Analysis of the MKK1 and MKK2 stress signaling pathways

Environmental stresses negatively affect growth and yield of all plants. Therefore, the understanding of the molecular mechanisms of adaptation to environmental stresses has been a major topic of plant research during the past ten years. Recent work concentrated mainly on the identification of stress-induced genes, either applying genetic screens or expression profiling using DNA microarrays. In several cases, overexpression of the identified genes resulted in improved stress tolerance in plants. The molecular mechanisms leading to the induction or activation of these genes are still incompletely understood. We have recently identified a stress MAP kinase pathway in Arabidopsis, involving the MAP kinase kinase MKK2 and the two downstream MAP kinases MPK4 and MPK6. Overexpression of MKK2 in plants resulted in increased chilling and salt tolerance. Using transcript, phosphoprotein as well as metabolite profiling techniques, this proposal aims at the mechanism and the identification of the molecular targets of this stress pathway.

MPK4 encodes a highly conserved protein kinase that plays a cardinal role in the regulation of the immune response. To understand how MPK4 performs this role, we analysed the physiology of mpk4 mutants and identified the target genes and substrate proteins of this kinase. In the course of the project, new methods were successfully developed to isolate and identify the components of different protein complexes formed by MPK4. Our results reveal that MPK4 is a central regulator integrating innate immune responses with cell division and the cytoskeleton of plants.