MAPK activity and MAP kinase phosphatase 2 (AtMKP2) protein stability under altered glutathione homeostasis in Arabidopsis thaliana

Mitogen-activated protein kinases (MAPKs) are important signaling players involved in various responses to diverse environmental stresses. MAP kinase phosphatases (MKPs) are crucial negative regulators of MAPKs and control the intensity and duration of MAPK activation. It has been shown that transgenic tobacco plants with increased glutathione content display an oxidative shift and have constitutively active immunity-related MAPKs. The mechanism by which glutathione can activate or keep these MAPKs in activated state is unclear. In this study, it is shown that the Arabidopsis stress-related MAPKs, AtMPK3 and AtMPK6 are hypersensitive to a pathogen-associated molecular pattern flg22 in the cat2-1 line, under the conditions causing an altered glutathione homeostasis and elevated oxidative stress responses in this background. As AtMKP2 is the only dual specificity phosphatase deactivating AtMPK3 and AtMPK6 in response to oxidative stress, the stability of the wild-type AtMKP2 protein and the mutant version of the protein with the substitution of the cys109 in the active site with serine has been studied in wild type (Col-0) and cat2-1 background. The results indicate that AtMKP2 is a stable protein in both genetic backgrounds, whereas the active site cys109 stabilizes the protein under severe oxidative stress conditions and can be glutathionylated in vitro.