Mitogen-activated protein kinases （MAPKs） are involved in the regulation of plant growth, development and responses to a wide variety of stimuli. In a conditional gain-of-function transgenic system, the activation of AtMEKS, a MAPK kinase, can in turn activate endogenous AtMAPK3 and AtMAPK6, and can lead to a striking increase in ethylene production and induce hypersensitive response （HR）-like cell death in Arabidopsis. However, the role of the increased ethylene production in regulating this HR-like cell death remains unknown. Using Arabidopsis transgenic plants that express AtMEK5DD, an active mutant of AtMEK5 that is under the control of a steroid-inducible promoter, we tested the contribution of ethylene to cell death. We found that ethylene biosynthesis occurs before cell death. Cell death was delayed by inhibiting AtMEKS-induced ethylene production using inhibitors ofACC-synthases, ACC- oxidases or ethylene receptors. In the mutants AtMEK5^DD/etrl-1 and AtMEK5^DD/ein2-1, both of which showed insensitivity to ethylene, the expression ofAtMEK5DD protein, activity of AtMAPK3 and AtMAPK6, and ethylene produc- tion were the same as those seen in AtMEK5^DD transgenic plants, but cell death was also delayed. These data suggest that ethylene signaling perception is required to accelerate cell death that is induced by AtMEK5 activation.
Hongxia Liu Ying Wang Juan Xu Tongbing Su Guoqin Liu Dongtao Ren
