Coordination of Phytomelatonin and Salicylic Acid Signalling in Stomatal Closure.

Phytomelatonin (PMT) and salicylic acid (SA) play crucial roles in stomatal closure and immune regulation, yet their regulatory mechanisms are not fully understood. Here, we found that SA-induced stomatal closure and ROS production are dependent on the phytomelatonin receptor 1 (PMTR1) via regulating the expression of genes associated with cell wall peroxidases PRX33 and PRX34. Exogenous melatonin (exMT) induces the expression of genes related to SA biosynthesis (ICS1, PBS3), the receptor NPR1, as well as the effector transcription factors TGA1-3. Furthermore, exMT promotes the nuclear localisation of NPR1 through NO and GSH signalling in a PMTR1-dependent manner. Mutants of npr1, as well as tga1, tga2 and tga3, show partial sensitivity to PMTR1-mediated exMT signalling in stomatal closure. Either exMT or SA can significantly increase PMTR1 expression in Col-0, but not in npr1-1 and tga1 mutant plants. TGA1 can directly bind to the promoter elements of PMTR1 and activate its expression. Furthermore, the exMT- and SA-induced stomatal closure plays a vital role in preventing bacterial invasion in a PMTR1-dependent manner. Collectively, the results presented here demonstrate the coordination of PMTR1 and NPR1 in the regulation of PMT and SA signals in stomatal closure and immunity.