2. Collecting wild-type accessions of Marchantia (and Lunularia). David J. Hoey1,2., George Greiff1., Ed Harris1,2., Karima El Mahboubi3., Santiago Farias1., Philip Carella1,4., SLCU Outreach Consortium1., Pierre-Marc Delaux3., Sebastian Schornack1,2. 1.Sainsbury Laboratory, University of Cambridge, United Kingdom; 2.Department of Plant Sciences, University of Cambridge, United Kingdom; 3.Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, Centre National de la Recherche Scientifique, Université Paul Sabatier, INP Toulouse, France; 4.John Innes Centre, Norwich, United Kingdom. Natural variation in oomycete infection of Marchantia polymorpha 6. qPCR quantification of Phytophthora infection across accessions is in progress, with a goal of a linear assembly of this trait. 7. Future steps: genome wide association studies will reveal novel factors of resistance/susceptibility in this model pathosystem. 1. Introduction • Liverwort and angiosperm lineages diverged around 450 million years ago. • Infection of Marchantia polymorpha has been established as a model pathosystem for macroevolutionary studies in oomycetes, fungus, and bacteria. • Phytophthora palmivora is a hemi-biotrophic broad-host, and infects through air chambers and colonises the upper photosynthetic layer. • Most studies of Marchantia are on a small number of accessions, and the genomic resources which are available for other more established model organisms are not currently available. • Our aim is to establish these genetic resources, and our working hypothesis is that variation in the infection of natural accessions of Marchantia is caused by variable genetic elements. We have so far collected 92 accessions of Marchantia polymorpha: some through our citizen science project, and some by us and collaborators on field trips or holidays! Male and female accessions were determined by amplification of PCR markers. Summary & Conclusions: • Marchantia polymorpha and Phytophthora palmivora are a model pathosystem for macroevolutionary studies. • However, as a relatively new model system the genetic resources which are available for other systems are not yet established. • We are working to establish these resources for the community by collecting and sequencing accessions. • Most accessions display intermediate symptoms, though some are very resistant and some are very susceptible. • None of the accessions tested so far are completely resistant to the pathogen. • We plan to use the Marchantia-Phytophthora pathosystem as a quantitative trait for future genome-wide association studies. Initial proof-of-concept experiment. qPCR data showing 2 susceptible, 2 intermediate, and 2 resistant accessions collected at a single time point. N=4, each data point performed in triplicate. Each sample contains 3 individual plants. Statistical groupings from Tukey's HSD post-hoc analysis. In meta-analysis of separate infection experiments, we will use TAK1 (susceptible) and TAK2 (resistant) as baselines for pathogen biomass. Acknowledgements: Thanks to all of the Schornack group for useful discussions and contributions. Thank you to Elisa Mogollon-Perez for regular maintenance of these lines. Thank you to the SLCU Events team for their coordination of the outreach events. This project was funded by the Gatsby Foundation. The members of the SLCU Outreach Consortium who contributed to the Great British Liverwort Hunt project are as follows: David Hoey, Sebastian Schornack, Edwige Moyroud, Alan Wanke, Alessandra Bonfanti, Stefano Gatti, Lauren Gardiner, Martin Balcerowicz, Alexander Summers, Elisabeth Burmeister, Kathy Grube, Andreea Alexa, Nataliia Kuksa, Jemma Salmon, Bryony Yates, Lucie Riglet, Elena Salvi, Ian Burrow, David G. Hill, The Roberts Family, Peter & Theresa Rooney, Jennie Showers, Anthea Wilson, and 59 anonymous contributors from the British public. Email/crsID: djh248@cam.ac.uk Twitter: @DavidJHoey Infected Marchantia polymorpha (5dpi) 3. WT accessions of Mar