Cross-ribbon conformation defines peptide recognition in SCREW/CTNIP-NUT/HSL3 signalling.

Plants balance gas exchange with pathogen defense through dynamic stomatal regulation. Stomata close temporarily during pathogen attack to limit invasion, then reopen to restore photosynthesis and transpiration while lowering apoplast water saturation to inhibit pathogen proliferation. The secreted peptides, SCREW/CTNIP promote stomatal reopening through the receptor NUT/HSL3 and co-receptor BAK1/SERK3, thereby counteracting ABA and MAMP-triggered stomatal closure. Here we present the cryo-EM structures of AtNUTECD and the AtNUTECD-SCREW2/CTNIP4-AtBAK1ECD complex, uncovering a distinctive peptide-receptor interaction mechanism. SCREW2 adopts a unique cross-ribbon conformation that distinguishes it from other known conformations of LRR-RK-binding peptides, enabling its specific recognition by AtNUT and subsequent recruitment of AtBAK1. An N-linked glycan at N449 within the SCREW2-AtNUT binding interface is required for efficient SCREW2 recognition. Mutations in SCREW2 recognition sites significantly attenuated downstream MAPK activation and PTI marker gene expression.