Studies on the molecular mechanism of osmotic stress signaling in plants

The intensive use of fertilizers and artificial irrigation has contributed to high soil salinity in many areas of the world. By now, high salt content of the soil has become a major limiting factor in agricultrual performance. As adaptation to salinity relies on expression of specific gene products, initial efforts concentrated on the identification of salt stress-induced genes. In contrast to the rapidly growing list of such genes, we still have little understanding of how cells sense and transmit salt stress. In yeast and mammalian cells, salt stress is signaled through highly conserved MAP (mitogenactivated protein) kinase cascades. We have recently identified the MMK1 MAPK pathway that is activated by salt stress in intact plants and cultured cells. In this work, a genetic investigation of the biological function of the MMK1 pathway with respect to salt stress adaptation will be performed. The MMK1 pathway will be analyzed by identifying upstream and downstream components. The interaction and function of these components within the pathway will be investigated at the molecular level by both genetic and biochemical means. Because the activation of MAPKs is correlated with a nuclear translcoation, part of the project will focus on the molecular mechanism underlying the cellular localisation by means of expressing and analysing different mutated MMK1 constructs. The capability of the mutant MMK1s to undergo intracellular translocation will be monitored by indirect immunefluorescence microscopy and by real time video microscopy with green fluorescent protein (GFP) fusion constructs.