The Arabidopsis Mitogen-Activated Protein Kinase Kinase Kinase 20 (MKKK20) C-terminal domain interacts with MKK3 and harbors a typical DEF mammalian MAP kinase docking site.

Mitogen-activated protein kinase (MAPKs) constitute a major component in plant cellular signaling considering the sheer number of MAPKKKKs, MAPKKKs, MAPKKs and MAPKs when compared to yeast and animal systems. Nevertheless, only few complete MAPK cascades have been deciphered and the same hold true for their substrates. Furthermore, cascades often share kinase components, but little is known about their specific interactions and domains. The Arabidopsis thaliana MAP kinase kinase kinase 20 (MKKK20) was recently showed to interact with MKK3 and MPK18 in two non-complementary signaling cascades involved in root cortical microtubule functions. Here, MKKK20 and MKK3 proteins where dissected and tested in yeast two-hybrid assays followed by an in planta validation through bimolecular fluorescence complementation (BiFC) assays and showed that the MKKK20 C-terminal region interacted with MKK3 that comprised a typical DEF domain akin to MAPKs docking domains.