Ergosterol‐induced immune response in barley involves phosphorylation of phosphatidylinositol phosphate metabolic enzymes and activation of diterpene biosynthesis

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 in plants remain largely unknown. Here, we investigate the immune responses activated in barley (Hordeum vulgare) by lipid extracts from the beneficial root endophytic fungus Serendipita indica and compare them to responses elicited by chitohexaose and the fungal sterol ergosterol. We demonstrate that S. indica lipid extract induces hallmarks of pattern‐triggered immunity (PTI) in barley. Ergosterol emerged as the primary immunogenic component and was detected in the apoplastic fluid of S. indica‐colonized barley roots. Notably, S. indica colonization suppresses the ergosterol‐induced burst of reactive oxygen species (ROS) in barley. By employing a multi‐omics approach, which integrates transcriptomics, phosphoproteomics, and metabolomics, we provide evidence for the phosphorylation of phosphatidylinositol phosphate (PIP) metabolic enzymes and activation of diterpene biosynthesis upon exposure to fungal lipids. Furthermore, we show that phosphatidic acid (PA) enhances lipid‐mediated apoplastic ROS production in barley. These findings indicate that plant lipids facilitate immune responses to fungal lipids in barley, providing new insights into lipid‐based signaling mechanisms in plant–microbe interactions.