This summer I was very fortunate to join Dr Phil Carella’s lab at the John Innes Centre in Norwich to investigate natural variation of plant immunity. I joined an enthusiastic team who are interested in understanding how plant immunity evolved and exploring the diversity of defences across distantly related plants. To tackle these questions, the lab uses macroevolutionary analyses and molecular genetic tools working with different evolutionarily insightful models. During my placement I was mainly involved in working with two model organisms that diverged more than 400 million years ago: Marchantia polymorpha (model liverwort) and Arabidopsis thaliana (model angiosperm). The overall goal of my work was to challenge those species with different broad-host range pathogens to eventually understand the molecular basis of the newly described plant-microbe interactions. This knowledge can be effectively applied in any plant protection endeavours be it agronomically-important crops or ornamental plants. During my summer project I was mainly interested in natural variation within plant species to investigate how a small heterogeneity between ecotypes could shine a spotlight onto the genes crucial for plant immunity.
The first pathosystem I worked with was Arabidopsis thaliana and Phytophthora palmivora. Arabidopsis is a representative of flowering plants that are well described and widely used in plant genetic research. Phytophthora species are oomycete (fungus-like) microorganisms that cause root rot, seed rot and damping-off of seedlings in the wide range of economically important crops. Here, I worked with P. palmivora that infects many tropical plants including cacao trees, citrus, durian and mango. Previously my lab identified that a commonly used A. thaliana ecotype, Col-0, was completely resistant to P. palmivora infection. It was unknown if this resistance was specific to the Col-0 ecotype or was conserved throughout the species. To answer this question, I attempted to screen 96 different A. thaliana ecotypes found across the world to explore the heterogeneity in their immune response. I first grew the plants for 3-4 weeks and then infected them with a standardised amount of P. palmivora spores. It was crucial to carefully plan and conduct my experiments in parallel to ensure I was using the time efficiently. I then compared the phenotypes 5 days post infection using my own symptom scale. A wide heterogeneity of responses was found where Ler-0 and Gly-0 ecotypes were most susceptible to the infection, Cvi-0 and Ei-2 were least susceptible and multiple ecotypes had a mixed response. Now the lab is motivated to explore the molecular basis behind such variation using transcriptomics and genome comparison studies.
I then looked at a different pathosystem involving M. polymorpha and P. palmivora. Marchantia is a representative of liverworts that are the earliest divergent land plant lineage and can be used for macroevolutionary comparisons. In contrast to Arabidopsis, Marchantia was susceptible to all known P. palmivora strains. Here, the endeavour was split where some group members decided to run comparisons and investigate the variation within Marchantia species. In addition, I decided to explore plant-microbe interactions from a different perspective and consider variation in the Phytophthora virulence. The goal was to screen Marchantia (TAK1 – model ecotype used) against different Phytophthora species and compare their virulence profiles. I first propagated 15 different Phytophthora strains and then used them for infection of 3-weeks old Marchantia. A qualitative scoring system was used to rank the plant symptoms 3, 5 and 7 days post infection. It was found that P. cambivora and P. cryptogea were almost non-virulent towards Marchantia, in contrast to multiple P. parasitica strains that showed an extremely virulent profile. Now the lab is motivated to dissect the molecular basis behind the varied virulence to understand the molecular mechanisms that make some strains more virulent towards Marchantia than others.
During my internship I have thoroughly enhanced my general research skills such as experimental design and troubleshooting as well as field-specific skills in plant tissue culture, infections and microbiology. I am very thankful to the BSPP for providing me with an opportunity to grow as a scientist and gain valuable research experience. I would also like to express my heartfelt gratitude to Dr Phil Carella, Dr Kristina Grenz and Dr Khong-Sam Chia for their strong support and encouragement.
University of Bristol