Catalytic domain of the Serine/Threonine Kinases, Plant TEY Mitogen-Activated Protein Kinases
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Plant MAPKs are typed based on the conserved phosphorylation motif present in the activation loop, TEY and TDY. This subfamily represents the TEY subtype of plant MAPKs and is further subdivided into three groups (A, B, and C). Group A is represented by AtMPK3, AtMPK6, Nicotiana tabacum BTF4 (NtNTF4), among others. They are mostly involved in environmental and hormonal responses. AtMPK3 and AtMPK6 are also key regulators for stomatal development and patterning. Group B is represented by AtMPK4, AtMPK13, and NtNTF6, among others. They may be involved in both cell division and environmental stress response. AtMPK4 also participates in regulating innate immunity. Group C is represented by AtMPK1, AtMPK2, NtNTF3, Oryza sativa MAPK4 (OsMAPK4), among others. They may also be involved in stress responses. AtMPK1 and AtMPK2 are activated following mechanical injury and in the presence of stress chemicals such as jasmonic acid, hydrogen peroxide and abscisic acid. OsMAPK4 is also called OsMSRMK3 for Multiple Stress-Responsive MAPK3. In plants, MAPKs are associated with physiological, developmental, hormonal, and stress responses. Some plants show numerous gene duplications of MAPKs; Arabidopsis thaliana harbors at least 20 MAPKs, named AtMPK1-20. The TEY MAPK subfamily is part of a larger superfamily that includes the catalytic domains of other protein STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.