Ecological consequences of plant parasitism in Euphrasia

Parasitism is a ubiquitous phenomenon in the natural world, with dramatic evolutionary and ecological consequences for both the host and the parasite. There are over 3000 described parasitic plant species, including Rhinanthus, which maintains grassland ecosystems by stunting the growth of other herbaceous plants, and Striga, which decimates 12 billion dollars' worth of rice crops each year. While plant parasitism has a major effect on natural ecosystems, our understanding of the ecology of plant parasitism is surprisingly poor. In order to understand the origin and maintenance of plant parasitism, it is necessary to study the fitness benefit plant parasites receive from host attachment, and the genes associated with the parasitic plant syndrome.
This project investigates the ecological consequences of parasitism in Euphrasia, a group of generalist plant parasites which can grow independently, but grow more vigorously when attached to a suitable host plant. The genus includes c. 20 species in the UK, with each species showing notable habitat preferences (e.g. coastal, montane, meadow), and thus potentially different local host preferences, too. We have recently made seed collections from populations across the UK, as well as developed new genomic resources (whole draft-genome sequences), enabling us to investigate the ecological significance and genomic basis of parasitism and host preferences.
This project incorporates large-scale plant growth trials and cutting-edge gene expression data to address the following research questions:
1) Do Euphrasia species adapted to different habitats (montane vs coastal) have preferences for different host species?
2) What are the phenotypic and ecophysiological changes with alternative host attachment?
3) Are there major gene expression changes associated with attaching to different host plants?
In addition to answering these research questions, this project will also involve an industrial placement with CASE partner Scotia Seeds, the leading producer of wildflower seeds in Scotland. During a series of short placements throughout the PhD, the student will test germination protocols and procedures for growing Euphrasia as a commercial crop for wildflower seed mixes.
Overall, this project represents an exciting example of where the combination of growth trials and genomic tools may give insight into questions in evolutionary biology and food security challenges.
The core of this project relies on analysing fitness of plants grown with different hosts, in a large common garden experiment based at the Royal Botanic Garden Edinburgh (RBGE), and with additional trials at the Scotia Seed site. Seeds sourced from different habitats will be scored for vegetative vigour and seed set, to understand fitness when grown with a local vs. non-local host plant.
Other methods used in the project will be developed in line with the students' interests. Individuals with a strong interest in genomics will be able to use laser-dissection microscopy and tissue-specific RNA sequencing to study the gene expression changes at the host-parasite interface. This will reveal gene expression changes associated with host attachment. Alternatively, or in addition, students interested in ecology will use new tools to quantify ecophysiological changes associated with host attachment. Chlorophyll fluorescence is a powerful tool which could be used to investigate how parasitism could damage the photosynthetic apparatus of the host plant, and potentially enhance the photosynthetic capacity of the parasite. A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills. The student will be taught experimental design for common garden growth studies, how to produce next-generation sequencing data, a variety of genetic analyses (related to the analysis of gene expression data), and skills related to experiments in plant evolutionary biolo