Serine/threonine kinase which acts as an essential component of the MAP kinase signal transduction pathway to regulate proliferation, differentiation and effect cell fate decisions in various tissues (PubMed:8157002, PubMed:19965758, PubMed:22140578, PubMed:27552662). Required downstream of phl/Raf in the sev/sevenless, tor/torso, and EGF receptor homolog Egfr signal transduction pathways (PubMed:8157002). Required for embryonic epithelial tissue repair (PubMed:22140578). During larval development, mediates Ptth/tor signaling leading to the production of ecdysone, a hormone required for the initiation of metamorphosis (PubMed:19965758). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Activated by tyrosine and threonine phosphorylation. In third instar larvae, expressed in eye imaginal disks. In adults, expressed in head and body. Embryos, larvae and adults. The TXY motif contains the threonine and tyrosine residues whose phosphorylation activates the MAP kinases. Dually phosphorylated on Thr-198 and Tyr-200, which activates the enzyme (By similarity). Phosphorylated on tyrosine residue(s) in response to insulin. Embryonic wound healing defects (PubMed:22140578). RNAi-mediated knockdown in the prothoracic gland (PG) delays the onset of pupariation by prolonging the L3 larval stage and increases adult weight (PubMed:19965758). Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. MAP kinase subfamily.