A receptor-like kinase pair integrates extracellular ATP and salicylic acid signaling to activate plant immunity.

Extracellular Adenosine 5'-triphosphate (eATP) is a damage-associated molecular pattern in both plants and animals, playing an important role as a danger signal in response to various environmental stresses. eATP works both independently and in coordination with other signaling pathways. Here, we identify a previously uncharacterized proline-rich extensin-like receptor kinase 15 (PERK15), which interacts with the plant eATP receptor P2K1 and integrates eATP and salicylic acid (SA)-mediated pathogen defense responses. perk15 mutant plants display reduced eATP responses and compromised pathogen resistance, whereas ectopic overexpression of PERK15 triggers autoimmunity. eATP treatment enhances PERK15-P2K1 interaction. P2K1-mediated phosphorylation of a Ser/Thr cluster in the PERK15 kinase domain is essential for its activation. PERK15 transcript levels are upregulated by SA, and PERK15 overexpression promotes the protein accumulation of the SA receptor NPR1. Data show that eATP and SA act synergistically to regulate plant defense responses in a PERK15-dependent manner. Together, the findings identify PERK15 as a key node linking eATP and SA signaling, providing insights into how plants integrate extracellular danger signals and defense hormone signals to mount effective immune responses.