Genetic and phosphoproteomic basis of LysM-mediated immune signaling inMarchantia polymorphahighlights conserved elements and new aspect of pattern-triggered immunity in land plants

Abstract

AbstractPattern-recognition receptor (PRR)-triggered immunity (PTI) wards off a wide range of pathogenic microbes, playing a pivotal role in plant immunity. The model liverwortMarchantia polymorphais emerging as a popular model for investigating the evolution of plant-microbe interactions.M. polymorphatriggers defense-related gene expression upon sensing components of bacterial and fungal extracts, suggesting the existence of PTI in this plant model. However, the molecular components of the putative PTI inM. polymorphahave not yet been described. We show that, inM. polymorpha, which has four LysM receptor homologs, lysin motif (LysM) receptor-like kinase (LYK) MpLYK1 and LYK-related (LYR) MpLYR are required for sensing chitin and peptidoglycan fragments, triggering a series of characteristic immune responses. Comprehensive phosphoproteomic analysis ofM. polymorphain response to chitin treatment identified regulatory proteins that potentially shape LysM-mediated PTI. The identified proteins included homologs of well-described PTI components in angiosperms as well as proteins whose roles in PTI are not yet determined, including the blue-light receptor phototropin MpPHOT. We revealed that MpPHOT is required for a negative feedback of defense-related gene expression during PTI. Taken together, this study outlines the basic framework of LysM-mediated PTI inM. polymorphaand demonstrates the utility ofM. polymorphaas a plant model for discovering novel or fundamental molecular mechanisms underlying PRR-triggered immune signaling in plants.