Mitogen-activated protein kinase phosphatase is required for genotoxic stress relief in Arabidopsis

Genotoxic stress activates complex cellular responses allowing for the repa ir of DNA damage and proper cell recovery. Although plants are exposed cons tantly to increasing solar UV irradiation, the signaling cascades activated by genotoxic environments are largely unknown. We have identified an Arabi dopsis mutant (mkp1) hypersensitive to genotoxic stress treatments (UV-C an d methyl methanesulphonate) due to disruption of a gene that encodes an Ara bidopsis homolog of mitogen-activated protein kinase phosphatase (AtMKP1). Growth of the mkp1 mutant under standard conditions is indistinguishable fr om wild type, indicating a stress-specific function of AtMKP1. MAP kinase p hosphatases (MKPs), the potent inactivators of MAP kinases, are considered important regulators of MAP kinase signaling. Although biochemical data fro m mammalian cell cultures suggests an involvement of MKPs in cellular stres s responses, there is no in vivo genetic support for this view in any multi cellular organism. The genetic and biochemical data presented here imply a central role for a MAP kinase cascade in genotoxic stress signaling in plan ts and indicate AtMKP1 to be a crucial regulator of the MAP kinase activity in vivo, determining the outcome of the cellular reaction and the level of genotoxic resistance.