Interaction between Marchantia polymorpha and Phytophthora palmivora

Associations with symbiotic microbes and successful defences against pathogens contributed to the expansion of plants on land. Symbiotic interactions are well described in extant early land plants such as liverworts and hornworts, yet interactions with biotrophic pathogens remain unexplored. Here, we assessed several liverwort species for susceptibility to the oomycete pathogen Phytophthora palmivora. We demonstrate that P. palmivora establishes a biotrophic interaction with Marchantia polymorpha that is restricted to photosynthetic air chambers. Pathogen growth was attenuated in air-chamber less nop1 mutants, revealing an architectural requirement for colonization. In response to infection, M. polymorpha activates conserved basal defences and envelopes uncharacteristic intracellular hyphal structures with host-derived membranes. Strikingly, we observed the colonization-induced expression and interface-localization of MpSYP13B, extending the importance of symbiosis-associated syntaxins to pathogen interfaces. These data demonstrate the accessibility of liverworts for manipulation by pathogens and suggest commonalities between defense and symbiosis in early land plants.