Figure 2.

Pattern-recognition receptor (PRR)-mediated activation of mitogen-activated protein kinase (MAPK) cascades. In the chitin-triggered immune pathway, the chitin co-receptor CERK1 phosphorylates RLCK VII-4 members, which then phosphorylate the MAPK kinase kinases MAPKKK3/5 and MEKK1. This phosphorylation positively regulates the activation of two MAPKs, MPK3/6 and MPK4, respectively. The activated MPK3/6 and MPK4 further phosphorylate MAPKKK5 and MEKK1, respectively, further enhancing their activity. Other PRRs such as FLS2 and EFR activate MAPK cascade likely by employing other RLCKs, whose identity remains to be defined. SERKs, SOMATIC EMBRYOGENESIS RECEPTOR KINASES; p, phosphorylation.