Control of MAPK signaling by PP2C-type MAPK phosphatases in Arabidopsis.

Irute Meskiene, University of Vienna, Austria and Institute of Biotechnology, Vilnius, Lithuania

The ability to survive unfavorable environment is an essential property of every organism. Since plants, in contrast to animals, are sessile organisms and thus can´t escape their surroundings, they rely heavily on innate mechanisms of sensitive recognition and effective response to signals generated by external factors. Remarkably, recognition of diverse microbe associated molecular patterns (MAMPS) by multiple plant cell receptors converge on the same MAPKs, represented in Arabidopsis by MPK3 and MPK6, indicating that plant cells ensure regulation of specificity for appropriate signaling responses. Additionally, MPK3 and MPK6 control initiation of stem cells and their differentiation in plants. We are studying negative regulators of MAPKs in Arabidopsis the protein phosphatases of PP2C-type, called AP2Cs, which specifically interact with and inactivate MAPKs MPK3 and MPK6. AP2Cs dephosphorylate pT in pTEpY activation loop of MAPKs and this is sufficient to render MAPK inactive. Investigation of AP2C knock out mutants and overexpressing plant lines provided genetic evidences and enabled identification of specific roles of these phosphatases in plant innate immunity and development. We found that subcellular localization of these MAPK phosphatases strongly influences MAPK signaling outcome. Our studies involving analyses downstream of MAPK activation, including plant defence responses, qRT-PCR of global transcription factors and plant hormone measurements suggest that negative regulators of MAPKs AP2Cs contribute to specificity of cell signaling by MAPKs in plant cells. Taken together, our results provide more understanding on regulation of MAPK signaling pathways in plants and highlight the cell-autonomous mechanism of plasticity plants display in order to adapt to environmental stress.