MKK9-MPK3/MPK6 module phosphorylates and activates EIN3, leading to the promotion of EIN3-mediated transcription in ethylene signaling. Autophosphorylates and also phosphorylates MPK3 and MPK6. Plays an important role in ethylene and camalexin biosynthesis and in salt stress response. MKK9-MPK6 module positively regulates leaf senescence. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Translocated into the nucleus by ACC treatment. Up-regulated during leaf senescence. By Alternaria brassicae pathogen infection. Phosphorylation at Ser-195 and Ser-201 by MAP kinase kinase kinases positively regulates kinase activity. Autophosphorylated (Probable). Broad spectrum of moderate ethylene-insensitive phenotypes. Reduced salt sensitivity. Delayed senescence phenotype. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.