Extracellular diadenosine tetraphosphate (Ap4A) is recognized by the plasma membrane purinoreceptor P2K1/DORN1 and closes stomata in Arabidopsis thaliana

O_LIDinucleoside polyphosphates (NpnNs) are considered novel signalling molecules involved in the induction of plant defence mechanisms. However, the NpnNs signal recognition and transduction are still enigmatic. Here we report, for the first time, that diadenosine tetraphosphate (Ap4A) is recognized by the Arabidopsis thaliana purinoreceptor P2K1/DORN1 (Does Not Respond to Nucleotides 1) and causes stomatal closure. C_LIO_LIExtracellular Ap4A- and dicytidine tetraphosphate (Cp4C)-induced stomatal closure was observed using a microscope. Reactive oxygen species (ROS) accumulation was determined by staining with nitroblue tetrazolium (NBT) and 3,3'-diaminobenzidine tetrahydrochloride (DAB). Transcriptional changes were determined by quantitative real-time PCR. Wild-type Col-0 and the dorn1-3 A. thaliana knockout mutant were used. C_LIO_LIExamination of the leaf epidermis dorn1-3 mutant provided evidence that P2K1/DORN1 recognizes extracellular Ap4A but not Cp4C. ROS are involved in signal transduction caused by Ap4A and Cp4C, leading to stomatal closure. Ap4A induced and Cp4C suppressed the transcriptional response in wild-type plants. Moreover, in dorn1-3 leaves, the effect of Ap4A on gene expression was impaired. C_LIO_LIOur research demonstrated, for the first time, that P2K1/DORN1 is a plant purinoreceptor for Ap4A. This interaction leads to changes in the transcription of signalling hubs in signal transduction pathways. C_LI