MAPK3 and infection: Infection by pathogenic bacteria may also cause increased levels of H2O2 and NO, leading to higher endogenous melatonin level activation of the MAPK cascade via oxidative signal-inducible1/MAPKK kinases 3–MAPK kinases4/5/7/9-MAPK3/6 (OXI1/MAPKKK3-MAPKK4/5/7/9-MAPK3/6).