NIK kinases link phytocytokine perception to early plant immune phosphorylation

Plant danger signals known as phytocytokines can activate immune responses, but the molecular events that propagate these signals through cell-surface receptor complexes have remained incompletely understood. A study in Arabidopsis identifies all six members of the nuclear-shuttle-protein-interacting kinase (NIK) family as non-canonical, signal-propagating components of phytocytokine receptor complexes. Reported in Nature Plants , the research shows that NIK kinases contribute redundantly but distinctively to immune responses triggered by Pep and SCOOP12, with their activity linked to early phosphorylation events and downstream signalling proteins.

The investigators examined how NIK proteins relate to the phytocytokine receptors PEPR1 and MIK2 and the co-receptor BAK1. NIKs associated with these proteins, and ligand perception transiently enhanced the interactions. These results place the kinases within multiple phytocytokine receptor complexes in which they appear to relay signals rather than act simply as structural components.

The experimental system was the model plant Arabidopsis , and the findings concern plant immune signalling at the molecular level rather than effects in crops, animals or human disease. Phosphorylation experiments provided further evidence that NIKs operate in the pathway downstream of receptor perception. NIK1, NIK3 and NIK6 underwent robust, ligand-dependent phosphorylation that required PEPR signalling.

Both PEPR1 and BAK1 could phosphorylate NIK proteins, indicating that the kinases receive phosphorylation inputs from two components of the receptor system. NIKs were dispensable for the Pep2-induced association between PEPR1 and SERK, showing that they are not required for that initial receptor pairing. They were, however, required for the receptor complex to produce its full phosphorylation output, for efficient recruitment of BIK1 and PBL1, and for activation of BIK1.

The results therefore distinguish two stages of signalling: NIKs were unnecessary for the measured PEPR–SERK association but important for the phosphorylation capacity and downstream protein activation that followed. Genetic complementation refined the mechanism by identifying two phosphorylation sites in NIK1, Ser615 and Tyr618, as essential for NIK1-mediated immune signalling. Restoring function at the relevant sites demonstrated that both residues are required, while Tyr618 preferentially controlled the recruitment and phosphorylation of BIK1.

Taken together, the experiments support a model in which phytocytokine perception is propagated through NIK-associated phosphorylation events, extending immune signalling beyond the initial PEPR1–BAK1 and PEPR1–SERK receptor interactions. The work identifies NIKs as contributors to full phosphorylation output and efficient downstream activation in the tested Arabidopsis pathways, rather than demonstrating that they are required for every aspect of the plant immune response.

Subject of Research: Molecular regulation of phytocytokine-triggered plant immunity in Arabidopsis

Article Title: NIK receptor kinases propagate phytocytokine-triggered immunity by driving early phosphorylation events

Article References: Zhu, W., Huang, M., Li, X., Lin, Y., Xie, J., Cheng, J., Fu, Y., Jiang, D., Tsuda, K., Yu, X., & Li, B. (2026). NIK receptor kinases propagate phytocytokine-triggered immunity by driving early phosphorylation events. Nature Plants. https://doi.org/10.1038/s41477-026-02439-w

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02439-w

Keywords: Arabidopsis, plant immunity, NIK kinases, phytocytokines, PEPR1, BAK1, protein phosphorylation, receptor complexes, danger signals, SCOOP12, receptor, kinases