Plant Lipids Mediate Immune Responses to Fungal Lipids in Barley

Lipids play crucial roles in plant-microbe interactions, functioning as structural components, signaling molecules, and microbe-associated molecular patterns (MAMPs); however, the mechanisms underlying lipid perception and signaling pathways in plants remain largely unknown. This study investigates the immune responses triggered in Hordeum vulgare (barley) by lipid extracts from the root endophytic fungus Serendipita indica. We compare these responses to those elicited by the carbohydrate MAMP chitohexaose and the fungal sterol lipid ergosterol, a 5,7-diene oxysterol recognized as a MAMP in plants. Our results demonstrate that S. indica lipid extract induces hallmarks of pattern-triggered immunity (PTI) in barley. Ergosterol was identified as the main immunogenic component and was detected in the apoplastic fluid of S. indica-colonized barley roots. Using a multi-omics approach combining transcriptomics, phosphoproteomics, and metabolomics, our data provide evidence for the activation of phosphatidylinositol phosphate (PIP) signaling and diterpene biosynthesis upon exposure to fungal lipids. Furthermore, we show that phosphatidic acid (PA) enhances lipid-mediated apoplastic reactive oxygen species (ROS) production in barley. These findings indicate that plant lipids mediate immune responses to fungal lipids in barley, advancing our understanding of lipid perception and signaling in plant-microbe interactions.