MAPK phosphatases control plant immunity .

Kotryna Kvederaviciute, Institute of Biotechnology, Vilnius, Lithuania

Kotryna Kvederaviciute, Volodymyr Shubchynskyy, Michael Stumpe, Justinas Simulis, Felix Mauch, Alois Schweighofer and Irute Meskiene

Different defense responses, including activation of plant stress hormone production, are initiated by intracellular signaling pathways which are stimulated by pathogens. Pathogen-triggered immunity (PTI) includes phosphorylation-based activation of mitogen-activated protein kinases (MAPKs), which is counteracted by protein phosphatases. In Arabidopsis the pathogen-induced MAPKs MPK3, 4 and 6 play a role in the regulation of stress hormone production. In Arabidopsis MAPK phosphatases play an important role in the regulation of MAPK activities and can affect signaling responses. We have identified Arabidopsis PP2C-type protein phosphatases AP2Cs as MAPK phosphatases, which interact with and inactivate MPK3, 4, and 6. We found that these phosphatases dephosphorylate Arabidopsis MPK6 on phospho-T residue localized in the activation loop of the MAPK and inactivate its kinase activity. MAPK activation leads to reprogramming of plant cellular activities, including changes in plant stress hormone levels. Thus, we studied the role of AP2C PP2C-type MAPK phosphatases in regulation of kinase activities and salicylic acid and ethylene production during PTI. We correlated kinetic profiles of pathogen-induced kinase activities in phosphatase knock out and over expressing Arabidopsis plant lines with the production of stress hormones salicylic acid and ethylene. Our data show that over expression of the phosphatase leads to strong suppression of kinase activities, whereas in the absence of the phosphatase kinase activities are enhanced. We observed changes in ethylene amounts produced in these plants after pathogen-induced stress in comparison to wild type plants. Taken together, this work advances current understanding on regulation of MAPK signaling in plants and highlights the regulatory role ofPP2C type MAPK phosphatase in PTI.