A disulfide bond sculpts the CTNIP4 phytocytokine fold for recognition by the receptor kinase HSL3

Abstract

Abstract Precise ligand recognition by closely related leucine-rich repeat receptor kinases (LRR-RKs) is essential for plants to coordinate immunity, development and environmental adaptation. Here we show how the LRR-RK HSL3/NUT specifically recognizes the folded, disulfide-stabilized CTNIP4/SCREW2 phytocytokine in Arabidopsis . Quantitative binding assays define a minimal CTNIP4 region required for high-affinity HSL3 interaction and signalling activation. A 2.12-Å crystal structure of the HSL3–CTNIP4 complex reveals a unique C-terminal receptor pocket that accommodates the peptide’s cyclic architecture through a combination of hydrophobic and polar contacts, a feature absent in the closely related HAE/HSL LRR-RKs. The cyclic CTNIP4 fold further establishes a largely hydrophobic interface that bridges HSL3 to the SERK co-receptor, forming a distinct activation surface. Together, these structural, biochemical and physiological insights uncover a previously unrecognized mechanism of CTNIP4 peptide perception and HSL3 receptor activation, highlighting how subtle architectural variations enable precise ligand selectivity among highly conserved plant receptor kinases.

The authors' abstract, as published at the source. Nature Plants, 2026 · DOI ↗