MAPK signalling and plant cell survival in response to oxidative environmental stress

Summary

Plant cells must constantly monitor and manage the levels of reactive oxygen species (ROS) accumulating within their cytosol and organelles. Extensive enzyme and metabolite-based antioxidant systems help regulate redox homeostasis, but how these systems are regulated in response to ROS challenge has remained obscure. One of the earliest responses to ROS perturbations in plants cells is the activation of specific mitogen-activated protein (MAP) kinases. Since MAPkinase cascades are involved in many aspects of eukaryotic signal transduction, these ROS-responsive kinases seem likely to form a key part of the antioxidant regulation network. Using ozone; a potent ROS generator and a phytotoxic air pollutant, we have demonstrated rapid and transient activation of MAPKs in various plant species. Genetic manipulation of the ROS-responsive MAPKs, SIPK/AtMPK6 in tobacco and Arabidopsis respectively, render the plants hypersensitive to ozone. Examination of MAPK activation profiles following ROS stress in SIPK/MPK6 transgenic plants reveals an interesting interplay between SIPK/MPK6 and another MAPK, WIPK/MPK3. Proteomic analysis of specifically suppressed transgenic lines has provided novel insights into the specific metabolic networks controlled by the ROS-responsive MAPK cascades during the cell’s response to oxidative challenges. We have also been able to extend the same findings to poplar through heterologous expression of SIPK, which provides evidence for the potential of exploiting MAPK pathways for crop improvement.