Modulation of lineage-specific oil body development and defense against gastropod herbivory in Marchantia polymorpha...

The transition to land exposed early plants to new biotic pressures, driving the evolution of the plant immune system. Extant land plants comprise two major groups, tracheophytes and bryophytes, which include liverworts, hornworts, and mosses. These two groups diverged early after land colonization, and thus, immune mechanisms have also been subjected to independent evolution. In tracheophytes, the NONEXPRESSOR OF PATHOGENESIS-RELATED GENES (NPR) family of proteins serve as salicylic acid sensors regulating responses against (hemi)biotrophic pathogens. Here, we investigated the function of the unique NPR in the liverwort Marchantia polymorpha and found that it exhibits a specialized immune function relative to its orthologs in tracheophytes. We show that in response to environmental cues, MpNPR acts as a positive modulator of the content of oil bodies, a synapomorphy of liverworts, which function as storage organelles for secondary metabolites and defense against arthropods. We found that MpNPR interacts with MpERF13, a master transcription factor controlling oil body differentiation, and that plants with altered levels of MpNPR are misregulated in MpERF13-dependent gene expression. Furthermore, we uncover that MpNPR and MpERF13 are required for defense against snail herbivory. Finally, we found that the ability of MpNPR to induce oil body formation and resistance to gastropods is dependent on MpERF13. Altogether, our results show that MpNPR acts as a positive regulator of the oil body content by activating MpERF13 in response to environmental cues. Moreover, we uncover that MpNPR, MpERF13, and oil bodies are required for immunity against gastropod herbivory in Marchantia. Our results pinpoint a novel specialized evolutionary trajectory of NPR in liverworts.