MAPK phosphatases control plant immunity.

Alois Schweighofer,Institute of Biotechnology, Vilnius, Lithuania

Volodymyr Shubchynskyy, Kotryna Kvederaviciute, Irute Meskiene, Alois Schweighofer

All cells perceive signals from the environment and transmit this information inside to induce corresponding responses, where mitogen-activated protein kinases (MAPKs) are the central players in cell signaling. Bacterial pathogens activate Arabidopsis thaliana MAPKs MPK3, MPK4 and MPK6. The activity of MAPKs is controlled by protein phosphatases. The aim of our study is to determine the roles of Arabidopsis MAPK phosphatases, their intracellular co-localisation/interaction with the substrate MAPKs and to unfold their contribution to plant pathogen responses. We identified Arabidopsis MAPK phosphatases of PP2C-type (belonging to the family of Ser/Thr protein phosphatases) AP2Cs, to control MAPK activities and thus affect cell signaling responses during plant attack by pathogens. These phosphatases interact with and inactivate MPK3, MPK4 and MPK6. Visualization of the protein-protein interactions between AP2Cs and MAPKs in vivo using bimolecular fluorescent complemenation (BiFC) in isolated plant cells reveals fluorescence in the cytoplasm and nucleus. We show that AP2C dephosphorylates Arabidopsis MPK6 on phospho-Thr in the activation loop of the MAPK and thereby inactivates its kinase activity in plants. MAPK activation in plants leads to reprogramming of cellular activities, including changes in pathogen responses, such as ROS production and modifications of the cell wall. Our data shows the function of the MAPK phosphatase AP2C in regulation of MAPK activities, ROS production and callose deposition during pathogen associated molecular pattern (PAMP)- or pathogen-induced stress. Taken together this data shows that AP2C controls plant immune responses, emphasizing the important roles of PP2C-type MAPK phosphatases in plant innate immunity