A bacterial lipid triggers membrane mechanosensing immunity in Arabidopsis

The plant immune system engages cell-surface receptors that detect microbe-associated molecular patterns to initiate pattern-triggered immunity (PTI), and intracellular receptors that sense microbe-secreted effectors to activate effector-triggered immunity (ETI). Whether additional modes of microbial detection exist remains unclear. Here, we define membrane mechanosensing immunity (MSI), a third layer of immune signaling. A bacterial lipid, the main diffusible signal factor (DSF) from Xanthomonas campestris pv. campestris, acts as a membrane-active molecule that alters plasma membrane biophysical properties, activates Mechanosensitive Channel of Small Conductance (MscS)-like (MSL)-dependent immune signaling, and triggers a broad transcriptional reprogramming that overlaps with PTI and ETI. MSI modulates PTI signaling and requires both PTI and ETI components for effective disease resistance. These findings establish the sensing of metabolite-induced membrane perturbations as a mechanism of microbial detection.