长得更旺盛。兼性半寄生代表了一种非常灵活的生长策略，在很大程度上被忽视了，而对专性寄生虫的研究--专性寄生虫是需要宿主完成其生命周期的有机体。本项目从进化遗传学的角度对兼性半寄生进行了个案研究。大戟属约有300种兼性半寄生，所有这些种都是兼性半寄生。这一建议将在两个方面向使用该属作为研究兼性半寄生的进化后果的研究系统方面取得进展。首先，它将提供资金来测试新兴的基因组方法，开发新的方案，并产生正在进行的研究所需的初步数据。这将包括测试一种新的叶绿体基因组浓缩方法，应用一种特定于组织的RNA测序方法，以及开发完整的基因组序列草案。这些资源将是未来确定兼性半寄生虫进化所涉及的基因座，以及测试植物寄生虫是否为适应性水平基因转移的载体所必需的。其次，这项提议将促进英国植物进化基因组学研究人员、世界植物寄生专家、植物基因组学领先者和幼发拉西亚生物学国际专家之间的国际合作。这种国际合作利用了美国寄生植物研究的悠久历史，以及以欧洲大陆为中心的幼发拉西亚生物学知识，以综合的方式解决关于半寄生的问题。加深对植物寄生的了解将极大地有益于许多研究领域，包括进化生物学、植物生物学、寄生虫学和基因组生物学。特别是，了解与寄生相关的基因组变化将为对主要生活史转变的遗传基础感兴趣的研究人员提供信息，而了解寄主附着过程中的转录变化将展示一个生物生命中基因表达变化的戏剧性例子。更广泛地说，确定不同植物寄生虫寄生生长的共同基因座，将有助于开发基因工具来对付作为农业害虫生长的寄生植物。

Parasitism is a widespread phenomenon in the natural world, with dramatic consequences for hosts, parasites, and their communities. There are over 3,000 described parasitic plant species, including mistletoes, the important grassland plant Rhinanthus, and the agricultural pest Striga. A particularly interesting, yet poorly studied group, are the facultative hemiparasites-which can grow and reproduce independent of a host, but grow more vigorously after host attachment. Facultative hemiparasitism represents a remarkably flexible growing strategy, which has largely been overlooked in preference of studies of obligate parasites-organisms which require a host to complete their lifecycle. This project investigates a case study of facultative hemiparasitism, from an evolutionary genetic perspective.The genus Euphrasia contains approximately 300 species, all of which are facultative hemiparasites. This proposal will make progress towards using this genus as a study system for investigating the evolutionary consequences of facultative hemiparasitism, on two fronts. Firstly, it will provide the funds to test emerging genomic approaches, develop new protocols, and produce preliminary data, required for ongoing research in Euphrasia. This will include testing a new chloroplast genome enrichment approach, applying a tissue-specific RNA sequencing method, and the development of a draft whole genome sequence. These resources will be essential for future work identifying loci involved in the evolution of facultative hemiparasites, and testing whether plant parasites are a vector for adaptive horizontal gene transfer. Secondly, this proposal will develop an international collaboration between a UK researcher in plant evolutionary genomics, the world expert in plant parasitism, a leader in plant genomics, and an international expert in the biology of Euphrasia. Such an international collaboration draws on the long history of research of parasitic plants in the USA, as well as the knowledge of Euphrasia biology centred in mainland Europe, to tackle questions about hemiparasitism in an integrated fashion.An increased understanding of plant parasitism will greatly benefit many areas of research, including evolutionary biology, plant biology, parasitology, and genome biology. In particular, understanding genomic changes associated with parasitism will be informative for researchers interested in the genetic basis of major life history transitions, while an understanding of transcriptional changes during host attachment will demonstrate a dramatic example of gene expression changes in the life of an organism. More generally, the identification of common loci underlying parasitic growth across diverse plant parasites, will facilitate the development of genetic tools to tackle parasitic plants that grow as agricultural pests.