Regulation of MAPK Phosphatase 1 (AtMKP1) by Calmodulin in Arabidopsis

Abstract

The mitogen-activated protein kinases (MAPKs) are key signal transduction molecules, which respond to various external stimuli. The MAPK phosphatases (MKPs) are known to be negative regulators of MAPKs in eukaryotes. We screened an Arabidopsis cDNA library using horseradish peroxidase-conjugated calmodulin (CaM), and isolated AtMKP1 as a CaM-binding protein. (MEKK). The MAPKs are activated by MEK via the phosphorylation of threonine and tyrosine residues within a conserved TXY motif (14, 15). MAPKs are inactivated by protein phosphatases such as tyrosine-specific phosphatase, serine/threonine-specific phosphatase, and dual specificity phosphatase, through specific dephosphorylation of threonine and tyrosine residues within the TXY consensus sequence (16, 17). MAPK phosphatases (MKPs) belong to the dual specificity phosphatase (DsPTP) family and dephosphorylate both phosphotyrosine and phosphoserine/phosphothreonine residues (18). Only five members of the MKPs, including the previously described AtDsPTP1, IBR5, PHS1, and AtMKP1, are predicted to exist in the Arabidopsis genome, and these five MKPs are responsible for the modulation of 20 potential MAPKs (18,19). The MKP/MAPK ratio in Arabidopsis is disproportionately low compared with other eukaryotes, implying that plants may possess integrated and complicated mechanisms for the regulation of MAPK signaling through MKPs.Plant MKPs play important roles in various biotic and abiotic stress responses. AtMKP1 was reported to be involved in genotoxic stress signaling (20) and AtMKP2 in the regulation of the cellular response to oxidative stress in Arabidopsis (21).

Redox Regulation in Plant Immune Function

“…Mutational analyses suggested that Cys 235 was the essential residue for redox sensing in PTP1: replacement by Ser abolished phosphatase activity (119). Illustrating the complexity of ROS/ RNS cellular networks and feedback loops, both MKP1 and PTP1 were shown to bind CaM and activity was increased by CaM in a Ca 2 + -dependent manner (64).…”

Calmodulin-binding protein CBP60g is a positive regulator of both disease resistance and drought tolerance in Arabidopsis

“…In Arabidopsis, MAP kinase phosphatase1 (MKP1) is a calmodulin-binding protein regulated by CaM through two Ca 2? -dependent CBDs (Lee et al 2008). AtMKP1 has a role in genotoxic stress resistance and negatively regulates salt stress tolerance (Ulm et al 2002).…”

Recent Advances in Calcium/Calmodulin-Mediated Signaling with an Emphasis on Plant-Microbe Interactions

“…Moreover, Ca 2+ /CaM binds to plant catalase and enhances its activity (Yang and Poovaiah, 2002b). Recently, Ca 2+ /CaM was also reported to regulate H 2 O 2 -mediated defense responses by regulating the MAPK cascade through the action of MAPKs and MAPK phosphatases (Lee et al, 2008;Bartels et al, 2009;Takahashi et al, 2011).…”